Approach to the passerine relies on the same concepts of “One Medicine” used as in all animals (Fig 1). Nevertheless many of the infectious agents diagnosed in songbirds are relatively unique to this taxonomic group, or at least much more prevalent when compared to parrots or birds of prey.
Below you will find a collection of differential diagnoses for common clinical problems observed in the passerine. These abbreviated lists should in no way replace professional judgment when evaluating your patient. This “cheat sheet” is merely designed as an aide or reminder system and should never be used for diagnostic decision-making.
Fluffed and ruffled
Rule-outs for the fluffed and ruffled songbird include:
- Atoxoplasmosis (juvenile)
- Chlamydiosis *
- Egg binding
- Poxvirus, septicemic form
- Yersinia pseudotuberculosis
* When compared to psittacines, passerines are less susceptible to Chlamydiosis. Signs of chlamydial infection in songbirds are often non-specific and mortality rates are low.
Atoxoplasma sp., formerly called Lankestrella, is an Isospora type coccidian parasite with a prolonged life cycle. Life stages involve the intestinal mucosa, mononuclear cells, and macrophages. Atoxoplasma has been described in a wide variety of passerines, but it is one of the most important infections of young canaries (Serinus spp.) between 2-9 months of age. Atoxoplasma also affects European finches such as the goldfinch, siskin, greenfinch, and bullfinch. Among zoo collections, this organism has been a documented problem in Bali mynah (Leucopsar rothschildi) fledglings.
The primary mode of transmission of Atoxoplasma is the fecal-oral route. Sporozoites invade intestinal epithelial cells, mononuclear cells, and then disseminate throughout the body. Infected adult birds can intermittently shed large numbers of oocysts for long periods of time. Clinical signs frequently include a fluffed and ruffled appearance and diarrhea. Neurologic deficits may be observed in up to 20% of affected birds, and up to 80% ultimately die.
Antemortem diagnosis of atoxoplasmosis is difficult. Oocysts are shed intermittently and the organism may be missed on fecal exam, even when samples are collected over several days. Other diagnostic tests can include buffy coat smears as well as liver biopsy or splenic aspirate. Definitive diagnosis often relies on identifying the parasite on impression smears of the intestinal tract. Atoxoplasmosis is also called “thick liver disease” and common gross necropsy findings include hepatomegaly and splenomegaly with pinpoint, necrotic foci. The pancreas may be edematous and the intestinal tract is often fluid filled.
Treatment of atoxoplasmosis is also challenging since the organism is resistant to sulfa drugs. Medications that have been tried with variable degrees of success (or failure) include sulfachlorpyridazine (Vetisulid, Boehringer-Ingelheim), toltrazuril (Baycox, Bayer), and diclazuril (Clinicox, Huevepharma). Management relies upon routine, scrupulous sanitation.
Diseases of the chick
Important diseases of juvenile songbirds include:
- Polyoma virus
Avian polyoma virus (APV) can cause sudden death in 2-3 day old chicks, particularly Gouldian finches (Chloebia gouldiae). In older chicks, APV can cause poor feather quality and an abnormal, tubular beak. Gross necropsy lesions can include a pale liver, splenomegaly, and hemorrhage.
Disease of the gastrointestinal tract
Important causes of ingluvitis in the songbird include:
- Salmonella typhimurium var Copenhagen has been associated with granulomatous ingluvitis in European finches
Box 1. Causes of diarrhea in passerines
|Box 1. Causes of diarrhea in passerines|
|Parasite||Atoxoplasma sp.||Canaries, European finches, Bali mynah|
|Cochlosoma sp.||Bengalese (or Society) finches||Maldigestion diarrhea|
|Isospora canaria||Canaries of all ages||Diarrhea|
|Bacteria||Campylobacter fetus var jejuni||Tropical finches (Estrildidae)||“popcorn” feces|
|Enterobacteriaceae (E. coli)||Canaries, finches||Hemorrhagic enteritis in nestlings|
|Mycobacterium avium||Red hooded siskins|
|Fungi||Avian gastric yeast (Macrorhabdus ornithogaster)||Diarrhea, depression, weight loss in the face of a voracious appetite|
Pseudotuberculosis or yersiniosis is caused by Yersinia pseudotuberculosis. Pseudotuberculosis causes non-specific signs of illness and peracute mortality in finches and canaries and is most commonly observed during the winter months. Necropsy findings can include enteritis, liver and spleen absceses, catarrhal pneumonia, and typhlitis. Impression smears of affected organs reveales many rod-shaped bacteria. Research suggests that the best empirical treatment is enrofloxacin (Haesebrouck 1995), however collect samples for culture/sensitivity testing. The incidence of pseudotuberculosis is minimized by stressing sanitation and rodent control.
Box 2. Ophthalmic diseases of passerines
|Box 2. Ophthalmic diseases of passerines|
|Virus||Paramyxovirus type 1||Weaver finches||Diarrhea|
|Poxvirus, septicemic form||Canaries||Conjunctivitis, blepharitis|
|Bacteria||Staphylococcus spp., Streptococcus spp.||Conjunctivitis|
|Other||Cataract||Norwich and Yorkshire canaries|
Box 3. Some important causes of respiratory disease in passerines
|Box 3. Some important causes of respiratory disease in passerines|
|Virus||Poxvirus, wet form||Canary, finch, house sparrow||Dyspnea|
|Poxvirus, septicemic form|
|Parasite||Sternostoma tracheacolum (tracheal mite)||Canary, Australian finches|
|Toxoplasma gondii||Prevalent in Australia|
|Bacteria||Enterococcus faecalis||Tracheitis, pneumonia, air sacculitis|
|Mycobacterium avium||Red hooded siskin|
|Mycoplasma spp.||Canary, finches|
|Fungi||Aspergillus spp.||Mynah bird|
|Metabolic disease||Iron storage disease||Mynah bird|
Among passeriforms, canaries and house sparrows (Passer domesticus) are most susceptible to poxvirus. All three forms of pox may be seen in passerines:
- Dry or cutaneous
- Wet or diptheritic
Canary pox can be devastating, causing mortality in up to 100% of affected birds. The clinical picture can range from non-specific signs of illness, such as lethargy and a fluffed and ruffled appearance, to dyspnea or conjunctivitis, blepharitis, and epiphora.
Early necropsy findings can include cloudy air sacs, pneumonia, necrotizing bronchitis. Later stages exhibit proliferative skin lesions and intracytoplasmic inclusions or Bollinger bodies are found on impression smears.
There is no treatment for poxvirus, and aggressive supportive care is required. Survivors of the septicemic form of disease can develop lung tumors. A vaccine for canary pox is available.
Potential causes of neurologic deficits in passerine birds include:
- Listeriosis (torticollis, tremors, stupor, paresis, and paralysis); canaries particularly susceptible)
- Paramyxovirus III (torticollis)
- Toxic exposure
The most common serotype of paramyxovirus (PMV) observed in passerines is PMV-3. Paramyxovirus type 3 has been isolated from canaries, finches, and weaver finches (family Estrildidae). Clinical signs can include anorexia, weight loss, diarrhea, neurologic signs like torticollis, dyspnea, and conjunctivitis. Gross necropsy reveals only mild, non-specific lesions. Diagnosis relies upon serology or viral isolation.
Causes of dermatologic disease in the passerine bird include:
- Bacterial dermatitis (Staphylococcus spp., Streptococcus spp.)
- Feather cysts (Norwich, Crested and Crest-bred canaries)
- Fiber constriction of extremities
- Fungal dermatitis
- Knemidokoptes mites
- Papillomavirus (bullfinches, chaffinches)
- Polyoma virus (poor feather quality, abnormal tubular beak)
- Straw feathers (canaries, zebra finches)
Causes of sudden death can include:
- Polyoma virus (adult finches after transport and other stressors OR 2-3 day old chicks, especially Gouldian finch )
- Poxvirus (canaries, house sparrows)
- Toxic exposure
- Yersinia pseudotuberculosis (finch, canary)
Forming a differential diagnosis list for the passerine bird follows the same principles as in any other species, however some diseases are relatively unique to this taxonomic group. Also, keep in mind that several conditions are best identified at necropsy by impression smear, so be sure to routinely perform this procedure on major organ systems at every songbird necropsy.