It has become evident that infection and disease are not synonymous, particularly with this virus. Many birds can be infected with the virus but rarely do adult birds develop disease. They develop sensitized B and T lymphocytes, as well as antibodies and an immune response that prevents disease from occurring and eliminates the viral infection. Those that do show disease often are immunosuppressed. The exception is caique species, where adult birds can develop disease.
Whether disease will develop is dependent on the species of bird infected, the age of the bird infected, and whether that bird is immune-suppressed. Birds that are infected and do not develop disease still have virus replication within their bodies and shed virus in their droppings for a period of time. The length of time that virus shedding occurs, again, depends on the age of the bird at the time of infection and its species. Some hand-fed birds that are partially immune-competent will develop and recover from transient disease. These birds often retain the viral infection for prolonged periods of time and serve to transmit the infection to naïve individuals.
Birds that are infected but do not develop signs of disease will become viremic and may begin shedding virus through the cloaca and possibly oral mucosa. Rarely, viremia lasts for months. Fecal shedding lasts for up to 16 weeks, but again is much shorter in adult birds and nestlings that are infected at an older age.