Polyomavirus
Polyomavirus can cause disease in both psittacine and passerine species. Feather abnormalities and increased neonatal mortality in budgerigars, and sudden death in young parrots [including amazons, African greys, macaws, eclectus, ring-neck parrots, cockatoos, and conures] and finches have been ascribed to polyomavirus infection. These birds typically are serologically positive and have positive PCR tests on blood and/or cloacal swabs prior to death. Necropsy findings include hemorrhages, hepatomegaly and splenomegaly. On histology, intranuclear inclusion bodies can be seen, but are not necessarily present in all cases. Testing for polyomavirus nucleic acid in tissue (in situ hybridization) may be necessary to confirm the diagnosis.

Clinical disease in adult parrots due to polyomavirus infection is uncommon, although death of adult birds has been described either alone or in conjunction with Chlamydia psittaci or psittacine beak and feather disease virus infection. Adult parrots develop subclinical infections and may subsequently serve as a reservoir of infection through intermittent viral shedding in their droppings. Either a positive antibody titer or a positive PCR test result on whole blood supports viral exposure and/or viremia. Documentation of viral shedding can be done via PCR testing of cloacal swabs. However, shedding may be intermittent and repeated cloacal swab PCR tests may be needed to confirm the presence of a carrier state.

In a closed, polyomavirus-free aviary, testing for polyomavirus should be done prior to the introduction of new birds. The carrier status of new birds should be investigated during quarantine.

Psittacosis
Psittacosis refers to infection of parrots with Chlamydia psittaci. Ornithosis is the same disease in other avian species, and infection in people is referred to as chlamydiosis. (Chlamydiosis is the preferred term and can be used to describe all infections with C. psittaci.) There are numerous strains of C. psittaci that are infective across a wide range of hosts. Many mammals, as well as reptiles and insects, can be infected by C. psittaci.

In parrots, ruffled feathers with lime green droppings (biliverdinuria) and a history of exposure to a new bird is the classical presentation for chlamydiosis. The clinical course usually is several weeks before either death or recovery (resulting in a potential carrier bird), although acute deaths may also occur. Affected birds typically show leukocytosis and an increase in the enzyme aspartate transaminase (AST). Protein electrophoresis usually shows hypoalbuminemia and hypergammaglobulinemia. The diagnosis can be confirmed in a sick parrot with a positive or rising antibody titer, and a positive PCR test from a combined choanal/cloacal swab. In clinically normal parrots, a negative titer and negative PCR test result [on whole blood or combined choanal/cloacal swab] indicates absence of C. psittaci infection. A positive result with either serology or PCR testing in a normal parrot with no increase in either white cells or AST indicates exposure, rather than clinical disease. A carrier state exists in many adult birds which serve as the reservoir for further disease outbreaks. There is no definitive testing to confirm a carrier bird, but a persistent IgG titer is a common finding.

Testing for chlamydiosis should be done prior to introducing new birds to an aviary, and as a screening test for a new pet, breeding bird, and for birds being exposed to ill or immunosuppressed individuals.