Avian polyoma virus (APV) was first discovered in 1981. The virus is known to cause acute and chronic illness in multiple bird species. APV causes illness in parrots, while related haemorrhagic polyoma virus causes haemorrhagic nephritis and enteritis in gees. Both diseases are inflammatory and have high death rates in young birds. In this respect APV is different from related mammalian polyoma viruses because its mortality rate is much higher than for example of mammalian polyoma virus SV40. The main symptoms of APV virus infection are hepatitis, ascites and hidropericardium. The mortality can reach 100%. Young birds surviving the disease often develop chronic illness resultingin permanent malformations of feathers. However this is not always the case. These birds are often asymptomatic and represent most common spreaders of the disease as they are normally active and reproduce normally.
APV infects all species of parrots; however it seems to infect more frequently species of macaws, conures, eclectus parrots, lovebirds, cockatiels and budgies. It also infects other species such as finches, eagles and vultures. The virus is ubiquitous around the world. All APV viruses isolated and characterised to date are genetically conserved and there exists only one genotype and serotype of the virus. APV spreads horizontally between adult birds as well as vertically from parents to offspring. Offspring can die in eggs or normally hatch and then die between age of 10th to 14th day or later in age of 20 to 56 days. The chicks die mostly because of the muscle failure. Frequent problem is inability to empty crop which causes the retention of food. In case of survival the chick usually shows less than usual amount of feathers. They usually lack the feathers on their back, chest and flying feathers, but they often have normal feathers on their wings. This condition can improve after a few rounds of moulting.
The main symptoms are:
Less than usual feathering – lacing feathers on back, chest and flying feathers
Delayed emptying of crop – chicks in nests can die with the crop full
Anorexia and loss of weight
Haematoma under the skin
Failure of vital organs (some birds are unable to fly)
The disease is often fatal and therefore not all symptoms may develop.
Spread of disease and prevention
APV is transmitted by bird to bird contact and not from human or other animals. It is usually transmitted by direct contact of two birds, breathing of aerosol, wing dust, secretions, sperm, eggs and food. The virus can also be spread with infected food, water containers, nesting material, poles, other cage equipment, ect. It is often carried from asymptomatic mother or father to the offspring or infects eggs before they are laid. APV stays present and active for some time after the infected bird was removed. Thus the entire place has to be properly cleaned and disinfected. There are several disinfectants available on the market that will destroy the virus. It is important that the infected bird is isolated as soon as we suspect the illness, which prevents further spread of the virus. The bird should be tested for presence of the virus and the rest of birds being in contact should be tested in case of a positive result. It is also recommended to randomly test birds from the rest of the flock, which will help efficiently and quickly limit the development and spread of the disease.
There is no cure for the disease caused by APV; however there is a vaccine which can protect birds against the virus. The vaccine is hard to get and vaccination should be done by the age of 5 weeks (it depends of a type and size of a bird). Because there is no cure for the disease it is important to detect the disease at an early stage as this is the only way to stop the disease from spreading.
There are several tests that can efficiently proof the disease. The most frequently used method is polymerase chain reaction (PCR). The method is used to detect viral DNA in blood or feather pulp. The method is based on amplification of viral DNA in a sample and is non-invasive and therefore friendly to the bird and the owner. Another method used for detection of virus is immunological testing based on ELISA. The method tests host’s immune response; however it has several disadvantages such as: the immune response can vary from bird to bird, the antibodies are present long after the disease is cured and it is less accurate than PCR.