Frequently Asked Questions:
Proventricular Dilatation Disease (PDD) and Avian Bornavirus (ABV)
1. What is proventricular dilatation disease (PDD)?
PDD is a fatal disease in birds that is named for one of the presenting symptoms, dilatation of the proventriculus, an organ located in the upper digestive tract that is primarily responsible for secreting digestive enzymes and transferring food from the crop to the gizzard where it can be ground up and digested further. When a bird has proventricular dilatation disease, there is significant damage to the nerves in the upper digestive tract, and it cannot move food efficiently through the different compartments. Food accumulates in the proventriculus, so much that the organ swells (dilates) dramatically. Digestion and food absorption are negatively affected, such that affected birds often regurgitate, pass undigested seeds, and begin to waste and lose muscle tone due to their poorly functioning digestive tract.

Birds with PDD can also exhibit additional symptoms related to damage beyond the digestive tract, in the central nervous system. Decreased function in motor neurons can lead to problems with balance, walking, as well as abnormal head movements and even seizures.

PDD has a varied course of progression; some birds diagnosed with the disease can live for years, while other birds can succumb quite rapidly. Sadly, little is known about what governs the severity of the disease, thus predicting outcomes for any individual bird can be quite difficult.

2. In what species of birds has PDD been observed?
PDD has been most commonly reported in parrots on four different continents and over 50 different species of parrots are known to have contracted the disease including cockatoos, macaws, African grey parrots, pionus, eclectus parrots, conures, cockatiels, and many more. Additional reports suggest that PDD may also infect birds very distantly related to parrots, including the spoonbills, toucans, peregrine falcon, Canadian goose, weavers, and possibly ostriches.

3. How is PDD diagnosed?
For living birds, a combination of clinical history, radiography or fluorography, and crop biopsy tests are used to diagnose the disease. The radiography and fluorography tests assess the size of the upper digestive tract organs and rate of food flow through the digestive tract. Crop biopsies can provide tissue for microscopic analysis. Lymphoplasmacytic infiltration of the neural ganglia that enervate the crop is the hallmark characteristic of PDD (translation: presence of the body?s immune cells in neural tissues where they are normally not present); however this test suffers from lack of sensitivity?a high rate of false negatives.
For deceased birds, clinical history combined with necropsy findings of dilatation in the organs of the digestive tract, and microscopic evidence of lymphoplasmacytic infiltration of the neural ganglia over a wider array of tissues is often sufficient to confer a PDD diagnosis.

4. Is there any treatment or cure for PDD?
There are a number of reports on PDD symptom management that use non-steroidal inflammatory drugs (NSAIDs) and amantadine that show some success in clearing lesions. However, no large-scale trials have been performed, so it remains unclear what the best course of action for PDD-affected birds is. In birds which have returned to normal following treatment, we have previously been unable to determine if they are still carriers of the virus and potentially infectious to other birds. Infected birds, (crop biopsy positive) which appear clinically normal also exist and can be a source of infection for other birds.

5. How is PDD transmitted?
This is unknown. Previous studies and our recent work suggest that PDD might result from a viral infection. Anecdotal reports suggest that an oral-fecal route is likely. Additional studies will be required to determine the exact cause and route of transmission.

6. When did PDD first appear?
PDD was first seen in the 1970?s in an outbreak among wild caught Macaws from Bolivia imported into the U.S. and Germany. It was initially described as Macaw wasting disease.

7. Can people get PDD?
There is no evidence that PDD is transmissible to humans.

8. What is Avian Bornavirus and how is it linked to PDD?
Avian Bornavirus (ABV) is a new member of the bornavirus family of viruses. See below for a further description of bornaviruses. We have demonstrated a strong correlation, or association, between the presence of a set of new novel ABVs and the presence of PDD symptoms in affected birds and the lack of ABV in unaffected birds. Thus infection with ABV is a compelling candidate cause of PDD. We do not have proof at this time that ABV causes PDD. Ongoing experiments are designed to test the hypothesis that the isolated virus can actually cause the disease in a previously healthy bird.

9. How was Avian Bornavirus discovered?
Researchers at UCSF, in collaboration with veterinarians Susan Clubb and Ady Gancz, analyzed the tissues of affected birds with the ViroChip, an advanced diagnostic that has the ability to detect all known viruses in addition to previously uncharacterized viruses.

10. What is a bornavirus?
Bornaviruses are a family of non-segmented single-stranded RNA viruses. They form a unique viral family within the set of non-segmented single-stranded RNA viruses because they possess 3 unusual features: first, they replicate in the nucleus of the cells they infect; second, they utilize pre-mRNA splicing to generate a variety of viral transcripts. The prototype member of this family was detected in a fatal disease of horses, Borna disease that was named for the town of Borna, Germany in which outbreaks of the disease were first described and observed. Borna disease in horses confers encephalomyelitis, ataxia, and behavioral changes, and is typically fatal. Since their discovery in the early 1990s, bornaviruses have been found in a wide variety of mammals and warm-blooded animals and has been implicated in a report of encephalomyelitis in a canine host, a neurological disease in felines known as cat staggering disease. Serological studies have also implicated bornaviruses in a paresis syndrome of ostriches, but to date, this has not been confirmed by virus isolation or sequence recovery.

11. I looked up bornavirus online and found it has links to schizophrenia and mental health disorders in humans. Should people with birds/parrots be concerned that they are at risk for contracting a disease from their pet?
There is no evidence that humans can get infected via their pet bird. Moreover, studies linking bornaviruses to mental health disorders in humans are controversial for two reasons: first, there have been conflicting results from study-study on whether the detection of bornaviruses actually correlates with the disease states, and second, because the human isolates identified to date are very similar to previously described isolates from horse and other animals, it has been questioned in some cases whether the isolates detected in humans were actually false positives due to contamination of specimens with laboratory strains of bornaviruses.

12. My pet has been diagnosed with PDD, how can I get it tested for ABV?
A diagnostic test will be available shortly.

13. My pet has been diagnosed with PDD, how can I participate in further PDD research?
If you would like to participate in ongoing research efforts. Please send a e-mail to our Logistics Manager, Tara Christiansen at

14. All commercial inquires please contact Ha Nguyen in the UCSF OTM office at (415) 353-4461 or e-mail at

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