Infectious diseases in birds – part 1

Circoviruses, which cause psittacine beak and feather disease (PBFD), are distributed worldwide and infect numerous species such as macaws, agapornids, grey parrots, amazons and parakeets. Signs and prognosis depend on age, immune status and bird species. Nestlings usually die peracutely, while fledglings have an acute course. In budgerigars, mainly young birds in moult are affected. Feather dystrophy may partly disappear after the next moult. Adult birds often show no signs, but frequently remain infected and can also shed the virus. Clinically, acutely infected birds become lethargic, lose appetite and suffer from vomiting and/or diarrhoea; death may occur within 1 – 2 weeks.

In chronic disease, changes occur in the developing feathers. They are often of poor quality, not developing beyond the feather quill and then break off. If the disease lasts longer, there are also changes in the keratin layer of the beak and claws and it can be noticed that the birds have fractured, black and shiny beaks. As the immune system is weakened, a chronic course often leads to secondary infections (e.g. aspergillosis). The virus is mainly transmitted horizontally. PBFD viruses are stable in the environment for up to 18 months and are primarily transmitted via feather dust. However, the virus is also shed with the faeces, especially in diarrhoea. Nestlings can be infected very early by crop feeding of the adults. Vertical transmission is possible as well. Freshly plucked quills as well as EDTA whole blood (in acutely infected birds) are suitable as sample material for the PCR test. The disease cannot be cured, only supportive treatment is possible, especially if there are secondary infections.

Avian polyomaviruses (APV), such as the budgerigar fledgling disease virus (BFDV), are highly contagious pathogens and the causative agent of a disease known as French moult. In addition to budgerigars, many other parrot species are susceptible to the virus, although the disease is usually limited to nestlings. The virus replicates in the cells of the growing feathers, the skin, liver, spleen, tubular renal epithelium, heart and cerebellum. If signs and symptoms occur, they appear 10 – 14 days after infection. Due to generalised haemorrhage, moderate to massive hepatic necrosis and glomerulopathy, induced by immune complexes, infections in nestlings are usually fatal. In adult birds, septicaemia and hepatitis are seen. In chronic cases, feather malformation and inability to fly occur; affected animals usually hop or run around. Adult birds can become infected, but usually do not fall ill. As asymptomatic carriers, they may shed the virus and might even be able to eliminate it from the body after a few weeks. Infected birds can shed the virus for several weeks to months.

Budgerigars are considered the reservoir, as they shed the virus for up to 6 months, with reduced viral shedding over time. Transmission occurs through inhalation of virus-containing particles from feather dust and faeces. Suitable sample materials are EDTA whole blood (at the beginning of the infection), cloacal swabs (during the infection, until the end) and freshly plucked quills (in chronic disease).

Psittacid herpesvirus 1 (PsHV-1), which causes Pacheco’s disease, is an important disease in parrots that can affect both individual birds as well as entire flocks with hundreds of birds. The clinical case depends on the genotype or serotype and the affected psittacine species. In budgerigars and cockatiels, mild to subclinical cases with virus shedding are reported. In large parrots, such as macaws, amazons, cockatoos or grey parrots, infection often leads to death. If there are any symptoms, they are usually non-specific and include anorexia, apathy and poorly developed plumage. Changes in faeces and an increase in uric acid excretion may occur, too. Occasionally, CNS symptoms are observed. Outbreaks of this disease occur particularly in stressful situations, e.g. capture and quarantine of imported birds, change of owner, ­hospitalisation, at the beginning of breeding season and the onset of sexual maturity. In addition to PsHV-1, there are also other herpesviruses in parrots and cockatoos that cause papillomas in the throat and the cloaca. Nevertheless, the herpesvirus PCR provided by Laboklin can detect these as well as the Pacheco’s virus. Carriers shed the virus through the mucous membranes in the head and the cloacal area; during viraemia, the virus can also be detected in the blood. Depending on the stage of disease and the shedding, suitable sample materials are EDTA whole blood, dry cloacal swabs and feathers. For Pacheco’s virus, Laboklin also offers serological testing in heparin plasma or serum in a partner laboratory.

Chlamydia, including Chlamydia psittaci (ornithosis/psittacosis), are intracellular bacteria and cause both respiratory (with and without conjunctivitis) and gastrointestinal signs. The cardinal sign of gastrointestinal disorders is lime-green faeces, also possible regurgitation and vomiting, peracute death may occur. Chlamydia are transmitted by airborne particles, which originate in faeces, feather dust or mucus from the respiratory tract. If there is an outbreak, strict hygiene is required, e.g. it should be avoided to exchange bowls between cages and aviaries. Psittacosis is a zoonosis and can easily be transmitted from birds to humans as well as to other domestic animals. Immunocompromised people and pregnant women should therefore avoid contact with infected birds.

In addition to the peracute form of the disease, there are also chronically ill animals and asymptomatic carriers in which the disease can suddenly relapse. These asymptomatic carriers can cause infestation rates of 10 – 40% in breeding facilities and, thus, pathogens may spread unnoticed. Chlamydia are usually only shed intermittently, so for a reliable detection in birds, it is recommended to take multiple samples (faeces and/or cloacal swabs) at intervals of several days (it is possible to submit pooled samples to Laboklin). Repeat testing is recommended after a few weeks or if signs appear. Serological testing for chlamydia in heparin plasma or serum can be done. If antibodies are detected, it indicates that the animal has had contact with the pathogen. As it is an intracellular pathogen, it is, unfortunately, not possible to grow a culture in combination with an antibiogram.

Ellen Schöner