Backyard Poultry Primer


What is a galliform?

Order Galliformes consists of heavy-bodied, ground-feeding land fowl, like the chicken (Gallus gallus), turkey (Meleagris gallopavo), peafowl (Pavo cristatus), as well as quail, guineafowl, and pheasant.38 The most common gallinaceous birds encountered in clinical practice are chickens and turkeys.10,36


What is a backyard flock?

Backyard poultry consist of meat and game birds. These hobby flocks may include ‘rehomed’ commercial hens as well as ornamental and show birds (Fig 1).39 Backyard poultry are increasingly popular.11,18,36,39,48,50 Although most small, backyard flocks are found in rural areas, their numbers have increased greatly in urban and suburban areas.7,18,36,50 Most flock owners raise poultry for meat or egg production for their own personal consumption.10,18,21,36 Backyard fowl are rarely vaccinated unless the collection is very large, it is a breeding flock, or there is a history of chronic disease in the flock.12 Owners often follow husbandry practices similar to that for free-range poultry, in which birds have access to an outdoor environment and forage material during the day.29

Backyard flock

Figure 1. Most backyard or hobby flocks are owned for meat or egg production. Image by Tabii. Click image to enlarge.

Due to their small size, noncommercial backyard flocks are not recorded in national databases. For instance, the Animal and Plant Health Agency does not report flocks less than 50 birds.39 California defines backyard poultry as flocks less than 1,000 birds, however all other states defined backyard poultry as any flock that was not classified as a commercial producer.14 Surveys of backyard flocks have found that most flocks consist of less than 10 to 50 birds.11,25,36


Clinical approach

Taking the history

Backyard hens are seen by avian veterinarians more frequently now than ever before.26 The history for the backyard fowl should include all the standard questions asked for the avian patient as well as vaccination history (Fig 2). Also determine…

  • Is the bird considered a pet or strictly a source of food? This information will impact treatment decisions. Many backyard poultry owners view poultry more as pets than production animals.8,21,27,36
  • Is the flock open or closed? Pathogens in poultry can be transmitted between backyard flocks through several routes, including the purchase and sale of birds, movement of birds through markets, presentation at shows, as well as exposure to wild birds.39
  • Do caretakers have outside contact with other poultry that could serve as a source of disease?
  • What is the type of food and water source? Birds on commercially prepared feeds are less likely to succumb to nutrition-related diseases.
  • What is the type of housing?

Download the client education handout “Care of the Backyard Chicken” for additional information on basic husbandry practice.

Consider if the bird is pet or food

Figure 2. Determine during the history if the bird presented is considered a pet or strictly a source of food. Image of ‘Buttercup’ the pet chicken by B. Dubya. Click image to enlarge.

Most backyard poultry owners do not employ even simple biosecurity measures, such as use of dedicated shoes, and few benefit from vaccination of birds. This is unfortunate, since birds purchased directly from National Poultry Improvement Plan hatcheries showed a reduced antibody prevalence to important poultry diseases, such as Newcastle disease, Mycoplasma gallisepticum, and M. synoviae.19

Public health concerns


Backyard poultry owners may be at higher risk for exposure to zoonotic diseases, such as Salmonella spp. and highly pathogenic avian influenza (HPAI), than with commercial poultry flocks due to their inconsistent preventive medicine practices and access to veterinary care.3,19,36 Backyard flocks may also serve as reservoirs of disease for commercial flocks. Some outbreaks of virulent Newcastle disease and Marek’s disease have originated in backyard flocks.36,41

Download the client education handout “Poultry and Public Health” for additional information.

If you suspect disease in a hobby flock, know that there are programs funded through state departments of agriculture or the US Department of Agriculture (USDA) that offer free or reduced cost autopsies, free infectious disease testing for diseases like avian influenza virus and Newcastle disease, and even field services.14



Antimicrobial therapy of poultry is also a matter of public health concern. When antimicrobials important for therapeutic use in humans are used in food animals, this can have an impact on the bacterial populations of humans both directly and indirectly through the formation of antibiotic-resistant organisms.26 Therefore, whether the bird is a pet or a production animals, any food animal species that has the potential to enter the human food chain should not be administered a prohibited drug.27

As a measure to protect public health, regulatory groups around the world create lists of drugs and drug classes that are either completely prohibited or prohibited from extra-label drug use (ELDU) in food‐producing animals (Table 1).27 In the US, the Food & Drug Administration (FDA) Center for Veterinary Medicine has established guidance on the “The judicious use of medically important antimicrobial (MIA) drugs in food‐producing animals”.27,49 There are three prohibitions proclaimed by the FDA that impact chickens and turkeys:  antiviral medications, use of any fluoroquinolones, as well as ELDU of cephalosporins.27,39 If a prohibited drug is mistakenly used in poultry, then the affected animal and its by‐products should never be allowed to enter the human food chain.27 Ideally, the animal should also be isolated from other birds that are used as food producers for humans.27

Clinical Tip:  Check the prohibited drug list in your nation on a regular basis for updates and follow label instructions for drug therapy. If extralabel drug use is employed, consult a regulatory resource, such as in the US, to identify an acceptable withdrawal time.26,27

Table 1. Online resource providing information on veterinary drugs in poultry 27
Animal Drugs @ FDAFDA database of approved animal drugs and tolerances
Animal Health and Production CompendiumCentre for Agriculture and Bioscience International (CABI)’s list of international animal drug databases
Canadian Global Food Animal Residue Avoidance Databank (gFARAD)Withdrawal recommendations following extra‐label drug use
Food Animal Residue Avoidance Databank (FARAD)Prohibited and restricted drugs in food animals
Food Animal Residue Avoidance Databank (FARAD) Approved VFD Drug CombinationsVeterinary feed directive (VFD) drug combinations approved by the US Food and Drug Administration
Food Animal Residue Avoidance Databank (FARAD) Species PagesCovers species related information and topics related to drug use in food animals
Minor Use Animal Drug ProgramSearchable database for drugs approved in minor food animal species. Minor species being all gamebirds except for chicken and turkeys
NOAH CompendiumUK National Office of Animal Health searchable drug compendium of approved drugs
PubCRISAustralian Pesticides and Veterinary Medicines Authority searchable database of registered pesticides and veterinary drugs
VetgramFood Animal Residue Avoidance Databank (FARAD) drug database for food animal drugs and tolerances


Backyard poultry farming often arises from the belief that home-raised chicken eggs are healthier, safer, and more sustainable alternatives to commercial store-bought eggs.36,42 Unfortunately, backyard layer chickens may be exposed to a variety of metals in the environment, including lead.42 Lead has been detected in backyard chickens in both rural and urban areas, and yet these chickens typically lack obvious clinical signs making early detection and diagnosis difficult.42 Raise awareness in chicken owners and in higher risk environments, such as older urban homes. Testing environmental samples prior to bird placement is recommended and post-placement monitoring of birds and eggs should be considered.42

Conditions commonly seen in backyard fowl

Conditions commonly encountered in backyard chickens and turkeys often include endoparasites, like Eimeria spp., and infectious diseases, including pasteurellosis or fowl cholera, mycoplasmosis, staphylococcosis, Marek’s disease, and colibacillosis or E. coli septicemia. Other common presenting problems include reproductive disease and trauma, which can typically be categorized as attack wounds or long bone fractures (Fig 3).11,14,29,36
39 Keep in mind that concurrent disease is common in backyard flocks. In one survey, 69% of cases had more than one possible cause of death listed.14

Chicken meets cat

Figure 3. Traumatic injury like bite wounds are a common presenting problem for backyard poultry. Image by Steve P. Click image to enlarge.

Below you will find a collection of differential diagnosis lists for common clinical problems observed in the gallinaceous bird. These abbreviated lists should in no way replace professional judgment when evaluating your patient. This “cheat sheet” is merely designed as an aid or reminder system and should never be used for diagnostic decision-making.


Diseases featured in the primer

Avian influenza
Fowl cholera
Gastrointestinal impaction
Infectious laryngotracheitis
Internal lay
Lice and mites
Lymphoid leukosis
Marek’s disease virus
Mycoplasma gallisepticum
Mycoplasma synoviae
Newcastle disease virus


The fluffed and ruffled bird

Fowl are stoic patients that commonly mask signs of illness in the early stages of disease.38 Ill birds frequently present with non-specific signs of illness including fluffed and ruffled plumage, depression, anorexia, and a hunched appearance. Important rule-outs for the fluffed and ruffled galliform include:26,27,29,39


Colibacillosis refers to any localized or systemic Escherichia coli infection caused by avian pathogenic E. coli or APEC.1,27,34 Escherichia coli infection can occur in birds of all ages, but is most common in chicks and poults less than or equal to 1 week of age (Fig 4).1 Disease can develop secondary to fecal contamination of eggs. Colibacillosis can also be transmitted by inhalation or ingestion; this most frequently occurs when birds are housed indoors during cold weather periods.27,34

Young chicks

Figure 4. Colibacillosis is commonly seen in chicks and poults 1 week of age or younger. Image by Ian S.H. Click image to enlarge.

Escherichia coli causes various disease syndromes in poultry. Infection in neonatal poultry is characterized by acute septicemia.45 If infection involves the yolk sac (omphalitis), then the umbilicus will also appear inflamed.27,45 Affected birds are lethargic and edematous. The subacute form of disease can manifest as pericarditis, perihepatitis, and air sacculitis.45 Escherichia coli commonly affects the respiratory tract of both chickens and turkeys, often causing air sacculitis in the subacute form of disease.27,45 Pericarditis and perihepatitis may also be seen.45 Surviving hens can develop salpingitis and retained eggs. The coelom of affected birds can be greatly distended due to an accumulation of egg debris within the oviduct.

Fowl cholera

The Gram-negative rod Pasteurella multocida causes fowl cholera or avian cholera.6 Outbreaks of avian cholera are most often reported in chickens, turkeys, domestic ducks, and geese, however other types of gallinaceous birds, companion birds, and wild birds can also be infected.6 Among chickens, death typically occurs in older, laying flocks.3 Younger birds (less than 16 weeks of age) are relatively resistant.27 Fowl cholera appears to be less frequent in the United Kingdom than in North America, where annual outbreaks cause significant mortalities.38 Pasteurellosis is sporadically seen in backyard flocks, especially those with exposure to other poultry through bird shows. Pasteurella multocida isolated from birds with fowl cholera will usually kill rabbits and mice, but other mammals are resistant.27

Fowl cholera is classically an acute disease that causes septicemia with high morbidity and mortality rates.6,27 Clinical signs can include:

      • Fluffed and ruffled feathers
      • Depression
      • Fever
      • Anorexia
      • Mucoid discharge from the mouth
      • Diarrhea
      • Tachypnea
      • Cyanosis

Cyanosis often develops immediately before death, and is most evident on unfeathered areas of the head, like the comb and wattle.6 The course of disease lasts only a few days, therefore death is sometimes the first finding recognized by owners, particularly in turkeys.6,38 Survivors of the acute form of fowl cholera can later succumb to debilitation secondary to emaciation and dehydration. Birds can also become chronically infected and recover.6

The respiratory tract is an important site of chronic P. multocida infection causing infraorbital sinusitis, tracheal rales, and dyspnea. Clinical signs can also be related to localized infections. For instance, local infection involving the middle ear and/or cranial bones can cause torticollis. Clinical signs of focal infections can include: 27

      • Conjunctivitis
      • Exudative pharyngeal lesions
      • Joint and/or foot pad swelling
      • Swollen sternal bursa
      • Swollen wattle (chickens)
      • Torticollis

A tentative diagnosis of acute fowl cholera can be made by demonstrating bipolar organisms in liver imprints using Wright’s stain. Immunofluorescent microscopy can also be used to identify P. multocida in tissue or exudate. Definitive diagnosis relies on isolation of the organism from tissues or blood. Pasteurella spp. can be readily isolated from birds with acute fowl cholera and usually from lesions of chronic cases. The organism is less likely to be grown from debilitated survivors of an acute outbreak. Bone marrow, heart blood, liver, meninges, and focal lesions are preferred samples for culture. Antemortem samples can include choanal swabs, nasal flush samples, or sinus aspirates.9

Necropsy findings in acute fowl cholera are associated with vascular disturbances, such as petechia, ecchymoses, and generalized hyperemia. Large numbers of bacteria are often seen microscopically within blood vessels.9

Antimicrobials are most likely to be successful in the treatment of fowl cholera when they are initiated promptly and based on sensitivity results. Like many Gram-negative organism, strains of Pasteurella can vary in susceptibility to chemotherapeutic agents. Sulfonamides and feeds containing tetracyclines are popular empirical choices.9,27

Pasteurella multocida can survive in the environment for up to 2 weeks.3 When separated from organic material, P. multocida is destroyed easily by common disinfectants, sunlight, drying, and at temperatures exceeding 56°C. 6

Gastrointestinal impaction

Unlike conventional commercial poultry, backyard flocks are typically managed in free-range or pastured settings, which exposes birds to a variety of poorly digestible items.29 Birds that are placed in new environments and other stressful situations are more prone to eating non-feed substances.29 Birds may also peck at fibrous materials out of curiosity.29,37,38 Poultry have been known to ingest long grasses, newspaper, wood shavings, feathers, and compacted feed leading to impaction of the crop, esophagus, proventriculus, or ventriculus.29,37,38 Crop impaction is most frequently seen in the spring, when chickens ingest long stems of grass.38

Anorexia and lethargy are common clinical signs.38 Physical exam findings in some birds include emaciation and esophageal or crop distension.29,38 Ventricular impaction can cause high mortality during the first 3 weeks of life in turkey flocks.38 A case series in 40 chickens, one turkey and one goose with gastrointestinal impaction described sudden death in four individuals.29 Clinical signs were observed for up to 60 days, lasting an average of 7 days in other birds.29

Although surgical intervention may be indicated, conservative management that focuses on rehydration, gentle massage, and/or flushing of the crop or esophageal impaction may resolve the impaction in early cases.29,38 Prevention of impaction in backyard fowl relies on maintenance of short pastures, avoidance of feeds that can expand in the gastrointestinal tract, and provision of adequate grit.25 Owners should also take measures to minimize stress.29

Lymphoid leukosis

Lymphoid leukosis is a retroviral infection that causes tumors in chickens 14 weeks of age and older. The incidence of avian leukosis is typically low (<4%), however, mortality can be high in affected birds. Lymphoid leukosis is transmitted transovarially; hens shed virus into eggs. Chicks are then infected at hatch and shed virus their entire lives. Necropsy findings include profound hepatomegaly, bursal enlargement, and neoplastic nodules. Unlike Marek’s disease virus, neural involvement does not occur in lymphoid leukosis.27

Newcastle disease virus
There are 11 serotypes of avian paramyxovirus designated APMV-I to APMV-11.30 Newcastle disease (ND) is caused by virulent strains of Newcastle disease virus (NDV) or avian paramyxovirus 1 (APMV-1), recently renamed avian avulavirus 1.12,20,30 Newcastle disease affects poultry species and wild birds worldwide.12 Wild bird reservoir species include columbids (pigeons and doves) and double-crested cormorants (Phalacrocorax auritus).12 Newcastle disease can cause significant economic losses in the poultry industry and is considered one of the most important pathogens of poultry.12,20 Newcastle disease is enzootic in poultry throughout much of Africa, Asia, and parts of Latin America.12 In more developed regions, sporadic epizootics occur on a fairly regular basis. Four worldwide panzootics have been recognized since ND was first discovered in 1926.12 For this reason, ND is monitored by the Food and Agriculture Organization of the United Nations as well as the World Organisation for Animal Health (OIE).12,20 Virulent ND is listed as a Tier 1 USDA Select Agent as a pathogen of national concern and a significant threat to animal agriculture in the US.12

Newcastle disease virus has been categorized into three main pathotypes based on the clinical signs seen in infected chickens (Table 2).12,30 Lentogenic isolates are of low virulence. Mesogenic viruses are of intermediate virulence, while velogenic viruses can cause high mortality.12,30 Velogenic forms of NDV are further classified as neurotropic or viscerotropic.12,30 Variations in host and virus strains means that clinical disease can range from asymptomatic to severely pathogenic with major economic losses. Drops in egg production may be observed in well-vaccinated layers and mild upper respiratory disease, such as conjunctivitis or tracheitis may also be seen. High morbidity and up to 100% mortality can be seen in naïve or poorly vaccinated chickens.20,38
Table 2. Avian paramyxovirus-1 can be broadly grouped into pathotypes
FormRespiratory signsNeurologic signsEgg productionGastrointestinal signsComments
Viscerotropic velogenic Newcastle disease (VVND)Signs often begin with tachypnea, listlessness, weakness Prior to death, muscle tremors, torticollis, paralysis of legs and wings, opisthotonos can be apparentGreen diarrhea is frequently seen in birds that do not die early in infectionCan cause edema around eyes and head; mortality frequently reaches 100% in flocks of fully susceptible chickens
Neurotropic velogenicSudden onset of severe respiratory diseaseNeurologic signs follow respiratory signs after 1-2 daysEgg production falls dramaticallyDiarrhea is usually absentMorbidity can reach 100%, mortality is generally considerably lower (up to 50% in adults and 90% in juvenile birds has been reported)
MesogenicUsually causes respiratory disease in field infectionsNeurologic signs can occur but are not commonMarked drop in egg production can last for several weeksMortality is usually low except in very young, susceptible birds
LentogenicSerious respiratory disease in young, susceptible birdsDoes not usually cause disease in adults, young birds often die
Newcastle disease is primarily transmitted by inhalation or ingestion of virus shed in feces and respiratory secretions.12 Some viral isolates have been found to be transmitted through the egg to the hatching chick.12 Newcastle disease is highly contagious with the potential to rapidly spread to naïve birds. Backyard game fowl have been implicated in multiple ND outbreaks in the US and Europe, and backyard flocks are of great concern in ND because of the lack of vaccination and biosecurity in these populations paired with their exposure of backyard poultry to wild birds and environmental factors means that these populations may serve as amplification hosts which increases the probability that virulent ND will spill over into commercial poultry flocks due to large amounts of circulating virus.12 The highest risk factor for these commercial flocks was found to be farm employees exposed to infected backyard flocks.

In 2018, virulent Newcastle disease virus was detected in sick, backyard, exhibition chickens in southern California. Since then, the virus has affected 401 backyard and four commercial flocks, and one live bird market in California, and one backyard flock in Utah.20 This was the first report of virulent ND in the US in over 15 years.20 The last outbreak of velogenic NDV in the United States occurred in 2002–2003 in California, Nevada, Arizona, and Texas in domestic poultry. Disease was confined to backyard flocks in the latter three states, but did spillover into a commercial operation in California.12

Avian paramyxovirus is diagnosed by direct detection of viral antigens and/or viral isolation from cloacal or pharyngeal swabs.

Both live and inactivated vaccines are widely used. Newcastle disease vaccines have demonstrated protective efficacy to reduce the likelihood of outbreaks, however, these vaccines are unable to block the replication and shedding of most of the currently circulating phylogenetically divergent virulent NDV isolates.38 Vaccination against ND is not currently allowed in the UK.38 Control of ND must also include strict biosecurity.

Newcastle disease also has some zoonotic potential.12 In humans, the virus can cause conjunctivitis, blepharitis, epiphora, subconjunctival hemorrhage, and/or flu-like symptoms, such as fever, headache, and lethargy.12 Infections are usually transient.12 Exposure to large amounts of virus is necessary, therefore human infections are most commonly seen in poultry farm or slaughterhouse workers.12 There are two reports of death linked to ND: lethal pneumonia in a middle-aged man with lymphoma following a peripheral blood stem cell transplant and fatal encephalitis in a child.24,52

Reproductive problems

Reproductive problems are a common finding in backyard poultry.27 Early clinical signs can be non-specific, and owners may not observe or recognize problems in the flock until egg production is influenced.33 Conditions frequently seen include salpingitis or infection of the oviduct, oviduct impaction, internal laying, and egg binding.27

Whenever reproductive disease is confirmed or suspected, the history should include:

        • Has there been a drop in egg production?
        • Has there been a change in the external or internal quality of the eggs?

Egg laying decreases as age increases. A hen lays the most eggs during her first year of sexual maturity. Fewer eggs are laid in the second year, and significant decreases are observed during the third and fourth years. Most hens do not produce eggs after 5 years of egg laying.22

Internal lay (the presence of soft-shelled or fully formed eggs free in the coelom) or yolk coelomitis (peritonitis) usually occur secondary to reverse peristalsis.14,26 This retrograde movement is often believed to occur because of oviductal impaction, abnormal conformation of the oviduct, or oviductal bacterial infection. Bacterial infections often involve E. coli that has migrated up the reproductive tract from the vent.14,26 It is not uncommon for chickens to have some degree of coelomitis, and mild cases are commonly encountered at necropsy in production hens  Generally, chickens tolerate mild coelomitis better than parrots, however clinical signs can include lethargy, partial anorexia, weight loss, and even lameness as the bird struggles to walk with its severely distended coelom.26 Diagnosis of internal lay relies on recognition of consistent clinical signs and radiography. Depending on the stage of egg development, coelomocentesis and aspiration may reveal yolk or an opaque yellow fluid. Medical management includes fluid therapy, antibiotics, nonsteroidal anti-inflammatory drugs, and butorphanol for pain.26 Surgery is recommended for severe cases, particularly when eggs are free in the coelomic cavity or when oviductal impaction is involved.26

Although the right oviduct should regress in the embryo, partial development leading to a cystic right oviduct appears to be more common in backyard poultry when compared to commercial chickens.26 Clinical signs include non-specific signs of illness, a reduction or complete halt in egg laying, and most notably a large, fluctuant coelom. A tentative diagnosis can be achieved through similar means as with internal lay, however ultrasound will also confirm the presence of coelomic fluid and may reveal discrete pockets of fluid or cysts, that can measure up to 10 x 20 cm in size.26

Some birds may be “false layers”. They show the characteristics of egg production, but lay no actual eggs. Reductions in egg laying are a common presenting complaint (Table 3). “False layers” or abnormal egg production can result from prior infection with infectious bronchitis virus (IBV) in chickens.27 Salpingitis can also occur from prior respiratory disease such as E. coli air sacculitis.27

Table 3. Important causes of drops in egg production in gallinaceous birds 14,26,27
Husbandry-relatedChange in management
Temperature change
Eggs eaten by predatorsEgg production appears to drop but is in fact normal
Eggs destroyed by penmatesEgg production appears to drop but is in fact normal
Viral diseaseNewcastle disease virusChickens, turkeys
Infectious bronchitis virus (coronavirus)Chickens, all agesNot common in backyard poultry
Avian influenza
Infectious laryngotracheitis Chickens
Fowl pox
Avian encephalomyelitis
Lymphoid leukosisChickens
Marek’s disease virusChickens
Coronavirual enteritisTurkeys
Eastern equine encephalitis Japanese quail, pheasants
Bacterial diseaseEscherichia coli
Fowl cholera Salpingitis, retained eggs
Mycoplasmosis Salpingitis
Infectious coryzaChicken
Parasitic diseaseEndoparasitesIncluding coccidiosis
Nutritional diseaseCage layer paralysisHigh egg producing breeds like Leghorn chickens may be more susceptible to cage-layer fatigue30
Fatty liver hemorrhagic syndrome
Low-salt diet

Neoplasia is also an important cause of morbidity and mortality in small flock birds.11 In one survey, neoplasia was the most common non-infectious cause of mortality, accounting for 11% of deaths.11 Adenocarcinoma of the ovary or oviduct were particularly common.11,14

Important rule-outs for external egg changes like misshapen eggs, chalky egg shells, thinly shelled eggs, or shell-less eggs include conditions that affect the oviduct in general and the shell gland or uterus in particular such as:

An important cause for internal egg changes like watery egg whites is prior infection with infectious bronchitis virus.27,28

The roundworm of chickens and turkeys, Ascaridia galli, is a common problem in backyard poultry. Roundworms can occasionally be found in eggs when birds are heavily parasitized. Worms exit the rectum, and then enter the oviduct via the cloaca where they can become incorporated into the egg.27

Respiratory signs

Important causes of respiratory disease in backyard fowl include fowl cholera, mycoplasmosis, infectious laryngotracheitis (ILT) (Fig 5) (Table 4). Mixed respiratory infection is often the most common cause of death or illness.11 Coinfections typically involves bacteria, like Mycoplasma gallisepticum, M. synoviae, E. coli, Ornithobacterium rhinotracheale, or Avibacterium spp., and viruses, such as ILT or avian poxvirus.2,11,25 Common combinations of respiratory pathogens associated with primary lesions in small chicken flocks were M. gallisepticum, M. synoviae, and IBV and M.  gallisepticum, M. synoviae, IBV, and ILT.11

Sinusitis in the chicken

Figure 5. Sinusitis is a common presentation in chickens. Important causes of sinusitis in galliforms include mycoplasmosis, cryptosporidioisis, E. coli, and pasteurellosis. Image provided by Dr. M. Scott Echols. Click image to enlarge.

Table 4. Important causes of respiratory disease in gallinaceous birds 27,38
DiseaseSignalmentClassic clinical presentation
Bordetella avium
(Turkey coryza)
Sporadically seen in backyard turkey
Sneezing (snicking)
Nasal discharge
Tracheal rales
Uncommon in closed flocks
Mycoplasma gallisepticumCommon in backyard chickensNasal discharge
Cough-like sounds
Tracheal rales
Sinusitis is especially common in turkeys, peafowl
Pasteurella multocida (fowl cholera)Adult chickens and turkeysDyspnea and high mortality in the acute form of disease in turkeys
Sinusitis is especially common in turkeys, peafowl
Swollen wattles
Avian influenza Mostly frequently reported in free-flying aquatic birds (ducks, geese, shorebirds, gulls, terns, auks). Sporadically isolated from domestic poultry, most frequently chickens, turkeys, and ducks.Sneezing
Cough-like sound
Infectious bronchitis virus (coronavirus)ChickensNasal discharge
Cough-like sound
Tracheal rales
Internal and external egg quality is also affected
Infectious laryngotracheitis (herpesvirus)Chickens (especially show chickens), pheasants; usually > 5 weeksCough-like sounds
A bloody, mucoid expectorant is produced in severe cases, especially noticeable in white feathered birds
High mortality
Newcastle disease virusMost species of domestic, aviary, and free-ranging birds have been found to be susceptible. Lentogenic and mesogenic strains are common in domestic fowl in the United States.Cough-like sounds
(wet form)
All species of birds are susceptible to some strain of pox. Diphtheritic lesions frequently occur in infected pheasants and quail.White nodules or caseous plaques on mucosa of oropharynx, larynx, trachea cause dyspnea, high mortality
CryptosporidiosisTurkey, quailSneezing
Cough-like sounds
Tracheal rales
High mortality in quail
Tracheal worms or gapeworms Genus Syngamus (chickens, turkeys, pheasants, peafowl); Cyathostoma (turkeys)Tracheal rales
Flicking or head shaking

Aspergillosis can also be seen in Order Galliformes, but is rarely a primary pathogen in backyard flocks. Infection may occur in immunocompromised individual chickens or when birds are exposed to an overwhelming quantity of spores.11,36

Mycoplasma gallisepticum

The most common cause of chronic respiratory disease in chickens and infraorbital sinusitis in turkeys in Mycoplasma gallisepticum.11,27,38,53 Most commercial flocks are M. gallisepticum free, however this organism is common in backyard chickens. The onset of disease is often insidious. Mycoplasma spp. can be latent within the flock and often causes disease when there is immunosuppression, stress, and concomitant infection. Clinical signs can include non-specific signs of illness, tracheal rales, cough, nasal discharge, conjunctivitis, a drop in egg production, and death. Foamy eye secretions may also be observed in turkeys. Clinical signs can also be more pronounced with concurrent E. coli or ILT infection.27,38 Disease can be transmitted through eggs obtained from non-commercial poultry sources. Mycoplasmosis tends to be variable in severity and duration, but it is typically more severe and prolonged during the colder months. Disease is also more severe in younger birds. Tylosin is licensed for treatment in the UK, EU, and US. Antibiotic therapy does not eliminate Mycoplasma, but it can resolve clinical signs. It is also important to identify and minimize underlying stressors.38

Infectious laryngotracheitis

Infectious laryngotracheitis (ILT) is a highly contagious upper respiratory tract disease of the chicken caused by a Gallid herpesvirus 1 (GaHV-1).7,25,38 Transmission occurs through the upper respiratory and ocular systems.7 The virus can be isolated from infected birds, dust, litter, fomites, water, and beetles.7

Infectious laryngotracheitis affects chickens, mainly meat breeds, as well as pheasants and peafowl.7,25 Disease is primarily seen in commercial poultry but backyard flocks can serve as an important reservoir due to the existence of latently infected birds.7,25 Backyard poultry come in contact with asymptomatic carrier birds at fairs, swap meets, breed show or after new birds are added to a flock.27

There are two distinct clinical presentations in chickens.7,25 Classic disease is a severe acute form characterized by the formation of a diphtheritic tracheal membrane and severe hemorrhagic tracheitis that can cause tracheal occlusion, expectoration of bloody mucus, and significant respiratory distress.7,25,38 Additional clinical signs include sneezing, conjunctivitis, and decreased egg production.25 Mortality rates can be as high as 70%.7 A milder form of ILT is characterized by poor egg production, poor weight gain, mild to moderate catarrhal tracheitis, sinusitis, and conjunctivitis. Morbidity rates are relatively low with the milder form of ILT and mortality which usually range between 0.1% and 2%.

Control of ILT is multifactorial, with biosecurity, management, and vaccination playing key roles.7 Vaccination can be attempted in an outbreak to reduce morbidity and mortality.38 Early vaccination prevents clinical manifestation, but not latent infection. Modified live vaccines are available in the UK, EU, and US.38

Avian influenza

Avian influenza (AI) viruses have a worldwide distribution. The most frequent reports of AI occur in free-ranging aquatic birds like waterfowl, shorebirds, gulls, and terns which are considered reservoirs of AI viruses.15,16,44 In fact, dabbling ducks, like the mallard (Anas platyrhynchos), have the highest reported isolation rates of AI viruses. Up to 60% of juvenile mallard ducks are infected prior to late summer migration.35

Gallinaceous birds are not natural reservoirs of AI viruses. Avian influenza has been sporadically isolated from domestic fowl, most frequently chickens, turkeys, and domestic ducks.15,16 Susceptibility has also been identified in Japanese quail and pearl guinea fowl.2 Most influenza infections in domestic poultry have been from avian-origin influenza viruses, however H1N1, H1N2, and H3N2 swine influenza viruses have infected turkeys, especially turkey breeders.44

Outbreaks of highly pathogenic avian influenza (HPAI) viruses have caused severe illnesses in poultry and humans.15,16,23,47
51 More than 15,000 outbreaks were documented in domestic birds between 2005 and  2018 and 861 human cases were reported between 2003 and 2019.4,16 Avian influenza is associated with severe economic losses and commercial poultry are more likely to be infected when compared to backyard poultry.16,41 Nevertheless, backyard poultry must be carefully monitored. Basic biosecurity measures are rarely implemented in backyard poultry farming systems which can allow HPAI to circulate.23,47

Avian influenza replicates within the respiratory, intestinal, renal and/or reproductive organs, and virus can be shed from the nares, mouth, conjunctiva, and cloaca of infected birds. Influenza virus is transmitted by direct contact or through indirect exposure to virus-contaminated fomites.44

Morbidity and mortality rates are variable in poultry, and depend on virus pathogenicity and the host.15,16 Clinical findings can include:

      • Oculonasal discharge
      • Infraorbital sinusitis
      • Dyspnea, tachypnea
      • Cyanosis
      • Edema of the head, comb, and wattle
      • Subcutaneous ecchymotic hemorrhages of the legs and feet
      • Blood-tinged oral and nasal discharges
      • Green diarrhea
      • Torticollis, opisthotonos, ataxia

Definitive diagnosis of AI relies on viral isolation or direct detection of AI viral proteins or genes in specimens like tissues, swabs, cell cultures, or embryonating eggs. Virus can be commonly recovered from tracheal, oropharyngeal, or cloacal swabs from live or dead birds.44

Oropharyngeal plaques

Important rule-outs for oropharyngeal plaques in the galliform include:27


      • CandidiasisCandida albicans overgrowth usually occurs secondary to prolonged antibiotic use or in poultry raised under harsh environmental conditions11,14
      • Poxvirus
      • Trichomoniasis
      • Vitamin A deficiency
      • (Aspergillosis)
      • (Fowl cholera)




There are many infectious agents that can cause enteritis in galliforms. Important differential diagnoses include:

Table 5. Stool color or consistency as a clue to underlying cause of disease
Stool color or appearance Differential diagnoses
Bloody diarrhea

  • Acute coliform enteritis

  • Clostridium colinum or ulcerative enteritis (quail, chickens, turkeys, pheasants, grouse, etc.)

  • Hemorrhagic enteritis or type II adenovirus (turkeys)

  • Infectious bursal or Gumboro disease (birnavirus)(chickens)

  • Histomoniasis (turkeys)

  • Coccidiosis (Eimeria spp.)


  • Coronaviral enteritis

  • Protozoal disease

(Bacillary white diarrhea)

  • Pullorum disease (Salmonella pullorum)*

  • Chilled birds


  • Yellow urates

  • Erysipelas

  • Fowl cholera

  • Salmonella gallinarum (fowl typhoid)

  • Chlamydiosis

  • Histomoniasis (sulfur-colored stool in turkeys)

* Once the most important disease in poultry, Pullorum disease is now one of the least significant.

Eimeria spp.

Coccidiosis is common in young chickens and turkeys raised on dirt floors. Clinical signs can include failure to gain weight and diarrhea. Heavy loads can be associated with bloody diarrhea, lethargy, fluffed and ruffled plumage, and death. Different Eimeria species affect different parts of the intestinal tract, with some species like E. tenella affecting only the cecum to cause hemorrhagic typhlitis and cecal core formation. Disease can be complicated by infection with E. coli or Clostridium perfringens (necrotic enteritis).27,32 Management of coccidiosis relies upon improving sanitation and feeding medicated starter feed containing amprolium to 6-8 week old.27 Individual birds can be treated with a sulfa drug, amprolium, or another anticoccidial medication of which there are many to choose from.27



Histomoniasis is caused by the protozoan Histomonas meleagridis. Histomoniasis has a complex life cycle that involves the earthworm and common cecal worm, Heterakis gallinarum.32 Histomoniasis can be a serious disease in backyard turkeys. Disease is usually less severe in chickens and in fact, chickens can be an asymptomatic source of Histomonas sp. and Heterakis sp. Turkeys can contract disease by ingesting the protozoan from fresh droppings. Research suggests that contaminated water can also play a role in parasite transmission.31

Histomonas mainly affects the ceca and liver. An early sign in turkeys is sulfur-colored droppings. Affected birds can also display non-specific signs of illness, however many turkeys die acutely.32 Characteristic lesions found at necropsy include circular depressions surrounded by raised, craterlike lesions in the liver and cores of caseated debris in the cecum. Histomoniasis can also be found in the bursa of Fabricius, kidney, spleen, and other tissues.32 Antemortem diagnosis relies of identification of the organism on fecal exam.27

In commercial flocks, histomoniasis was relatively well controlled until the ban on nitroimidazole antihistomonals in the US and Europe in the 1990s. There is currently no product available for treatment of blackhead disease.27,32 Today the emphasis is on prevention by stressing good sanitation practices and keeping chickens and turkeys separated.27 House birds on substrate that minimizes their exposure to earthworms and deworm turkeys regularly to reduce their cecal worm load.27



Neurologic disease

Neurologic disease is common in fowl.38 Important causes of peripheral neurologic signs gallinaceous birds include Marek’s disease (chickens), botulism, and trauma. Other possible causes include nutritional deficiencies, Newcastle disease, avian influenza, and chlamydiosis.

Marek’s disease

Marek’s disease virus (MDV) is a highly infectious disease of chickens caused by a herpesvirus.11,14 Marek’s disease is very rare in turkeys and has only been documented in the US in two birds.28 The natural route of infection is inhalation of virus particles within contaminated dust and feather dander shed from an infected host.8 Transmission of disease has been confirmed in chicks as young as 1 day of age.8

Marek’s disease is the most commonly reported cause of mortality in backyard poultry.14 While commercial poultry are vaccinated against MDV at 1 day of age, disease occurs frequently in backyard chickens. Unvaccinated birds of any age can develop MDV, although less than 14 weeks is frequently described in the literature.11,14

There are four clinical forms of MDV (Table 6). The visceral form is difficult to distinguish from lymphoid leukosis. Marek’s disease virus is an important cause of neurologic disease in backyard poultry (Table 7). In the neurologic form, MDV is often first noticed as gait disturbances, like ataxia or stilted movements. As MDV progresses, birds can exhibit range paralysis in which one leg is stretched forward and the other leg is stretched back. Unilateral enlargement of the sciatic nerve is identified at necropsy.27

Table 6. Forms of Marek’s disease virus 8,27
FormsClinical disease
CutaneousWhite, distinct nodules involving feather follicles
NeurologicAtaxia, stilted gait, range paralysis
OcularBlue-gray discoloration of iris
VisceralLymphoid tumors of liver, spleen
Tumors can also occur in heart, kidneys, intestines
Table 7. Differential diagnoses for central neurologic signs in gallinaceous birds
Bacterial diseaseArizonosis (turkeys)
Fowl cholera
Viral diseaseAvian encephalomyelitis
Avian influenza
Eastern equine encephalitis (ataxia, paresis, paralysis, and/or torticollis in pheasants or Japanese quail)
Marek's disease virus
Newcastle disease virus
Parasitic diseaseBaylisascaris
Fungal diseaseAspergillosis
Nutritional diseaseThiamine deficiency
Vitamin E deficiency
Other non-infectious diseasesBotulism
Heavy metal toxicity




Differential diagnoses for swollen leg joints and footpads in galliforms include:14,27,38,46

      • Traumatic injury
      • Bite wound injury
      • Fowl cholera (localized Pasteurella multocida infections of leg or wing joints)
      • Mycoplasmosis
      • Staphylococcus aureus:  Staphylococcus arthritis is common in poultry raised on wet litter or rough wire surfaces. Infection can involve not only leg joints and footpads, but also tendon sheaths
      • Viral arthritis (reoviruses)
      • Articular gout
      • Rat-bite infection
      • (Erysipelas)

Mycoplasma synoviae

Infections caused by Mycoplasma synoviae are less common than M. gallisepticum. Acute infection is generally seen in 4-16 week-old chickens and 10-24 week old turkeys, although natural infection has been observed in chicks as young as 6 days of age. Local Mycoplasma synoviae infection most frequently causes upper respiratory infection in chickens. Systemic M. synoviae infection causes acute to chronic tenosynovitis or bursitis and air sacculitis in birds.10,22,53

Early clinical signs of infectious synovitis in chickens typically include lameness, retarded growth, and a pale comb. Lameness is the most prominent finding in turkeys, however joint swelling may not be as prominent as in chickens.10,22,27 Additional clinical signs can include:

      • Non-specific signs of illness like lethargy
      • As disease progresses, feathers become ruffled and the comb shrinks in size. In some cases, the comb will appear blue-red.
      • Warm, fluctuant swellings of one or more joints are usually found. Hock joints and footpads are most commonly involved but in some birds most joints are affected.
      • Enlargement or swelling of the sternal bursa or “breast blisters”
      • Most birds continue to eat and drink if food and water are placed nearby, however severely affected birds lose weight.
      • Mortality is usually less than 1%.

Respiratory signs are rarely observed in turkeys. Other clinical signs in turkeys, are similar to those seen in chickens. Lameness is the most prominent finding, however joint swelling may not be as prominent as in chickens.

A presumptive diagnosis of M. synoviae infection can be based on clinical signs. A definitive diagnosis can be made by isolation and identification of the organism. Mycoplasma synoviae is easily cultured from acutely infected joints, but in chronic infections viable organisms may no longer be present in lesions. Isolation from the upper respiratory tract is more reliable in chronically infected birds. Mycoplasma can also be directly detected in tissues or culture medium using DNA probes.10,22,27

Mycoplasma synoviae is readily transmitted vertically (through the egg) or horizontally therefore the only effective control is to select chickens or turkeys from specific-pathogen free flocks.27



Gastrocnemius tendon displacement (“slipped tendons”) or perosis is another potential problem in young, growing birds. Perosis may be caused by diets deficient in biotin, folic acid, niacin, or pyridoxine.27


Other potential causes of lameness include “curly toe paralysis”, caused by riboflavin deficiency, pathologic fractures, and rickets. Early in disease, it can be difficult to distinguish lameness from ataxia, so differentials such as Marek’s disease  must also be considered.27



Skin lesions

Knemidokoptes mutans, or the scaly leg mite, can be found in backyard poultry, particularly chickens. This burrowing mite creates crusty, raised lesions are most frequently found on the legs, but can also appear on the comb and wattles.27,43


Poxvirus lesions also occur on unfeathered skin of the legs and face of backyard poultry, especially chickens. These yellow pustules, vesicles, or brown scabs and crust appear quite different from Knemidokoptes. The causative agent is most often fowl pox, but turkey pox can also be encountered.27


Pasteurella multocida can be responsible for localized infection of the wattles, comb, or the subcutaneous tissues of the head.17



Feather loss

Important rule outs for feather loss in gallinaceous birds include:27

      • Ectoparasites
      • Molting
      • Aggressive mating-related trauma
      • Feather destructive behavior

Lice are common parasites in backyard chickens and turkeys (Table 8). Infestations cause rough feathering. When feathers are parted, lice can often be seen scurrying away. Lice eggs can be found as white deposits at the base of feather shafts. Egg clusters or nits can also be palpated, especially over the ventral coelom and near the vent.27

Table 8. Distinguishing lice and mites
Size (mm)1-6 (length)~0.5 (diameter)
Egg locationBase of featherAlong feather shaft

Mites are small, black organisms that resemble ground pepper. Mites often lay eggs along the midshaft of the feather, which appear as blackened areas along the feather shaft. Mites and mite egg-encrusted feathers are particularly noticeable on the ventral coelom and vent.

Treatment options vary for ectoparasites, however ivermectin is commonly used to treat both mite and lice infestations. The chicken mite (Dermanyssus gallinae) feeds on poultry on night and then hides in cracks and crevices during the day, therefore it is also necessary to treat the environment.27



Ophthalmic disease

Important differentials for conjunctivitis in backyard fowl include:27

The ocular form of Marek’s disease causes blue-to-gray discoloration of the iris, usually in birds less than 14 weeks of age.27



Peracute or acute death

When confronted with a complaint of sudden death in backyard fowl, important differentials include:


Forming a differential diagnosis list for the gallinaceous bird follows the same principles as in any other species, however some diseases are relatively unique, or at least much more common, in this taxonomic group. The minimum database frequently includes fecal parasite testing (flotation and saline preparation), hematology, plasma biochemistry, and survey radiographs. Serologic tests and culture can also be used to detect various disease agents. Also keep in mind that is easy for poultry owners to medicate their birds before seeking help. This can butt the diagnostic picture and make recovery of the disease agent more difficult.27

Be sure to consider the health of the entire flock and to remain vigilant for important poultry disease. Although the majority of small flocks appear to pose little risk of disease transmission because they are maintained in semi-isolation13, there is a potential for backyard flocks to play a role in the spread of infectious diseases within poultry populations as well as the transmission of zoonotic diseases to humans.40




  1. Alber A, Stevens MP, Vervelde L. The bird’s immune response to avian pathogenic Escherichia coli. Avian Pathol. 2021 Feb 12:1-10. doi: 10.1080/03079457.2021.1873246. Epub ahead of print. PMID: 33410704.
  2. Barbosa EV, Cardoso CV, Silva RCF, et al. Ornithobacterium rhinotracheale: An update review about an emerging poultry pathogen. Vet Sci. 2019 Dec 27;7(1):3. doi: 10.3390/vetsci7010003. PMID: 31892160; PMCID: PMC7157751.
  3. Basler C, Nguyen TA, Anderson TC, Hancock T, Behravesh CB. Outbreaks of human Salmonella infections associated with live poultry, United States, 1990-2014. Emerg Infect Dis. 2016 Oct;22(10):1705-11. doi: 10.3201/eid2210.150765. PMID: 27649489; PMCID: PMC5038410.
  4. Belkhiria J, Hijmans RJ, Boyce W, Crossley BM, Martínez-López B. Identification of high risk areas for avian influenza outbreaks in California using disease distribution models. PLoS One. 2018 Jan 31;13(1):e0190824. doi: 10.1371/journal.pone.0190824. PMID: 29385158; PMCID: PMC5791985.
  5. Bertran K, Lee DH, Pantin-Jackwood MJ, et al. Pathobiology of clade H5Nx high-pathogenicity avian influenza virus infections in minor gallinaceous poultry supports early backyard flock introductions in the Western United States in 2014-2015. J Virol. 2017 Oct 13;91(21):e00960-17. doi: 10.1128/JVI.00960-17. PMID: 28794040; PMCID: PMC5640860.
  6. Blakey J, Crispo M, Bickford A, Stoute S. Fowl cholera and acute heart rupture in a backyard turkey. J Vet Diagn Invest. 2019 May;31(3):390-394. doi: 10.1177/1040638718823850. Epub 2019 Jan 13. PMID: 30636539; PMCID: PMC6838699.
  7. Blakey J, Stoute S, Crossley B, Mete A. Retrospective analysis of infectious laryngotracheitis in backyard chicken flocks in California, 2007-2017, and determination of strain origin by partial ICP4 sequencing. J Vet Diagn Invest. 2019 May;31(3):350-358. doi: 10.1177/1040638719843574. Epub 2019 Apr 11. PMID: 30973073; PMCID: PMC6838712.
  8. Boodhoo N, Gurung A, Sharif S, Behboudi S. Marek’s disease in chickens: a review with focus on immunology. Vet Res. 2016 Nov 28;47(1):119. doi: 10.1186/s13567-016-0404-3. PMID: 27894330; PMCID: PMC5127044.
  9. Boulianne M, Blackall PJ, Hofacre CL, et al. Pasteurellosis and other respiratory bacterial infections. In: Swayne DE, Boulianne M, Logue CM, et al (eds). Diseases of Poultry, 14th ed. Ames, IA: Wiley & Sons; 2019: 831-889.
  10. Brochu NM, Guerin MT, Varga C, et al. Demographic characteristics, and husbandry and biosecurity practices of small poultry flocks in Ontario, Canada. Avian Dis. 2021 Feb 16. doi: 10.1637/aviandiseases-D-20-00108. Epub ahead of print. PMID: 33592104.
  11. Brochu NM, Guerin MT, Varga C, et al. A two-year prospective study of small poultry flocks in Ontario, Canada, part 2: causes of morbidity and mortality. J Vet Diagn Invest. 2019 May;31(3):336-342. doi: 10.1177/1040638719843575. Epub 2019 Apr 11. PMID: 30973078; PMCID: PMC6838713.
  12. Brown VR, Bevins SN. A review of virulent Newcastle disease viruses in the United States and the role of wild birds in viral persistence and spread. Vet Res. 2017 Oct 26;48(1):68. doi: 10.1186/s13567-017-0475-9. Erratum in: Vet Res. 2017 Nov 16;48(1):77. PMID: 29073919; PMCID: PMC5659000.
  13. Burns TE, Kelton D, Ribble C, Stephen C. Preliminary investigation of bird and human movements and disease-management practices in noncommercial poultry flocks in southwestern British Columbia.
    Avian Dis. 2011 Sep;55(3):350-7. doi: 10.1637/9646-010411-Reg.1. PMID: 22017030.
  14. Cadmus KJ, Mete A, Harris M, et al. Causes of mortality in backyard poultry in eight states in the United States. J Vet Diagn Invest. 2019 May;31(3):318-326. doi: 10.1177/1040638719848718. PMID: 31084344; PMCID: PMC6838705.
  15. Chatziprodromidou IP, Arvanitidou M, Guitian J, et al. Global avian influenza outbreaks 2010-2016: a systematic review of their distribution, avian species and virus subtype. Syst Rev. 2018 Jan 25;7(1):17. doi: 10.1186/s13643-018-0691-z. PMID: 29368637; PMCID: PMC5784696.
  16. Chowdhury S, Hossain ME, Ghosh PK, et al. The pattern of highly pathogenic avian influenza H5N1 outbreaks in South Asia. Trop Med Infect Dis. 2019 Nov 27;4(4):138. doi: 10.3390/tropicalmed4040138. PMID: 31783701; PMCID: PMC6958390.
  17. Christensen JP, Bisgaard M. Fowl cholera.  Rev Sci Tech. 2000 Aug;19(2):626-37. doi: 10.20506/rst.19.2.1236. PMID: 10935284.
  18. Clothier KA, Kim P, Mete A, Hill AE. Frequency, serotype distribution, and antimicrobial susceptibility patterns of Salmonella in small poultry flocks in California. J Vet Diagn Invest. 2018 May;30(3):471-475. doi: 10.1177/1040638718755418. Epub 2018 Feb 6. PMID: 29405899; PMCID: PMC6505821.
  19. Derksen T, Lampron R, Hauck R, Pitesky M, Gallardo RA. Biosecurity assessment and seroprevalence of respiratory diseases in backyard poultry flocks located close to and far from commercial premises. Avian Dis. 2018 Mar;62(1):1-5. doi: 10.1637/11672-050917-Reg.1. PMID: 29620463.
  20. Dimitrov KM, Ferreira HL, Pantin-Jackwood MJ, et al. Pathogenicity and transmission of virulent Newcastle disease virus from the 2018-2019 California outbreak and related viruses in young and adult chickens. Virology. 2019 May;531:203-218. doi: 10.1016/j.virol.2019.03.010. Epub 2019 Mar 22. PMID: 30928699.
  21. Elkhoraibi C, Blatchford RA, Pitesky ME, Mench JA. Backyard chickens in the United States: a survey of flock owners. Poult Sci. 2014 Nov;93(11):2920-31. doi: 10.3382/ps.2014-04154. Epub 2014 Sep 5. PMID: 25193256.
  22. Ferguson-Noel N, Armour NK, Noormohammadi AH, El-Gazzar M, Bradbury JM. Mycoplasmosis. In: Swayne DE, Boulianne M, Logue CM, et al (eds). Diseases of Poultry, 14th ed. Ames, IA: Wiley & Sons; 2019: 907-965.
  23. Food and Agriculture Organization, (FAO). Biosecurity for highly pathogenic avian influenza: Issues and options. FAO Animal Production and Health Paper No. 165. 2008. Available at Accessed August 8, 2021.
  24. Goebel SJ, Taylor J, Barr BC, et al. Isolation of avian paramyxovirus 1 from a patient with a lethal case of pneumonia. J Virol. 2007 Nov;81(22):12709-14. doi: 10.1128/JVI.01406-07. Epub 2007 Sep 12. PMID: 17855523; PMCID: PMC2168997.J Virol 81:12709–12714, 2007.
  25. Gowthaman V, Kumar S, Koul M, et al. Infectious laryngotracheitis: Etiology, epidemiology, pathobiology, and advances in diagnosis and control – a comprehensive review. Vet Q. 2020 Dec;40(1):140-161. doi: 10.1080/01652176.2020.1759845. PMID: 32315579; PMCID: PMC7241549.
  26. Greenacre CB. Reproductive diseases of the backyard hen. J Exot Pet Med. 2015 Apr;24(2):164-171. doi: 10.1053/j.jepm.2015.04.004. Epub 2015 Apr 8. PMID: 32288683; PMCID: PMC7106171.
  27. Greenacre CG, Morishita CY. Backyard Poultry Medicine and Surgery: A Guide for Veterinary Practitioners, 2nd ed. Hoboken, NJ: Wiley Blackwell; 2021.
  28. Hauck R, Mays J, Dunn JR, Shivaprasad HL. Two cases of Marek’s disease in backyard turkeys. Avian Dis. 2020 Sep 1;64(3):347-351. doi: 10.1637/aviandiseases-D-19-00177. PMID: 33205183.
  29. Huang AS, Carvallo FR, Pitesky ME, Stoute S. Gastrointestinal impactions in backyard poultry. J Vet Diagn Invest. 2019 May;31(3):368-370. doi: 10.1177/1040638719843966. Epub 2019 Apr 11. PMID: 30973086; PMCID: PMC6838716.
  30. Kang Y, Li Y, Yuan R, et al. Phylogenetic relationships and pathogenicity variation of two Newcastle disease viruses isolated from domestic ducks in Southern China. Virol J. 2014 Aug 12;11:147. doi: 10.1186/1743-422X-11-147. PMID: 25117968; PMCID: PMC4254411.
  31. Lotfi AR, Abdelwhab EM, Hafez HM. Persistence of Histomonas meleagridis in or on materials used in poultry houses. Avian Dis. 2012 Mar;56(1):224-6. doi: 10.1637/9519-090910-ResNote.1. PMID: 22545550.Avian Dis 56(1):224-226, 2012.
  32. McDougald LR, Cervantes HM, Jenkins MC, Hess M, Beckstead R. Protozoal infections. In: Swayne DE (ed). In: Swayne DE, Boulianne M, Logue CM, et al (eds). Diseases of Poultry, 14th ed. Ames, IA: Wiley & Sons; 2019: 1192-1254.
  33. Morishita TY. Clinical assessment of gallinaceous birds and waterfowl in backyard flocks. Vet Clin North Am Exot Anim Pract. 1999 May;2(2):383-404. doi: 10.1016/s1094-9194(17)30129-9. PMID: 11228736.
  34. Nolan LK, Vaillancourt JP, Barbieri NL, Logue CM. Colibacillosis. In: Swayne DE, Boulianne M, Logue CM, et al (eds). Diseases of Poultry, 14th ed. Ames, IA: Wiley & Sons; 2019: 770-830.
  35. Papp Z, Clark RG, Parmley EJ, et al. The ecology of avian influenza viruses in wild dabbling ducks (Anas spp.) in Canada. PLoS One. 2017;12(5):e0176297. Published 2017 May 5. doi:10.1371/journal.pone.0176297.
  36. Pires AFA, Peterson A, Baron JN, et al. Small-scale and backyard livestock owners needs assessment in the western United States. PLoS One. 2019 Feb 14;14(2):e0212372. doi: 10.1371/journal.pone.0212372. PMID: 30763403; PMCID: PMC6375643.
  37. Ruhnke I, Cowling G, Sommerlad M, Swick R, Choct M. Gut impaction in free-range hens. Proc 26th Aust Poultry Sci Symp; 2015; Sydney, New South Wales. Available at Accessed on July 30, 2021.
  38. Sabater González M, Calvo Carrasco D. Emergencies and critical care of commonly kept fowl. Vet Clin North Am Exot Anim Pract. 2016 May;19(2):543-65. doi: 10.1016/j.cvex.2016.01.007. Epub 2016 Mar 2. PMID: 26948266; PMCID: PMC7110600.
  39. Singleton DA, Ball C, Rennie C, et al. Backyard poultry cases in UK small animal practices: Demographics, health conditions and pharmaceutical prescriptions. Vet Rec. 2021 Apr;188(7):e71. doi: 10.1002/vetr.71. Epub 2021 Jan 28. PMID: 33835557.
  40. Smith EI, Reif JS, Hill AE, et al. Epidemiologic characterization of Colorado backyard bird flocks. Avian Dis. 2012 Jun;56(2):263-71. doi: 10.1637/9865-072811-Reg.1. PMID: 22856180.Avian Dis 56(2):263-271, 2012.
  41. Smith G, Dunipace S. How backyard poultry flocks influence the effort required to curtail avian influenza epidemics in commercial poultry flocks. Epidemics. 2011 Jun;3(2):71-5. doi: 10.1016/j.epidem.2011.01.003. Epub 2011 Feb 16. PMID: 21624777; PMCID: PMC3105326.
  42. Sobhakumari A, Hargrave SA, Hill AE, Poppenga RH. Lead contamination in backyard chicken layer flocks in California. J Vet Diagn Invest. 2019 May;31(3):359-363. doi: 10.1177/1040638718792046. Epub 2018 Jul 20. PMID: 30029577; PMCID: PMC6838708.
  43. Sreedevi C, Ramesh P, Mala Kondaiah P, Lakshmi Rani N, Abhishek M. Occurrence of Knemidokoptes mutans and Laminosioptes cysticola in backyard poultry in India. J Parasit Dis. 2016 Dec;40(4):1627-1630. doi: 10.1007/s12639-015-0673-1. Epub 2015 Mar 14. PMID: 27876998; PMCID: PMC5118299.
  44. Swayne DE, Suarez DL, Sims LD. Influenza. In: Swayne DE, Boulianne M, Logue CM, et al (eds). Diseases of Poultry, 14th ed. Ames, IA: Wiley & Sons; 2019: 210-256.
  45. Swelum AA, Elbestawy AR, El-Saadony MT, et al. Ways to minimize bacterial infections, with special reference to Escherichia coli, to cope with the first-week mortality in chicks: an updated overview. Poult Sci. 2021 May;100(5):101039. doi: 10.1016/j.psj.2021.101039. Epub 2021 Feb 11. PMID: 33752065; PMCID: PMC8010699.
  46. Syed MA, Ullah H, Tabassum S, et al. Staphylococci in poultry intestines: a comparison between farmed and household chickens. Poult Sci. 2020 Sep;99(9):4549-4557. doi: 10.1016/j.psj.2020.05.051. Epub 2020 Jun 26. PMID: 32867999; PMCID: PMC7598113.
  47. Tenzin T, Wangdi C, Rai PB. Biosecurity survey in relation to the risk of HPAI outbreaks in backyard poultry holdings in Thimphu city area, Bhutan. BMC Vet Res. 2017 Apr 21;13(1):113. doi: 10.1186/s12917-017-1033-4. PMID: 28431524; PMCID: PMC5401348.
  48. Tobin MR, Goldshear JL, Price LB, Graham JP, Leibler JH. A framework to reduce infectious disease risk from urban poultry in the United States. Public Health Rep. 2015 Jul-Aug;130(4):380-91. doi: 10.1177/003335491513000417. PMID: 26346104; PMCID: PMC4547567.
  49. US Food and Drug Administration: Animal & Veterinary (2012). CVM guidance for industry #209 ‐ the judicious use of medically important antimicrobial drugs in food‐producing animals. Available at Accessed August 9, 2021.
  50. Varga C, Guerin MT, Brash ML, et al. Antimicrobial resistance in fecal Escherichia coli and Salmonella enterica isolates: a two-year prospective study of small poultry flocks in Ontario, Canada. BMC Vet Res. 2019 Dec 21;15(1):464. doi: 10.1186/s12917-019-2187-z. PMID: 31864357; PMCID: PMC6925488.
  51. Wang XX, Cheng W, Yu Z, et al. Risk factors for avian influenza virus in backyard poultry flocks and environments in Zhejiang Province, China: a cross-sectional study. Infect Dis Poverty. 2018 Jun 19;7(1):65. doi: 10.1186/s40249-018-0445-0. PMID: 29914558; PMCID: PMC6006748.
  52. Winter S, Lechapt E, Gricourt G, et al. Fatal encephalitis caused by Newcastle disease virus in a child. Acta Neuropathol. 2021 Jul 25. doi: 10.1007/s00401-021-02344-w. Epub ahead of print. PMID: 34304282.
  53. Yadav JP, Tomar P, Singh Y, Khurana SK. Insights on Mycoplasma gallisepticum and Mycoplasma synoviae infection in poultry: a systematic review. Anim Biotechnol. 2021 Apr 10:1-10. doi: 10.1080/10495398.2021.1908316. Epub ahead of print. PMID: 33840372.


Further reading

Absalón AE, Cortés-Espinosa DV, Lucio E, Miller PJ, Afonso CL. Epidemiology, control, and prevention of Newcastle disease in endemic regions: Latin America. Trop Anim Health Prod. 2019 Jun;51(5):1033-1048. doi: 10.1007/s11250-019-01843-z. Epub 2019 Mar 15. PMID: 30877525; PMCID: PMC6520322.

Amarasinghe GK, Ayllón MA, Bào Y, et al. Taxonomy of the order Mononegavirales: update 2019. Arch Virol. 2019 Jul;164(7):1967-1980. doi: 10.1007/s00705-019-04247-4. PMID: 31089958; PMCID: PMC6641539

Assen AM, Walkden-Brown SW, Stillman M, Alfirevich S, Gerber PF. Comparison of tracheal and choanal cleft swabs and poultry dust samples for detection of Newcastle disease virus and infectious bronchitis virus genome in vaccinated meat chicken flocks. PLoS One. 2021 Apr 16;16(4):e0247729. doi: 10.1371/journal.pone.0247729. PMID: 33861761; PMCID: PMC8051787.

Ayala AJ, Yabsley MJ, Hernandez SM. A review of pathogen transmission at the backyard chicken-wild bird interface. Front Vet Sci. 2020 Sep 24;7:539925. doi: 10.3389/fvets.2020.539925. PMID: 33195512; PMCID: PMC7541960.

Bavinck V, Bourna A, van Boven M, et al. The role of backyard poultry flocks in the epidemic of highly pathogenic avian influenza virus (H7N7) in the Netherlands in 2003. Prev Vet Med. 2009 Apr 1;88(4):247-54. doi: 10.1016/j.prevetmed.2008.10.007. PMID: 19178969.Prev Vet Med 88(4):247-254, 2009.

Bello MB, Yusoff K, Ideris A, et al. Diagnostic and vaccination approaches for Newcastle disease virus in poultry: The current and emerging perspectives. Biomed Res Int. 2018 Aug 5;2018:7278459. doi: 10.1155/2018/7278459. PMID: 30175140; PMCID: PMC6098882.

Bertzbach LD, Conradie AM, You Y, Kaufer BB. Latest insights into Marek’s disease virus pathogenesis and tumorigenesis. Cancers (Basel). 2020 Mar 10;12(3):647. doi: 10.3390/cancers12030647. PMID: 32164311; PMCID: PMC7139298.

Bethonico Terra MT, Pacheco WJ, Harrison M, McCrea BA, Hauck R. A survey of coccidia and nematodes in pastured poultry in the state of Georgia. Avian Dis. 2021 Mar 1. doi: 10.1637/aviandiseases-D-20-00120. Epub ahead of print. PMID: 33647964.

Blake DP, Marugan-Hernandez V, Tomley FM. Spotlight on avian pathology: Eimeria and the disease coccidiosis. Avian Pathol. 2021 Apr 20:1-5. doi: 10.1080/03079457.2021.1912288. Epub ahead of print. PMID: 33823695.

Carrisosa M, Jin S, McCrea BA, et al. Prevalence of select intestinal parasites in Alabama backyard poultry flocks. Animals (Basel). 2021 Mar 26;11(4):939. doi: 10.3390/ani11040939. PMID: 33810349; PMCID: PMC8066009.

Correia-Gomes C, Henry MK, Reeves A, Sparks N. Management and biosecurity practices by small to medium egg producers in Scotland. Br Poult Sci. 2021 Aug;62(4):499-508. doi: 10.1080/00071668.2021.1894635. Epub 2021 Mar 17. PMID: 33611987.

Cox GJ, Griffith B, Reed M, et al. A vaccine to prevent egg layer peritonitis in chickens. Avian Dis. 2020 Oct 30. doi: 10.1637/aviandiseases-D-20-00093. Epub ahead of print. PMID: 33125038.

Delabouglise A, Thanh NTL, Xuyen HTA, et al. Poultry farmer response to disease outbreaks in smallholder farming systems in southern Vietnam. Elife. 2020 Aug 25;9:e59212. doi: 10.7554/eLife.59212. PMID: 32840482; PMCID: PMC7505654.

Dimitrov KM, Bolotin V, Muzyka D, et al. Repeated isolation of virulent Newcastle disease viruses of sub-genotype VIId from backyard chickens in Bulgaria and Ukraine between 2002 and 2013. Arch Virol. 2016 Dec;161(12):3345-3353. doi: 10.1007/s00705-016-3033-2. Epub 2016 Aug 31. PMID: 27581808.

Garber TL, Hill G, Rodriguez J, et al. Non-commercial poultry industries: surveys of backyard and gamefowl breeder flocks in the United States. Prev Vet Med. 2007 Jul 16;80(2-3):120-8. doi: 10.1016/j.prevetmed.2007.01.012. Epub 2007 Mar 6. PMID: 17337307.

Gonzales Viera OA, Crossley B, Carvallo-Chaigneau F, et al. Infectious bronchitis virus prevalence, characterization and strain identification in California backyard chickens. Avian Dis. 2021 Jan 5. doi: 10.1637/aviandiseases-D-20-00113. Epub ahead of print. PMID: 33400768.

Hardy MC, Robertson SA, Sidge J, et al. Notes from the field: Environmental investigation of a multistate salmonellosis outbreak linked to live backyard poultry from a mail-order hatchery – Michigan, 2018. MMWR Morb Mortal Wkly Rep. 2019 Jan 4;67(5152):1430-1431. doi: 10.15585/mmwr.mm675152a5. PMID: 30605449; PMCID: PMC6334824.

Jhung MA, Nelson DI; Centers for Disease Control and Prevention (CDC). Outbreaks of avian influenza A (H5N2), (H5N8), and (H5N1) among birds–United States, December 2014-January 2015. MMWR Morb Mortal Wkly Rep. 2015 Feb 6;64(4):111. PMID: 25654614; PMCID: PMC4584850. Available at Accessed August 7, 2021.

Lee DH, Torchetti MK, Killian ML, Berhane Y, Swayne DE. Highly pathogenic avian influenza A(H7N9) virus, Tennessee, USA, March 2017. Emerg Infect Dis. 2017 Nov;23(11):1860–3. doi: 10.3201/eid2311.171013. Epub 2017 Nov 17. PMID: 28880836; PMCID: PMC5652434.

Lister SA. Opportunities and challenges in backyard poultry health and management. Vet Rec. 2021 Apr;188(7):262-264. doi: 10.1002/vetr.371. PMID: 33835555.

Morishita TY. Common infectious diseases in backyard chickens and turkeys (from a private practice perspective). J Avian Med Surg 10(1):2-11, 1996.

Susta L, Segovia D, Olivier TL, et al. Newcastle disease virus infection in quail. Vet Pathol. 2018 Sep;55(5):682-692. doi: 10.1177/0300985818767996. Epub 2018 Apr 16. PMID: 29661124.

Zorman Rojs O, Dovč A, Krapež U, et al. Detection of laryngotracheitis virus in poultry flocks with respiratory disorders in Slovenia. Viruses. 2021 Apr 19;13(4):707. doi: 10.3390/v13040707. PMID: 33921858; PMCID: PMC8072874.


To cite this page:

Pollock CG, Morishita TY. Backyard poultry primer. Aug 7, 2021. LafeberVet web site. Available at