This unpleasant and to all intents and purposes fatal disease of the parrot family was once thought to be limited to macaws, hence one of its more common names of macaw wasting syndrome. It is also known as, amongst other things as psittacine wasting syndrome and neuropathic gastric dilation. Most commonly, it is known in veterinarian circles as PDD. It is in theory communicable to any psittacine, but is most commonly found in macaws, cockatoos and conures (more often called parakeets).
Signs and Symptoms of PDD
There are wide ranging symptoms of Proventricular dilatation disease and they would appear at first sight to be so different that the owner of the bird may suspect that different diseases may be present at the same time. If two birds are affected – see below for how contagious PDD is considered to be – then they might easily present with completely different symptoms. The most common symptoms appear to be digestive, in that regurgitation, either intermittent or constant is often noticed. This can be as well as undigested food being noticed in the faeces, or may occur as a single symptom.
Weight loss is almost certain to be noticed with either of the preceding, and the bird may appear to be depressed. Taking the digestive symptoms further, the bird may present with constipation, proventricular impaction or diarrhoea. Other symptoms of a more general systemic nature may include hypotension, profuse urine excretion, lethargy and weakness. When the central nervous system is involved the bird may suffer from ataxia so severe that it may fall from its perch. It may also exhibit atypical head movements and fits. These neurological symptoms may be alongside the gastric ones, or can occur alone. From this, it is clear that PDD is extremely difficult to diagnose.
How serious is Psittacine Wasting Disease?
Since the disease was isolated in the late 1970s, no bird which has been diagnosed with it has survived. Some work has been done recently on using non-steroid anti-inflammatory drugs and this has had mixed success. As PDD can have an incubation period of a few weeks to over eight years and can develop at very different speeds once it is diagnosed, the efficacy of any drug will take a long while to establish.
Non-steroidal anti-inflammatory drugs
Meanwhile, early signs are that the use of NSAIDs (Non-steroidal anti-inflammatory drugs) can at least slow down the development of the disease into its fatal stage. As there is as yet no easy diagnosis and no reliable cure, so there is no well-documented study on a large population to show how PDD spreads. Some aviaries can encounter one isolated individual suffering from it, with no other birds catching it, but with such a long incubation period, this is clearly very difficult to determine. In others, the spread has been fast and catastrophic. This suggests that some birds have an innate resistance; forming antibodies after suffering from the disease at a sub-acute level does not seem to fit with the fact that so far all diagnosed birds have died.
Diagnosis of Proventricular Dilatation Disease
Because of the many and varied symptoms and their severity, it is usually only possible to diagnose PDD by biopsy, looking for muscle wasting in the smooth muscle of the gut, or friability in the stomach wall. Ultrasound can also be used to see if the crop is distended, although this is not a symptom found solely in this condition. The symptoms can be caused by poisoning, microbial infection, tumours, parasites and intestinal obstructions to name but a few and because the causative organism has not been isolated, it is as yet impossible to perform a blood test which will give a definitive diagnosis.
Is Proventricular Dilatation Disease a danger to other birds?
Although in the captive population PDD seems to be limited to the psittacines and even then mostly to macaws, cockatoos and parakeets, there is anecdotal evidence that free ranging birds as diverse as Canada Geese, Toucans, Spoonbills and Weavers have shown the characteristic lesions in the gut and also the more obvious behavioural problems such as weakness and severe muscle ataxia. It has been found in the wild on all continents except Europe, but the problem still remains of easy and 100% reliable diagnosis.
Work which has been done has been on relatively small populations and a controlled environment is difficult, with the added problem of the long incubation of this disease. It is possible that this is a mutation of something previously known to science, but as yet it is unknown. As the parrot family in general becomes a more popular choice as pet, being long lived and relatively easy to care for, this disease will probably come to be apparently more widespread.
Prevention of PDD
Unfortunately with the knowledge currently available, there is no way of being certain that your new bird does not have Proventricular Dilatation Disease. Scrupulous attention to hygiene and the general quarantine of new birds into the country are about the only steps that can be taken at this point. Buying from a trusted dealer will minimise the risks and regular contact with your bird will prevent its suffering unnecessarily from unnoticed symptoms.
From the details above, it is clear that the symptoms can be extremely distressing, although the fact that they can all be caused, severally or together, by a whole range of other conditions and problems can lead to a period when the owner will try methods tried and tested on other birds in his care, which worked on simple conditions, such as a mild obstruction or a bacterial infection. If an owner feels that a bird may be suffering from PDD it is a wise precaution to isolate it; although this has not been proved to make any difference, it is always good animal husbandry practice to keep a sick animal away from its companions, if only to give it a calm and stress free environment while it is feeling ill.