Kevin Roeser, DVM and Jennifer Blair, DVM
Proventricular Dilatation Disease, also known as Wasting Disease or PDD, is an inflammatory neurological condition affecting companion parrots and a number of other bird species. As the cause for this disease was historically poorly understood, this disease has spread throughout much of the avian population since being first reported in the late 1970’s. Current reports estimate that 30-35% of all birds are infected. Recent research has revealed a connection between Avian Bornavirus and clinical disease, and emerging studies have proven a causative relationship in a group of cockatiels. However, more research is still needed to provide information regarding the complete disease process in affected birds. Additional challenges for pet owners and veterinarians alike include highly variable incubation periods (time between infection and development of symptoms), possible carrier states, and lack of reliable and cost-effective methods for identifying and screening for this disease.
This disease primarily affects the gastrointestinal and neurologic systems, and may include weight loss, regurgitation, appetite loss, passage of undigested food items in the feces, depression/lethargy, blindness, seizures, and poor coordination. Less commonly, heart disease and feather-picking or self-mutilation have been reported in relation to PDD.
Specific testing for PDD can be challenging. This is due in part to the fact that not all birds infected with Avian Bornavirus go on to develop clinical PDD. All birds should have a thorough physical examination, a complete blood count (CBC) and a chemistry panel performed to rule out other diseases that can cause similar signs. Radiographs with a contrast media called barium are often performed and may show dilation of the proventriculus (glandular stomach). However, there are several causes for these changes besides PDD. It should also be noted that some affected birds never exhibit manifestations of gastrointestinal disease.
Specific tests for infection with Avian Bornavirus have recently become available. Our current recommendations include submission of both blood and choanal/cloacal swabs for Avian Bornavirus PCR. This test identifies viral genetic material (RNA) in your bird’s blood, feces, or choanal secretions. However, research data has shown that both false negative and positive (rare) results are possible. An antibody test may also become more widely available in the future.
For birds suspected to have active symptoms, analysis of small tissue samples (biopsies) taken from the crop remains the “gold standard” diagnostic. Unfortunately, this diagnostic procedure may yield false negative results in up to 50% of cases. Crop biopsies also require general anesthesia and aftercare associated with minor surgery, and thus are currently not recommend for “screening” bird populations for disease. Lastly, evidence of PDD may also rarely be found upon evaluation of feather biopsies in birds with feather damaging behavior.
Unfortunately, there is no known specific therapy to treat the infectious (viral) cause of this disease process. Instead, our treatment strategies are aimed at addressing secondary inflammation, maintaining gastrointestinal function, and minimizing neurologic symptoms. Treatment varies by individual patient, but may include:
1) Non-steroidal anti-inflammatory medications (NSAIDs): COX-2 selective medications such as meloxicam (Metacam®) and celecoxib (Celebrex®) may promote clinical improvement in affected birds. NSAID medications have the potential for inciting gastrointestinal disease (stomach upset, ulcers) and potentially liver and kidney damage. Baseline bloodwork to evaluate organ function is recommended prior to starting such medications and should be performed at regular intervals during treatment. Long-term, our goal will be to use the lowest effective dose possible for each patient, but many patients require high doses to control their clinical signs.
2) Gastrointestinal motility medications: Medications that stimulate smooth muscle contraction throughout the gastrointestinal tract are used to address regurgitation and impaired motility caused by PDD. Examples of these medications include metoclopramide (Reglan®) and cisapride (Propulsid®).
3) Ginger: This supplement may help to improve GI motility as well as to reduce systemic inflammation. Some birds may not find this supplement to be palatable due to its strong taste. Please use this supplement only as directed by your veterinarian.
4) Antiviral medications: The role of human anti-viral medications in the treatment of PDD has yet to be determined. Recent research has shown no benefits of these medications in psittacine species, but there have been anecdotal reports of clinical improvement in treated birds. Specific antivirals currently being used in pet birds include amantidine and less commonly ribavirin.
5) Gabapentin (Neurontin®): Birds that exhibit seizure activity or evidence of nerve-related pain (i.e. feather damaging/mutilation) may benefit from this medication. Other methods of pain control may be required based upon patient response.
6) Supportive care: Symptomatic therapy must be tailored to the individual bird, but may include variations in perching materials, housing, and diet. Additionally, regular screening for secondary infections (i.e. bacterial or fungal crop or intestinal infections) is recommended.
It is important to note that PDD is not currently a disease that can be cured. Some birds may show symptomatic improvement, but relapses are to be expected. Anecdotal reports suggest that concurrent disease or other stressors (molting, reproductive behavior) may predispose previously affected birds to recurrence of clinical signs.
Our ultimate goal is disease prevention. Avian Bornavirus is a relatively unstable virus, and is susceptible to drying, heat, and presumably routine disinfectants. The virus is intermittently shed in feces, saliva, and nasal secretions. Transmission is usually via fecal-oral route, but may also be due to aerosolization of the virus. Ideally, birds that test positive for Avian Bornavirus should be isolated from other birds. These birds should also be removed from breeding programs, as vertical transmission of the virus from parent to egg is possible.
At this time, there is no solid consensus as to whether we should be testing all new birds for this disease. Because false negatives (and rarely positives) can occur, the value of testing every new bird is questionable. A positive result does not necessarily indicate that infection will develop or that the bird will shed the virus. Regardless, we strongly encourage bird owners to maintain a closed aviary and avoid situations where your birds are exposed to other birds of unknown health status.
Current research is directed at better understanding the pathogenesis of PDD, which in turn should provide better insights into more specific testing and treatment modalities. Our veterinarians will adjust these recommendations as needed as more information becomes available.