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Proventricular dilatation disease (PDD) is a globally distributed, serious disease particularly affecting psittacines (large parrots) like macaws, amazons or grey parrots. In 2008, identification of the previously unknown avian Borna virus (ABV) in birds infected with PDD was achieved for the first time. An etiological relationship could then be proven in infection experiments. PDD either affects the gastrointestinal tract, the central nervous system or both areas. This means, on the one hand, there may be digestive disorders such as diarrhoea, vomiting or regurgitation as well as anorexia and the excretion of undigested seeds in faeces. On the other hand, PDD can manifest itself through neurological dysfunctions like ataxia and coordination disorders, tremor or paresis. Both complexes of symptoms are associated with depression, general weakness and excessive loss of weight. In addition to peracute and acute deaths, especially in older birds, chronic progressions of the disease can also be observed. Moreover, clinically inapparent birds can be infected with the virus. Breeding flocks and new additions should thus be tested for an infection with ABV.
Avian Borna viruses are RNA viruses which show high genetic divergence. A negative result does therefore not entirely rule out PDD, as there may be other virus variants, which have not yet been described, leading to this disease. The safest way to detect an ABV infection requires a combination of antibody and pathogen detection. In some birds, only viral RNA can be detected, in others only anti- ABV antibodies are detectable, while others again react positively on both tests.
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