Diseases and conditions

Proventricular Dilatation Disease (PDD)

This disease is seen mostly in species of parrots and parakeets. The disease is considered to develop after infection with the bornavirus.

Although it is most common in young birds, older birds can also develop the disease. The clinical signs are caused by damage to the brain and to the nerves of the glandular stomach, gizzard and upper part of the small intestine.  The muscle activity decreases in these organs and the organs themselves stretch out and become weak.

Because of the diminished peristaltic activity of the stomach muscles, the food isn’t propelled to further sections of the gastrointestinal tract. Infected birds will start to vomit, undigested seeds can be found in the faeces and the birds become very thin and listless. The symptoms can occur within 3 weeks of being infected, although the signs are sometimes only noticed years after being exposed to the virus.


Besides the signs directly caused by the damage of the nervous system, birds are also much more susceptible to secondary infections. One problem is that the crop is filled for a long period of time due to the poor food passage to the glandular stomach. This can lead to ‘sour crop’ or candidiasis. Diarrhoea is another associated problem that can be seen, as bacteria or fungi can flourish in the weakened bird. They can multiply quickly because food doesn't digest well enough in the intestines, providing them with more nutrients than in a healthy bird.

In addition to the nerves in the gastrointestinal tract, other nerves in some bird species can also be affected. Birds can become weak in the legs if the spinal cord or the leg nerves are damaged. If the disease reaches the brain, birds can get problems with keeping their balance,  get a twisted neck and even become paralysed.



There are several methods to detect the virus. DNA testing of the blood is one way of revealing the virus. Another method is to measure the antibodies that the bird produces as a result of the viral infection.

The advantage of these tests is that they will also show the virus in birds that are not yet (visibly) ill. This can be very important in preventing the disease from spreading within an aviary or in the household.


If a bird dies of the disease, a probable diagnosis can be made by examining the internal organs.

Biopsies can be taken from the muscles and the glandular stomach, which are then examined under a microscope. An assessment can then be made of the condition of the nerves. If these are absent in large part, the diagnosis can be made. In a deceased bird, this procedure is quite straightforward. A biopsy can also be obtained if the bird is alive, but this does give the added risk of general anaesthesia and an operation.


If the bird is still alive, radiographs can be made that will show an elongated, enlarged glandular stomach. If more radiographs are taken at intervals, it is also possible to detect if the emptying of the glandular stomach is delayed. Should this be the case, diagnosis is very probable, but not 100% certain. Other conditions or diseases may also show theses signs, for example tumours that partly block the entrance of the glandular stomach.




At present, there is no known treatment for this disease. However, supportive treatment can help to improve the condition of the bird. This consists of removing any blockages. Thereafter, softer or liquefied food can be given to the bird, making the digestive passage easier. Pellets also tend to be easier for birds to digest than seeds. In addition to modifying the food, it is important to check whether the bird has any other infections. These also require treatment.


Considering the fact that PDD is a progressive disease, prognosis is poor.