What is proventricular dilatation syndrome?
Proventricular dilatation disease (PDD) is a condition affecting the nerves that supply the gastrointestinal tract of birds, especially the proventriculus or true stomach. Nerves supplying other organs may also be affected, and in some cases, encephalitis (inflammation of the brain) may occur.
First recognized in the early 1970's, PDD was originally called "Macaw Wasting Disease," as the disease caused a gradual wasting away of macaws. Since that time, the disease has been found to affect more than 50 different species of pet birds. It is found most commonly in Macaws, African Grey parrots, Amazon parrots, Cockatoos and Conures. There are some estimates that 20-35% of all birds are affected.
What causes the condition?
PDD has been linked to the Avian Bornavirus (ABV). After decades of research at several well-respected veterinary schools, the exact cause or initiation of the disease is still not 100% clear. Microscopically, the affected nerves are inflamed with an infiltration of certain types of white blood cells. Environmentally, this virus appears to be fairly unstable and is susceptible to heat, dryness and many disinfectants.
What are the signs of birds affected with PDD?
"No one sign is definitive for the condition."
PDD primarily targets the digestive system and the nervous system. The old name, "Macaw Wasting Disease," aptly describes most affected birds. Affected birds have a lack of appetite, may regurgitate, pass undigested seeds in their feces if they are on a seed-based diet, and exhibit progressive weight loss. Birds with neurologic signs may exhibit depression, weakness, ataxia (the loss of full control of bodily movements), head tremors, and, in rare cases, seizures. No one sign is definitive for the condition; however, PDD should be suspected in birds with chronic unexplained regurgitation, weight loss, neurologic symptoms, and undigested food in the droppings. Not all birds with these clinical signs have PDD, so testing is critical for confirmation.
How is the condition diagnosed?
Clinical signs noted above may suggest a case of PDD. A complete physical examination by an avian veterinarian is a logical start to rule out other problems that may be present. Blood tests (a complete blood cell count and blood chemistry profile) and whole body radiographs (x-rays) should be performed. A barium contrast study (shown here) can be very useful in suspicious cases, as it may demonstrate a dilation of the proventriculus.
There is now a specific polymerase chain reaction (PCR) test for ABV, which can be performed on a small sample of blood and/or a swab of the choana and cloaca (mouth and vent). It is possible to have false negative and, rarely, false positive results on this test.
A tissue biopsy of the crop (which is more accessible and easier to perform) and/or the proventriculus with samples submitted for histopathology, is typically accurate in demonstrating ABV in diseased tissues. A biopsy is a procedure requiring general anesthesia and surgical removal or a section of the crop or proventriculus. False negatives results may occur here also, as the disease does not always show up in every section of either the crop or proventriculus at once.
In cases where the patient has passed away, confirmation of the cause of death by having a necropsy performed and tissues of the crop, proventriculus, ventriculus (gizzard), and brain tissue submitted to an avian pathologist for analysis will be essential to establish the presence or absence of PDD and/or ABV.
"Not all Bornavirus-positive birds show symptoms and not all birds with a dilated proventriculus have ABV."
How do birds acquire the condition?
ABV is shed intermittently is the feces, saliva, and nasal secretions. Therefore, spread of the disease is suspected to be directly from fecal-oral contamination and in the air as an aerosol. Not all birds that are exposed to an infected bird will develop the condition, although the condition can spread through a flock. To be safe, birds diagnosed with PDD should be isolated from healthy birds.
Can the disease be treated?
There is unfortunately no definitive or antiviral treatment for affected birds. Supportive care, including the use of certain NSAIDS (non-steroidal anti-inflammatory drugs), treatment of any secondary diseases, and assisted feeding can be given as needed, but the condition is often times fatal. Positive birds must be separated from healthy birds. Speak to an experienced avian veterinarian for more information on this devastating disease.