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New Veterinary Perspectives On PDD

Proventricular Dilation Disease is one of the most well-studied avian diseases. Find out the latest on the disease from the First International Conference on Avian, Herpetological and Exotic Mammal Medicine in Wiesbaden, Germany, held April 2013.

Laurie Hess, DVM
Posted: June 27, 2013, 1:15 p.m. PDT

green-winged macaw
PDD was first seen in macaws in the 1970s, and was called "macaw wasting disease" before it was discovered in other birds.

"Vogel” means bird in German. I learned this and many other interesting facts in April 2013, when I attended the First International Conference on Avian, Herpetological and Exotic Mammal Medicine in Wiesbaden, Germany. I have been to dozens of conferences during my career as a veterinarian over the past nearly 20 years, but this one stood out as one of the best. Not only did I have the chance to hear more than a hundred talks on all sorts of avian, reptilian and small mammal diseases and treatments, I also got the opportunity to share ideas with veterinary colleagues from 58 different countries. It was truly an extraordinary experience to hear both what kinds of exotic pet problems veterinarians in different geographic regions face compared with what I deal with in New York, as well as the varied ways in which different vets treat these problems.

Despite the uniqueness of some the diseases seen by veterinarians in different locations, there were some discussions of illnesses that are universally seen by veterinarians worldwide. Among these, talk about one serious avian disease — Proventricular Dilation Disease (PDD) — really stood out. Perhaps one of the most widely studied diseases currently in avian medicine, PDD is caused by a virus that attacks nerves that go to the intestinal tract and stomach in birds. There are two parts to the avian stomach: the glandular part (proventriculus) where digestive enzymes are secreted, and the muscular grinding part (ventriculus or gizzard). With PDD, the virus causes inflammation of the nerves supplying the proventriculus, and sometimes the ventriculus and intestines, decreasing their ability to contract normally to digest food. Thus, food does not pass normally through the intestinal tract, often leading to vomiting and weight loss. The virus can also attack nerves that go to the wings and legs, leading to imbalance and inability to fly or stand. While veterinarians have tried all sorts of treatments —  anti-inflammatory medications, anti-viral drugs, vitamins and other supplements — ultimately this disease is fatal. The incubation period (i.e., time between exposure to the virus and when signs of infection are seen) can be years long. Not all infected birds actually show signs of disease, but can spread it to other birds through infected droppings and oral secretions.

Proventricular Dilation Disease has been a recognized disease since the late 1970s, where it was first seen in macaws that wasted away and died (hence PDD’s original name, "macaw wasting disease”). But the fact that a virus in the Bornavirus family causes inflammation of nerves, leading to signs of disease, was determined only over the last few years. What was most interesting to hear at the German conference is that research has recently demonstrated that inflammation of nerves in PDD caused by infection with bornavirus is actually due to an autoimmune reaction similar to that seen in Guillain–Barré syndrome (GBS) in people.

In GBS, people suffer an ascending paralysis, with weakness beginning in feet and hands and progressing towards the trunk. It sometimes leads to changes in sensation or pain and potentially life-threatening complications if the respiratory muscles are affected. Just as is suspected with PDD in birds, signs of GBS are often triggered by an as yet incompletely characterized infection (possibly with a bacteria or virus) that sets off an autoimmune reaction. Several other serious diseases in people — type 1 diabetes, lupus, multiple sclerosis, rheumatoid arthritis, and others  — are also suspected to be caused by some type of underlying infection (e.g., bacterial, viral, or other organism) leading to an autoimmune response. These diseases are obviously as hotly researched in human medicine as PDD is in avian medicine.

The recognition that PDD is an autoimmune-mediated disease may ultimately help veterinarians find treatments that lessen signs of the disease by decreasing the autoimmune response. Ideally, advances in the understanding of human autoimmune diseases will aid in our understanding of avian autoimmune conditions, as well. Perhaps collaborative research not only between veterinarians across the globe but also between veterinary and human medical researchers will help us all to better understand, treat, and ideally prevent these horrible debilitating diseases in both animals and people in the future.

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New Veterinary Perspectives On PDD

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Reader Comments
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stephanie, north smithfield, RI
Posted: 7/2/2013 1:06:40 PM
I would be more sanguine about the future of treatment for PDD, had I not just lost my 4th bird (in 18 years) to PDD. It was not that the loss was a unexpected -- for 18 years, each day, I have expected deaths.

It was the after symptoms appeared that scared me. It took some jockeying around about what was wrong with this bird -- "We don't see PDD much any more". I was honestly surer than the vet, when Casey first showed symptoms that the problem was PDD.

It disturbs me when I daily hear people describe the symptoms their bird showed before it died, and they are so similar to what I have seen.

It seems to me that the "test" for PDD has allowed both bird owners and the veterinary establishment to slack on this disease. Without tissue extraction (either on a live or dead bird) any diagnosis or lack thereof, is problematic.

The current test is used like it means something. And it might if a positive result occurred. However, it still, unless recently changed, tests 2 of 7 strains of Avian bornavirus, and those 2 strains were chosen by statistical probability. There have been deaths in parrots with other strains than the 2, where tissue sample necropsy showed the lesions typical of PDD. There have been birds with one of the 2 strains that never showed symptoms.

And veterinarians seemed to have stopped advising the expensive tissue sample necropsy when innocent owners don't know to ask for it. In fact, it probably never occurs to most owners that PDD could be the cause, because the emphasis on this disease has cooled since the test was released.
Mary (Terri), Sandia, TX
Posted: 6/30/2013 9:52:31 AM
very good article
n, n, TN
Posted: 6/28/2013 9:52:27 AM
Thank you for the well written article.
Craig, Kalamazoo, MI
Posted: 6/28/2013 8:58:52 AM
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