The Psittacine Beak and Feather Disease (PBFD; engl. for "feather and beak disease of parrots") is a highly contagious, non-curable and often fatal viral infection in parrot birds (psittacids, parakeets and parrots). It is the most common viral disease in parrot birds in Germany and now affects not only large parrots, but also budgies and other small parrot birds. PBFD is also common among wild parrots. The first description of the circovirus was made on psittacids from the southern Pacific region. Has now been found in many other species. For the long-winged parrot, considered the most endangered African large parrot species, this disease is one of the population-threatening factors along with habitat loss  .
Cause and development of the disease
The causative agent of PBFD is the Beak and Feather disease virus (BFDV) from the virus family Circoviridae. These are small, 12-21 nm large, non-enveloped DNA viruses. Circoviruses are very highly contagious. They have a high tenacity in the environment. Are only transmitted by a few disinfectants (z. B. Glutaraldehyde) safely inactivated.
Several species of circoviruses also occur in other orders of birds (fowl, pigeons, canaries), but they are specific and not transmissible between orders, so a budgerigar cannot contract circovirus from a pigeon.
Infection occurs by oral ingestion of the virus or via aerogenic droplet infection. Due to the high tenacity, indirect transmission through inanimate vectors (cage furniture, clothing, claw clippers, etc.) is also possible.) is possible. The incubation period, i.e. the period from infection to the actual disease, can last for months or even years. Therefore, there is a very high risk of introducing the disease into an aviary when animals are purchased.
After infection, the viruses spread in the blood (viremia) and settle in the organs of the lymphatic system, in the feather follicles and the skin, as well as in the esophagus and crop. Cell death (necrosis) occurs in these organs. Infected birds excrete the virus through crop secretions, feces, and skin and feathers.
PBFD is usually determined by blood test or freshly pulled feathers with the polymerase chain reaction by detection of virus DNA. In a few special laboratories this is also possible via fecal samples.
Nestlings and often also young birds show a peracute course without the typical symptoms in older animals. In these birds, the infection with diarrhea and exhaustion is usually fatal after a short illness, without changes in feathers and beak.
In older animals the disease progresses more slowly. Due to the damage of the feather follicles, there is a loss of cover and wing feathers, brittle or constricted feather shafts and persistent feather sheaths (these are tube-like sheaths around the developing feathers, which normally tear when the feathers grow out, causing the feather to unfold). The feathers can be easily pulled out. May show color changes. Changes in plumage become more pronounced from molt to molt. On the other horn formations (claw, beak) there is excessive growth with a soft brittle horn.
Due to the infestation of the lymphatic organs (thymus, bursa fabricii), there is a reduction in the number of white blood cells (leukopenia) and thus a reduced immune defense, so that the infected birds often suffer from secondary infections. The immunodeficiency usually leads to death 6 to 24 months after the visible onset of the disease.
In adult birds, the disease can also be completely asymptomatic. These animals are dangerous pathogen excretors for flocks.
The diagnosis can be made on the basis of the clinical picture in case of a typical course of the disease. The pathogen can be detected by PCR on plucked out, freshly regrown feathers.
A therapy of the PBFD is not possible. The young birds usually die before treatment can take effect. In older birds, one can try to keep the bacterial and mycotic (air sac mycosis) secondary diseases under control and support the immune system through optimal housing conditions, optimal feeding and the avoidance of stress.
Since therapy is not very promising, prophylaxis is of particular importance. The most important measures are a quarantine of at least 90 days for new purchases with control examination, strict isolation of sick animals and regular disinfection of rooms, aviaries or cages in flocks.
M. Circovirus infection in parrots. Parakeets- A disease with strongly increasing importance. Kleintier konkret 7 (3)/2003, S.