Zoonotic Avian Infections

Key Points

  • Individuals that work or live with birds may be at risk for zoonotic diseases.
  • Psittacosis in humans may range from asymptomatic infection to flu-like signs to severe disease including pneumonia.
  • The most important route of Salmonella spp. transmission is eating incompletely cooked food and drinks; however humans may also be infected from poultry and free-living birds.
  • Allergic alveolitis is a serious, under-recognized condition, that may affect bird owners after exposure to feather antigen.
  • Most human West Nile virus infections are asymptomatic although mild influenza-like signs may be seen in about 20%. A small proportion (less than 1%) develop more severe neurologic disease which is sometimes fatal.
  • Avian influenza may cause severe disease affecting the respiratory, digestive and/or nervous system and high mortality.
  • As avian veterinarians, we are all on the front line for identifying avian influenza. Train staff to recognize clinical signs and answer questions.
  • Immunocompromised individuals commonly contract Mycobacterium aviuminfection from contaminated soil. Infection from birds is extremely rare.



Also known as parrot fever and ornithosis, psittacosis is caused by Chlamydophila psittaci, an obligate intracellular bacteria of birds. Infected birds shed bacteria through feces and oculonasal discharge. Most human cases result from exposure to infected psittacine birds. Apart from exposure to infected pet birds, individuals at risk include pigeon fanciers, employees in poultry slaughtering and processing plants, veterinarians and technicians, zoo, laboratory and avian quarantine employees, farmers, gamekeepers, and wildlife rehabilitators. Humans can be infected during transient exposure to infected birds and contact may be so brief the patient may forget. Person-to-person transmission has been suggested but not proven.

An average 250 human cases of Chlamydophila psittaci are reported annually in the United States. Clinical signs typically follows a 5 to 14 day incubation period. Disease ranges from subclinical to systemic illness with severe pneumonia. Most people demonstrate sudden onset fever, headache, malaise, and myalgia with a non-productive cough that can be accompanied by breathing difficulty and chest tightness. Splenomegaly and a non-specific rash are also sometimes observed.Chlamydophila can also cause endocarditis, myocarditis, hepatitis, arthritis, keratoconjunctivitis, and encephalitis. Respiratory failure, thrombocytopenia, hepatitis, and fetal death have been reported in pregnant women. Disease is fatal in less than 1% of properly treated humans, however fatality can reach 15% to 20% where antimicrobials are not provided.

Humans exposed to birds with avian chlamydiosis should seek medical attention if they develop flu-like symptoms or respiratory problems. Physicians should consider psittacosis in all ill patients exposed to birds, and early, specific treatment for psittacosis should be initiated. Most states require physicians to report psittacosis cases to public health authorities. Timely diagnosis and reporting can help identify the source of infection and control the spread of disease.

Animal and public health authorities may issue quarantine for all birds on premises where C. psittaci infection has been identified. With the approval of state or local authorities, bird owners may: (1) treat birds in a separate quarantine area, (2) sell birds that have completed at least 7 days of treatment, provided the new owner agrees in writing to continue quarantine and treatment and is informed of the disease hazards, or (3) euthanize infected birds. After completion of treatment or removal of birds, quarantine can be lifted after infected premises are thoroughly cleaned and disinfected.



Salmonellosis is the most common and serious zoonosis of the developed world, with some 5 million Americans affected annually. Although Salmonella spp. are sensitive to many disinfectants as well as cooking, they do survive for extended periods in stagnant water and even longer in soil. Humans typically contract disease by eating incompletely cooked food. Humans may also be infected by exposure to Salmonella spp. shed from poultry or free-living birds, particularly birds roosting at garbage dumps. Salmonellosis typically presents as gastroenteritis, although any organ can be infected. Antibiotic therapy is generally contraindicated in man, as this increases the chances of patients becoming carriers.


Campylobacter infection causes acute enteritis and severe abdominal cramps. The incubation period is 2 to 5 days in humans, and infection is typically self-limiting, lasting 7 to 10 days. Many infected birds become carriers (e.g. 35% of migrating waterfowl and galliformes), although the rate of carrier status is very low in psittacines.


Yersiniosis or pseudotuberculosis is a bacterial infection of birds. Pigeons and doves are the most common avian reservoir. Epizootics can occur in birds, leading to major mortalities and massive environmental contamination. Human infections are common in Europe, but only sporadic in the United States. In humans, incubation is typically 7 to 21 days. The most common form of disease is acute mesenteric lymphadenitis, sometimes with erythema nodosum, an acute, nodular, erythematous eruption usually limited to the lower legs. Severe enteritis can also occur, with approximately 50% suffering from hepatomegaly and jaundice.

Newcastle disease

Newcastle disease is an important infectious disease of poultry. Humans working in close contact with birds such as poultry farmers, slaughterers, and veterinarians can become infected from stock or live vaccine. The incubation period in humans is 1 to 2 days. The most common clinical sign is unilateral or bilateral conjunctivitis, although fever, headache, lethargy, pharyngitis, encephalitis and hemolytic anemia can occur. Illness lasts from 3 days to 3 weeks and recovery is spontaneous.

Allergic alveolitis

Allergic alveolitis is a serious, under-recognized condition, which can affect bird owners after exposure to feather antigen. Acute allergic alveolitis occurs 4 to 8 hours after large-scale exposure, resulting in coughing, dyspnea, and fever. Subacute disease occurs after years of moderate exposure and is characterised by a dry cough and progressive dyspnea. Diagnosis is achieved with intradermal skin testing, and prognosis is good if further exposure to avian antigen can be prevented. The chronic form results from years of low level exposure to feather dander and is most common in pet bird owners. Signs include dyspnea, non-productive cough, rales, and weight loss. Disease is irreversible as the lungs undergo chronic pulmonary fibrosis, but the owner must halt further exposure to prevent further deterioration.

West Nile virus

West Nile virus (WNV) has caused sporadic cases and outbreaks in humans and horses in Europe since the 1960s. First found in North America in 1999, WNV has spread across much of the the Americas since then.

West Nile virus is predominantly an infection of birds and mosquitoes. Virus circulates in the blood of birds, then when mosquitoes take a blood meal from an infected bird they take up the virus as well. The mosquito then transmits the virus to the next bird from which it feeds. Other infected species, such as horses or humans, are incidental victims. West Nile virus is not transmitted from person-to-person, except accidentally after blood transfusion.

The incubation period in man is typically 3 to 15 days. Eighty percent of infected humans are asymptomatic while almost 20% have mild flu-like illness. A small proportion (less than 1%) develop more severe disease such as encephalitis, meningitis, or meningoencephalitis, which is occasionally fatal. Most deaths have been reported in those over 50 years of age.

In temperate zones, WNV occurs in late summer or early autumn. Most mosquitoes that carry WNV are likely to bite around dusk and dawn. When outdoors, particularly during this time of day, wear loose-fitting, light-weight clothing that covers as much skin as possible and use an effective insect repellent on exposed skin and clothing. Reduce mosquito bites indoors with use of air conditioning, insect-proof screens, and insecticides. Bed nets can be used if necessary.

Avian influenza in birds

Avian influenza (AI) naturally circulates in wild waterfowl causing little or no symptoms, however AI may cause severe disease affecting the respiratory, digestive and/or nervous system in many other bird species. Clinical signs may include depression, anorexia, ruffled feathers, diarrhea, ataxia, respiratory distress, and petechia. Outbreaks associated with high bird mortality are called highly pathogenic avian influenza (HPAI).

Large AI outbreaks in poultry have been described in Pennsylvania in 1982 (H5N2), Mexico in 1993 (H5N2), Hong Kong in 1997 (H5N1), and The Netherlands in 2003 (H7N7). In January 2004, AI in poultry was confirmed in Vietnam. Since then, there have been HPAI outbreaks in a number of countries caused by the H5N1 subtype of influenza A virus.

Given the scale of the outbreaks in poultry, the virus does not appear to easily infect humans. Humans are usually infected through close contact with live, infected birds. Birds shed virus in their feces, so contact with feces is also a possible transmission route. There is evidence to support limited human-to-human transmission (which presents the major concern for the future). In the 1997 Hong Kong outbreak there were 18 confirmed human cases with 6 deaths, and in the Netherlands in 2003 there were 83 confirmed mild human cases and 1 death. In the current outbreak of AI, human cases and deaths due to H5N1 have been reported from a number of countries.

Influenza outbreaks with high mortality affecting thousands and sometimes millions of people have occurred in 1918, 1957, 1968, and 1977. These pandemics were caused by new influenza subtypes that were probably formed by combination of avian and human influenza viruses. Emergence of a new, highly pathogenic AI virus with the capacity to infect humans may lead to development of a new subtype that can spread from person-to-person and causes serious disease.

All clinicians should train staff to recognize clinical signs and actions to take when the public phone with questions. Factors to consider are national biosecurity, personal, staff and public health, and prevention of contamination of your facilities. In the United Kingdom, the Department for Environment, Food and Rural Affairs (DEFRA) will only investigate if more than 10 birds are found dead during office hours, at other times and in other situations, avian veterinarians are on the front line.

Infrequent and rare, but potentially serious zoonoses

Cryptococcus neoformans is a saprophytic fungus commonly found in soil contaminated by bird feces, especially pigeon droppings. Disease is rare in birds, but often involves necrotic, granulomatous lesions of the respiratory, gastrointestinal, or nervous system as well as a characteristic pale, gelatinous exudate. Human infection generally occurs through contact with exudates or other infective material and can affect healthy as well as immunocompromised individuals. Always consider cryptococcosis when treating atypical upper respiratory infections in birds.

Mycobacterium avium is worthy of note, only in so far as human tuberculosis is commonly contracted by immunocompromised individuals from contaminated soil. Infection from infected birds is extremely rare. Other rare zoonotic pathogens include Erysipelas, Listeria, rabies virus, Toxoplasma, and Giardia.

In humans, clinical signs of cryptosporidiosis comprise persistent diarrhea, malabsorption, abdominal pain, fever, and vomiting. Although the coccidian parasite, Cryptosporidium, is commonly found in numerous bird species, as of yet no avian strains have been incriminated of causing human disease. However birds can become infected by mammalian strains, so it seems only a matter of time before mammals are infected by avian strains.

Specific control measures recommended for zoonotic infections

To prevent transmission of Chlamydophila psittaci and other infectious agents to humans, specific control measures are recommended:

  • Instruct at risk personnel to wear protective gear and an appropriately fitted respirator with N95 or higher rating when handling birds infected with C. psittacior when cleaning their cages. Surgical masks may not prevent transmission ofChlamydophila. Before performing necropsies, wet carcasses with detergent and water to prevent aerosolization of infectious particles.
  • Encourage pet stores to maintain detailed records of all bird-related transactions for at least 1 year. This will aid in identifying sources of infected birds and potentially exposed persons.
  • Isolate newly acquired, ill, or exposed birds. Also quarantine birds that have left and returned to the site, including those who have been to the vet’s office, shows, fairs, and other events. House quarantined birds in a separate air space for at least 30 days. Test or prophylactically treat birds for psittacosis before adding them to the group.
  • Test all birds of unknown health status (not previously tested or exposed since last test) for psittacosis. This is particularly important prior to hospitalization to minimize the risk of infecting other patients.
  • Maintain good husbandry practices. Position cages to prevent transfer of feces, feathers, food, and other materials from one cage to another.
  • Thoroughly remove organic debris before disinfection. Chlamydophila psittaci is susceptible to most disinfectants and detergents as well as heat, however remember many disinfectants are respiratory irritants and should be used in a well-ventilated area.



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To cite this page:

Forbes N. Zoonotic avian infections. January 29, 2008. LafeberVet Web site. Available at https://lafeber.com/vet/zoonotic-avian-infections/