What is proventricular dilatation disease?
Undigested seeds passed in the feces, a sign of proventricular disease in birds fed a seed-based diet.
(Photo: Dr. Gregory Rich, DVM)
Proventricular dilatation disease (PDD) is a condition that affects the nerves of the gastrointestinal tract in birds, especially the proventriculus or true stomach. The affected nerves become damaged and stop stimulating the muscles of the digestive tract, so food in the intestinal tract moves very slowly or not at all. Nerves supplying other organs may also be affected, and in some cases, encephalitis (inflammation of the brain) may occur.
First recognized in the early 1970s, PDD was originally called "macaw wasting disease." Since that time, the disease has been found to affect more than 50 different species of pet birds. It is found most often in macaws, African gray parrots, Amazon parrots, cockatoos, and conures. There are some estimates that 20%-35% of all birds are affected.
What causes PDD?
PDD has been linked to avian bornavirus (ABV). Despite decades of research, the exact cause or initiation of the disease is still not clear. Microscopically, the affected nerves are inflamed with an infiltration of certain types of white blood cells. This virus appears to be unstable and is susceptible to heat, dryness, and many disinfectants.
What are the signs of PDD?
PDD primarily targets the digestive system and the nervous system. Affected birds have a lack of appetite, may regurgitate, exhibit progressive weight loss, and pass undigested seeds in their feces if they are on a seed-based diet. Birds with neurological signs may exhibit depression, weakness, ataxia (the loss of full control of bodily movements), head tremors, and, in rare cases, seizures.
No single 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 may suggest a case of PDD. To rule out other problems, it is best to start with a complete physical examination by an avian veterinarian. Blood tests (a complete blood cell count and blood chemistry profile) and whole-body radiographs (X-rays) should be performed. A barium contrast study can be 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 (mouth) and cloaca (vent). It is possible to have false negative and, rarely, false positive results on this test.
A second test has been developed: the avian anti-ganglioside antibody test. This test detects the presence of antibodies against gangliosides, which are lipids found in nerve cells. This test is primarily used to diagnose avian ganglioneuritis (AG), a disease often associated with ABV and PDD. While ABV testing focuses on detecting the virus, the anti-ganglioside antibody test looks for the bird's immune response to the disease, which can be a more accurate indicator of active infection.
Your veterinarian may perform a tissue biopsy of the crop and/or the proventriculus (true stomach), in which they surgically remove tissue samples to send for microscopic examination (histopathology). Tissue biopsy is typically accurate in demonstrating ABV in diseased tissues, although false negatives results may occur, as the disease does not always show up in every section of the crop or proventriculus.
In cases where the bird has passed away, it is essential to confirm the cause of death and establish the presence or absence of PDD and/or ABV by having a necropsy and sending tissue samples from the crop, proventriculus, ventriculus (gizzard), and brain to an avian pathologist for analysis.
How do birds get PDD?
ABV is shed intermittently in the feces, saliva, and nasal secretions, so it is suspected that PDD spreads 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 PDD be treated?
There is unfortunately no definitive or antiviral treatment for birds affected by PDD. Supportive care can be given as needed, including treatment of any secondary diseases, assisted feeding, and nonsteroidal anti-inflammatory drugs (NSAIDS) such as celecoxib or robenacoxib. However, the condition is often fatal. PDD-positive birds must be separated from healthy birds. Speak to an experienced avian veterinarian for more information about this devastating disease.
