THE MERCK VETERINARY MANUAL
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Viral Diseases of Pet Birds

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Avian Polyomavirus

(Papovavirus, Budgerigar fledgling disease, Psittacine polyomavirus)

Avian polyomavirus (AVP) primarily affects young birds. It is a primary infectious cause of nestling psittacine mortality, especially in mixed collections and open aviaries. The typical presentation is a well-fleshed juvenile, just prior to fledgling age, with acute onset of lethargy, crop stasis, and death within 24–48 hr. Subcutaneous hemorrhages are often noted when injections are administered. Asymptomatic adults may be carriers. Prevalence of the virus in adult psittacines, including budgerigars, is thought to be high.

Gross necropsy findings in deceased chicks often include pale skeletal musculature and subcutaneous ecchymotic hemorrhages. The kidneys and liver are enlarged and may be pale, congested, and mottled, or have pinpoint, white foci. Petechial or ecchymotic hemorrhages may also be present on viscera, particularly the heart. The heart is sometimes enlarged and may show hydropericardium. Intranuclear inclusion bodies are often seen in the liver, kidneys, heart, spleen, bone marrow, uropygial gland, skin, feather follicles, etc. DNA probe testing of blood and of choanal and cloacal swabs from live birds are also commonly performed.

Aviary control methods include avoiding the housing of budgerigars or lovebirds on premises where other species are bred, adhering to standard hygiene procedures, preventing access to the nursery by visitors, and not introducing birds into the aviary without 90 days quarantine and testing.

Pet store prevention should include separating neonates from different sources, purchasing birds from sources where polyomavirus testing and vaccination are performed, and ideally, not purchasing or selling unweaned birds.

Testing involves collection of cloacal and choanal swabs for PCR testing for viral shedding and blood for virus-neutralizing antibody to identify birds with previous viral exposure.

A vaccine is available. For breeding birds, 2 doses of the vaccine are administered at a 2-wk interval; this should be done off-season. The manufacturer recommends administration of the first dose to neonates when the chick is >35 days of age, with a booster vaccination in 2–3 wk.

Cloacal Papillomatosis

(Internal papillomatosis)

Cloacal papillomatosis is associated with a herpesvirus of the strain that also causes the acute presentation of Pacheco's disease (see Pacheco's Disease). Papillomatosis tends to occur as a flock problem, particularly in breeding colonies of macaws and Amazon parrots. Prolapsed cloacal tissue is erythematous and originates from the inside rim of the cloaca. Spread to the mouth and upper GI tract may occur. Surgical removal (surgical resection, electrocautery, cryosurgery, or radiosurgery) or chemical cautery (ie, topical silver nitrate) is indicated but cannot be regarded as a permanent cure. Relapses may occur from year to year, and autogenous vaccines may or may not be helpful. Multiple resections can be performed, but sequelae include stricture and secondary cloacal infections, notably Escherichia coli and Clostridium spp.

Psittacine Beak and Feather Disease

Psittacine beak and feather disease (PBFD) is caused by a psittacine circovirus. The name is not representative of the current typical clinical presentation, which does not include beak abnormalities and is less likely to have the severe, classic feather abnormalities that were seen in cockatoos when the disease was first documented. PCR screening has greatly decreased the prevalence of the virus in captive bred Cacatua spp. Disease is still noted, however, in African Grey parrots, Eclectus, lovebirds (Agapornis), lorikeets, and other species. This debilitating infection may affect any psittacine, although Old World species are much more susceptible, and it has been reported in wild and domestic birds. The natural infection appears to occur primarily in juvenile birds, with few instances of clinical infection seen in birds >3 yr old.

Typical findings include feather loss, abnormal pin feathers (constricted, clubbed, or stunted), abnormal mature feathers (blood in shaft), and lack of powder down in applicable species. Pigment loss may occur in colored feathers. Immunosuppression is present. Acute infection in chicks also occurs, with several days of depression followed by profound changes in the developing feathers and sudden death.

Diagnosis is based on gross appearance, plasma PCR, and biopsies of affected feather follicles showing basophilic intracytoplasmic inclusions. PCR may detect infection in birds that still appear healthy. These birds may subsequently become ill, or may mount an effective response to the virus. Quarantine and retesting are recommended for PCR-positive, asymptomatic birds.

The contagious nature of PBFD and its generally terminal outcome in clinically affected birds warrant isolation and eventual euthanasia in most clinical cases. Strict hygiene with attention to dust control, screening protocols including PCR testing of both the birds and the environment, and lengthy quarantines are highly recommended in breeding facilities with susceptible species. In infected breeding colonies, removal of all eggs for cleaning and artificial incubation may also be required.

Pacheco's Disease

(Pacheco's herpesvirus)

Pacheco's disease (PD) is a highly contagious, acute disease of psittacines caused by a herpesvirus. It is associated with stress, which can cause clinically healthy carriers to shed virus and initiate infection in susceptible birds. It is spread by direct contact and by aerosol or fecal contamination of food or water. Macaws, Amazon parrots, Monk parakeets, and conures are often involved in outbreaks. Old World species are less likely to be either inapparent carriers or clinically susceptible. Patagonian species and some Aratinga spp may be natural hosts in the wild, and some individuals of these species may asymptomatically shed virus when stressed. Other species can also act as carriers.

Terminal signs include acute death in well-fleshed birds and bright yellow urates with scant feces. Due to the acute nature of the disease, no gross histologic lesions may be evident. Most affected birds, however, will have an enlarged liver, splenomegaly, and renomegaly. The liver may be mottled or grossly discolored. Ecchymotic and petechial hemorrhages may be present on the pericardium and within the mesenteric fat. Primary differential diagnoses for PD include acute salmonellosis, polyomavirus, and psittacine reovirus. Acyclovir (80 mg/kg, tid or 400 mg/kg feed) can be used during an outbreak; however, the risk of increased transmission due to handling is great. Autogenous vaccines have been developed during outbreaks and have proved effective in decreasing morbidity and mortality.

Proventricular Dilatation Disease

(Macaw wasting disease)

Proventricular dilatation disease (PDD) primarily affects macaws, conures, and African Grey parrots, although all parrots and some psittacines are probably susceptible. This condition has recently been associated with bornavirus infection, and PCR testing is being developed. The common presentation of affected birds is chronic weight loss (often following an initial increase in appetite), the passage of undigested food (most easily recognized when whole seeds are found in the droppings), and regurgitation. A dilated proventriculus may be seen radiographically. Neurologic signs (convulsions, tremors, weakness, ataxia, blindness) may occur in some species, with or without concurrent GI signs. Outbreaks are sporadic, with a low morbidity and a high mortality.

Typical histologic findings include multifocal lymphocytic, plasmacytic ganglioneuritis of the proventriculus and portions of the GI tract. PCR testing of choana, cloaca, or fecal swabs confirms the presence of avian bornavirus; serologic assays such as ELISA can also confirm infection. Differential diagnoses include heavy metal intoxication, foreign body obstruction, internal papillomatosis, internal neoplasia, and GI infectious disease (including bacterial and fungal proventricular infections). Clinical pathologic findings are variable, but increased serum CPK and a mild lymphocytosis, monocytosis, or heterophilia may be seen. Proventricular biopsies in affected birds are prone to dehiscence due to low total protein subsequent to malabsorption. Crop biopsies are a less invasive diagnostic tool and may be useful if the sample taken contains sufficient innervation to be diagnostic; however, a negative crop biopsy does not rule out the presence of PDD.

Treatment for PDD includes providing easily digestible foods and may be aided by the administration of an NSAID (eg, meloxicam, celecoxib). In aviaries with confirmed cases of PDD, increased separation of the birds and ventilation of the aviary is recommended to decrease or eliminate this disease.

Other Herpesvirus Infections

Amazon tracheitis is also caused by a herpesvirus, although the frequency of occurrence of this infection is low. Other clinically significant herpesviruses include the strain responsible for papillomatous foot lesions in Cacatua spp and the depigmentation lesions noted on the feet of macaws.

Poxvirus Infections

Because of import restrictions, poxvirus in blue-fronted Amazon parrots is no longer commonly seen. In pet bird practice, veterinarians will generally encounter only canary, lovebird, and pigeon poxviruses, which have specific host ranges.

Three different clinical presentations have been described: 1) Cutaneous, the most common, with discrete papules, pustules, or crusty scabs (depending on the stage of infection) developing on unfeathered areas, such as the face—notably the periorbital area and commissures of the mouth—and the legs and feet. Mortality is low, and the infection usually is self-limiting. 2) Diphtheritic (“wet” form), which may progress from the cutaneous form or present independently. Blepharitis, chemosis, and conjunctivitis are followed by fibrinonecrotic lesions on mucous membranes of the oropharynx, upper respiratory tract, and esophagus. Mortality is often high. 3) Acute onset of generalized signs, including depression, cyanosis, anorexia, and rapid death.

The virus causes eosinophilic, intracytoplasmic inclusion bodies (Bollinger's bodies), which displace the nucleus of epithelial cells and cause cellular swelling. Scarring of eyelids and small opacifications of the cornea are common sequelae, although permanent damage is relatively minor compared with the original lesions.

Diagnosis is by virus isolation and typical histologic findings of epidermal hyperplasia with ballooning degeneration, intraepithelial vesicles, and eosinophilic, intracytoplasmic inclusion bodies.

Parenteral vitamin A, ophthalmic ointments, heat, humidity, parenteral antibiotics, daily cleansing of the affected areas, and attention to diet is recommended. Transmission is via insect vectors (mosquito bites) or other entry through breaks in the skin. Therefore, mosquito control and indoor housing are vital to prevent outbreaks. Vaccines for canarypox and pigeonpox are available, but are specific for their host species.

Viscerotropic Velogenic Newcastle Disease

(Exotic Newcastle disease)

Viscerotropic velogenic Newcastle disease (VVND, see Newcastle Disease and Other Paramyxovirus Infections), caused by a paramyxovirus, affects most avian species and is a significant threat to the poultry industry. Transmission is by respiratory aerosols, fecal contamination of food or water, direct contact with infected birds, and fomites.

Birds may be asymptomatic or die acutely. Signs include depression, anorexia, weight loss, sneezing, nasal discharge, dyspnea, conjunctivitis, bright yellow-green diarrhea, ataxia, head bobbing, and opisthotonos. In prolonged cases, unilateral or bilateral wing and leg paralysis, chorea, torticollis, and dilated pupils also may be seen. Primary differential diagnoses include other paramyxoviruses (non-Newcastle), psittacine proventricular dilatation syndrome, and heavy metal toxicosis.

Lesions include hepatomegaly, spleno-megaly, petechial or ecchymotic hemorrhages on serosal surfaces of all viscera and air sacs, airsacculitis, and excess straw-colored peritoneal fluid. Diagnosis is traditionally via viral isolation but agar gel immunodiffusion tests that can be performed on whole blood or serum are now available.

Only symptomatic treatment is possible and thus not advised. If suspected, VVND must be reported to appropriate authorities. Vaccination is prohibited in birds entering the USA because it does not eliminate the carrier state and hampers viral detection during quarantine.

There are several less pathogenic paramyxovirus strains. Paramyxovirus group 3 is reported most frequently in Neophema spp, lovebirds, and Gouldian finches. Clinical signs may be absent, resulting in acute death. In disease of longer duration, respiratory signs, pancreatitis, and torticollis may occur.

Avian Influenza

Avian influenza is caused by orthomyxoviruses. Due to the zoonotic potential of some strains, and the recent discovery of new mutations, this virus may become a more significant pathogen. Both zoonotic potential and economic effects on the poultry industry are causes for concern. (Also see Avian Influenza.)

Last full review/revision July 2011 by Teresa L. Lightfoot, DVM, DABVP (Avian)

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