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Unlocking the PDD Mystery

Clinician's Brief (Capsule)

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Proventricular dilatation disease (PDD) is an important cause of death in psittacine birds, affecting >50 species, especially cockatiels. Definitive diagnosis requires pathohistologic detection of lymphoplasmacytic infiltrates in the ganglia of the upper GI tract. In 2008, an avian bornavirus (ABV) was isolated from affected birds and limited experimental infections reproduced the disease.

In this study, 18 birds were experimentally infected with ABV and the course of infection evaluated over 33 weeks. Five birds showed typical PDD signs between 33 and 199 days postinfection. Key clinical findings were apathy, undigested seeds in the feces, and epileptic-like seizures. Two apparently unaffected birds died suddenly at days 66 and 120 postinfection. The remaining birds were healthy until the end of the study, at which time they were euthanized. At necropsy a dilated proventriculus was observed in 7 of 18 birds, 4 of which had shown clinical signs consistent with PDD. Histologic examination revealed that all birds had mononuclear infiltrates characteristic of PDD in a range of organs. This study showed that PDD can be reproduced in birds using ABV inoculation and that the course of infection is variable. The presence of antibody titers did not indicate immunity but rather resolving or ongoing infection.

Commentary
Today clinicians still struggle to explain PDD to owners because so much remains unclear, including pathogenesis of infection. The results of this study confirmed that ABV antibody levels are poor predictors of the course of clinical disease. The study also highlighted what is probably the most intriguing aspect of ABV infection: the route of infection and pattern of host immune response seem to influence development of disease, possibly even severity of infection.
—Dominique Keller, DVM, PhD


Source
Pathogenesis of avian bornavirus in experimentally infected cockatiels. Piepenbring AK, Enderlein D, Herzog S, et al. EMERG INFECT DIS 18:234-241, 2012.

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