Proventricular Dilatation Disease and Avian Bornavirus
Susan Clubb, DVM - Rainforest Clinic for Birds
Proventricular dilatation disease (PDD) has been reported since the late 1970's and has been found in captive parrots worldwide. Initially, the disease seemed to be limited to macaws and was referred to as Macaw wasting syndrome. The disease has now been found in a wide variety of species and is now commonly referred to as Proventricular dilatation disease or psittacine proventricular dilatation syndrome.
In 2007, we were fortunate to work with a cutting edge virology laboratory at the University of California at San Francisco. Working with samples submitted by Dr Clubb as well as an Israeli veterinarian, this lab was able to identify a new virus- Avian Bornavirus, which we now know can cause PDD. Researchers in the US, Europe and the Middle East are working to learn more about Avian Bornavirus and new information is coming available at a rapid rate.
Avian Bornavirus causes PDD by causing inflammation of the brain and nerves. While we don’t know everything about how it is transmitted, we believe that the virus is inhaled or ingested, then moves to the brain. From the brain it moves down the nerves to the ganglia. The virus causes inflammatory cells to invade into the ganglia of nerves and reduces their function. This in turn reduces the proper function of the organs which are innervated by affected nerves. Many organs and systems can be affected, but we usually see it as a neurological disease or a digestive disease as it frequently affects the nerves of the crop, proventriculus, ventriculus, intestines, and adrenal gland. We do know that infected birds shed the virus intermittently in the feces.
PDD has been reported in more than 50 species of parrots - See list below. But PDD is not only a disease of parrots. It has also been reported in Canada Geese, spoonbills, toucans, falcons, weavers and canaries. Oddly PDD has not been reported in budgerigars (common parakeet) and they may be resistant.
Adults are affected more frequently than juveniles and both sexes are affected. PDD has been diagnosed in birds as young as 10 weeks to more than 40 years old.
The most common clinical signs of PDD include depression, weight loss (with or without decreased appetite), constant or intermittent regurgitation, and/or passage of undigested seeds in the feces indicating a malabsorptive or maldigestive disorder. Proventricular impaction, muscle atrophy, abdominal enlargement, lethargy, weakness, polyuria, diarrhea, scant feces and hypotension have also been reported in affected birds. Neurological signs may include ataxia, abnormal head movements, seizures, and motor deficits.
But as we learn more, we know that not all infected birds are clinically ill. We don’t know yet how to predict which infected bird(s) will go to develop clinical disease.
Clinical Diagnosis of PDD
While we now have laboratories which can detect Avian Bornavirus in cloacal swabs and antibodies to Avian Bornavirus in blood, it is important to understand that finding the virus does not mean that an individual bird has clinical disease.
The definitive means of diagnosing PDD is still to find inflamed ganglia on pathologic examination of biopsies in live birds, on in tissues on necropsy. In live birds we routinely do a crop biopsy because this organ is just below the skin making it very accessible. This procedure is rapid and relatively non-invasive. The bird is anesthetized and a small incision is made in the skin over the crop. A small piece of crop tissue is removed and the crop is sutured closed followed by closure of the skin. An antibiotic injection is given to prevent infection. The sutures are absorbable but can be removed after 10 days. Adverse effects of the procedure are uncommon. Pathology results are usually complete in about 2 weeks.
Clinical diagnosis of PDD in ill birds is made by looking at clinical signs as listed above and laboratory findings.
Changes in bloodwork in PDD-affected birds are inconsistent. Hypoproteinemia (low blood protein) hypoglycemia, (low blood sugar) heterophilia (elevated heterophil count) and anemia, have been reported. Fungal or bacterial secondary infections are common in affected birds. An elevation of the enzyme creatinine phosphokinase (CPK) is also suggestive of PDD as an indication of nerve tissue damage.
Radiographs are useful diagnostic techniques. Distension of the proventriculus and increased transit time of barium are common findings. Endoscopic examination may show impaction, ulceration, and dilatation of the proventriculus.
On necropsy examination we find emaciation, pectoral muscle atrophy, and dilatation of the esophagus, proventriculus, ventriculus, or small intestine. The proventriculus may appear thin-walled and distended with food. Bacterial, fungal or tuberculosis infections, parasites, gastrointestinal obstructions, tumors, trauma, maldigestion disorders, toxin ingestion or malnutrition may cause similar changes and also must be considered. Definitive diagnosis must be based on pathology.
When we see this combination of history, clinical signs and laboratory evidence we often make a presumptive diagnosis of PDD. We will then test for Avian Bornavirus preferrably using a combination of blood tests (ELISA test for antibodies) and cloacal swabs (PCR for presence of ABV).
Disease does not develop in all exposed birds, which suggests that some birds have an innate resistance, develop a protective immune response, lack factors that are required for inducing the disease, and possess factors which prevent development of the disease, or develop a carrier state. The disease has subacute, acute and chronic stages; however, the majority of diseased birds die within several months to a year after developing clinical signs if left untreated.
Therapy and prevention
PDD is an inflammatory disease so we treat PDD by using non-steroidal anti-inflammatory drugs, NSAIDS. These drugs (similar to aspirin in action) inhibit the Cox 2 enzymatic system. Celebrex (celecoxib) an anti-inflammatory commonly used for treating arthritis in humans has been used most extensively. Other Cox 2 inhibitors (human and veterinary drugs) are available such as metacam, a commonly used veterinary drug. The duration of treatment needed is not really known and treatment may be required for a year or more. Side effects may include GI bleeding, development of ulcers, and possible allergic reactions. If very dark or black stools develop the drug should be discontinued immediately.
While affected birds improve in condition and may look normal with treatment, we don’t yet know the effects of treatment on viral shedding, so these birds may remain infectious. Birds under treatment should be housed separately from susceptible birds.
We also use Amantadine which is an anti-Parkinson’s disease drug so it helps the bird with problems of coordination. While this drug has some anti-viral effects, we do not know if it will be effective directly against the virus. Rarely do we see an adverse reaction, similar to an allergic response with this drug.
We have developed a 2 part nutritional supplement that is designed to reduce inflammation. We call them our anti-inflammatories. They consist of an oil supplement which is designed to supply needed Omega 3 and omega 6 fatty acids and fat soluble vitamins. It is based on salmon oil, so it’s a bit smelly, but really is good for health. The aqueous supplement contains water soluble vitamins, natural anti-oxidants (Grape seed extract and turmeric) as well as trace minerals, Coenzyme Q 10 (good for the heart), and more. These nutrients work with the drugs to reduce inflammation and speed healing.
Progress should be monitored by clinical improvement, monitoring weight, and repeated viral testing as well as repeated crop biopsies. When monitoring weight in critical birds remember that weight gains can be deceiving. And increase in weight might occur if the intestinal tract is dilating and holding excessive amounts of food.
We have looked extensively at tests which have come available for screening for ABV and have selected 2 tests which we feel are very helpful. One measures antibody in the blood by ELISA. The other detects the RNA of ABV in cloacal swabs. The swab is placed in a special transport medium that protects the virus RNA. Otherwise the enzymes in the feces would degrade the RNA. Ideally with the swab test we would prefer to swab maybe every other day for a week because we know from available research that birds can shed the virus intermittently, however this is not practical for many people. We prefer to run both tests and can do so economically.
Health screening of new birds should include screening for ABV. The best screening would include crop biopsy. We do know that many healthy birds can carry ABV. Screening will help you to protect your established birds from this dreaded disease.
Parrot Species in which Proventricular Dilatation Disease has been Reported
(Pdd has not been reported in Budgerigars - the common parakeet)
Lesser sulphur-crested cockatoo
African Grey Parrot
Timneh Grey Parrot
Red Bellied Parrot
Blue Headed Pionus
White Crowned Pionus
Blue and gold macaw
Orange winged Amazon
Blue fronted amazon
Yellow Crowned Amazon
White fronted Amazon
Double Yellow Headed Amazon
Yellow Naped Amazon
Yellow Lored Amazon
African grey parrot
Timneh African grey
Gold capped conure
Green Cheeked Conure
Peach front conure
Grey Cheeked parakeets
Ring necked Parakeets