Introduction to Polyomavirus
Avian polyomavirus is a very serious disease in birds causing depression, dehydration, and haemorrhaging under the skin. It is of particular interest to anyone who breeds birds in captivity, as most deaths occur in new hatchlings and birds up to five months of age. Older animals can contract it, but they are usually symptom free, and simply become carriers. These carrier birds are a huge risk to breeders, as when they are shedding the virus, they can infect and kill hatchlings within the aviary and beyond.
Symptoms of Polyomavirus
Many birds which die from polyomavirus do so without showing any symptoms. Others will show signs of depression, dehydration, and skin haemorrhaging. They may vomit, have diarrhoea, excessive urine output and even tremors and paralysis. It is because there are so many possible signs of the disease that it is missed in the vital first days, being taken for something else. Yet others will have minor symptoms and appear to recover, only to die sometimes months later by a swift and savage recurrence of the disease.
Young Birds with Polyomavirus
A newly hatched bird with polyomavirus can be born normally and be asymptomatic, and yet can die within a few weeks having failed to thrive. The immune depression and organ failure resulting from the condition will have made food impossible to digest and so in practice the baby bird will have died of malnutrition and dehydration. Other chicks will live longer but will not thrive well; they may have feather abnormalities and swollen abdomens, yet will be well enough to fly and mix with other birds. These youngsters are the dangerous ones as they will be carriers and can decimate an aviary by passing on the polyomavirus.
Diagnosis of Polyomavirus in a Bird
The diagnosis of polyomavirus is very difficult and due to the nature of the disease is, sadly, most often done post-mortem. This is important, though, as it can give a fairly early warning to the breeder, so any chick dying early should be taken for an autopsy. Swabs taken from adult birds or apparently unaffected chicks can be taken to the lab for testing, although because the virus does not necessarily give a positive test even when the bird is actively shedding it, it is not a definite diagnosis either way.
The best that can be said is that positives are definitely positive; a negative might be negative or positive, so should really be considered a ‘maybe’. Other tests available will show if a bird is shedding the virus, but will not otherwise tell if an infection is present. In the absence of a definite raft of diagnostics, a lack of any proven medication against polyomavirus and its almost one hundred per cent mortality in young birds, the only way to contain and control this virus is to be constantly vigilant and keep a scrupulously clean environment.
Prevention of Polyomavirus
As prevention is better than cure, it is well worth while making a few changes to aviary practice to avoid this terrible condition taking over. Eradicating it once it has taken hold is almost impossible, as it can lurk undetected for some while until a carrier bird starts shedding the virus again and the whole cycle is resumed with added virulence. Firstly, all new birds should be checked by the vet and in any event quarantined for a minimum of 30 days. Some authorities suggest that ninety days should be the minimum for certainty of safety, but this may not be practical in all cases.
Cleanliness the Key
When feeding a new clutch, it is vital that the same feeding utensils are not used from nest to nest. Failure to do this is a sure fire way of spreading polyomavirus. When visiting aviaries, or moving between aviaries of your own, it is very important to change shoes and clothing. This may seem rather extreme but because the virus is airborne in dust which can cling, it is necessary to keep any outbreak contained. It is important to remember at all times that birds can be asymptomatic and yet still be highly contagious. The best means of containing and preventing an outbreak of polyomavirus is to keep all breeding aviaries closed units.
This is in most domestic breeding situations impractical, but it is certainly a wise precaution to avoid anyone handling hatchlings or young birds if they have any contact whatsoever with other bird populations. Although keeping the nest boxes and environment clean is a given, it is still very difficult to eradicate the virus, which can even survive treatment with chlorine bleach.
Transference of the Disease
The virus can travel on draughts, clothing, feeding apparatus or it may even be spread as simply as one feather from an infected bird sticking to a visitor’s shoe. Therefore, only constant vigilance can prevent its spread. The most commonly affected birds are psittacines and finches, although other species can be affected by strains of the same virus. The virus does not cross species and cannot affect humans.
Vaccination against Polyomavirus
Vaccination is available, but its efficacy has yet to be proved in a large enough sample. The first dose should be given at the age of four weeks and for increased protection, this does should be double the usual strength. This should then be followed up at six to eight weeks of age. If vaccinating an adult bird for the first time, the first dose should also be a double one, followed by four weeks later by one more. After this initial vaccination, a booster should be given every year as it does not confer permanent immunity.
Cost of dealing with Polyomavirus
This programme could become very costly for a large aviary, but the expense would have to be offset against the financial loss and emotional stresses caused by an outbreak of polyomavirus in a breeding situation. As the virus is very difficult to get rid of once it has a foothold in an aviary, it may be considered worthwhile to try the vaccine, even though it is unproved. This is not a replacement for very careful husbandry – all of the preventative measures above must be carried out on a permanent basis to ensure the safety of all birds of all ages.