PDD: Proventricular Dilation Disease

PDD is a disease that causes a failure in the parrot’s digestive system. While it is also called “Macaw Wasting Syndrome”, it is absolutely not exclusive to the macaw.  In fact, it has been seen in many species of our companion birds and their wild counterparts.

So that you can better understand the impact of this disease, first let me describe the parrot’s digestive system:  The bird breaks down food with its beak and passes it down to the crop.  The crop slowly delivers food to a two part stomach.  The first part of the stomach is called the proventriculus, the glandular portion which secretes digestive juices which help to break down food.  The proventriculus is connected to the muscular portion of the stomach called the ventriculus (or the gizzard) which grinds up the food.  From there, the food goes into the intestines where enzymes dissolve the food into separate components for absorption into the blood stream.

In a bird that has PDD, the nerves at the base of the proventriculus are attacked by a virus causing it to swell and become paralyzed.  While the bird may maintain a healthy appetite, the parrot is unable to properly digest its food and support its nutritional needs. This is why it is called a “wasting” disease.  The undigested food in the digestive tract gathers bacteria.  In cases of severe dilation, the proventriculus can burst and food will spill into the abdominal cavity causing serious infection and often death.

Some of the clinical signs suggesting PDD are weight loss, lethargy, regurgitation, the passing of undigested food in the droppings and sometimes seizures.  A bird with PDD may have all or just some of these symptoms making a clinical (symptomatic) diagnosis very difficult.  Once the symptoms have manifested in a bird that does have PDD, the bird will typically die with in several months to a year.  It is a fatal disease – there is no known cure.

Unfortunately, it is unknown at this time how this disease is transmitted.  It is known to be contagious, however, and complete isolation of the diseased parrot is required.  Stringent measures need to be taken following contact with a bird known, or suspected, to have PDD before you handle any other birds, including a change of clothing and thorough disinfecting.  No healthy bird must come in contact with anything that has been in the presence of a bird with PDD.

Up until very recently, the only method of diagnosing PDD was a biopsy of the crop, proventriculus or the ventriculus. This is a very invasive, and expensive, procedure.  For years, the avian community has been very excited about  a diagnostic blood test being developed at Texas A&M’s Schubot Exotic Bird Health Center.  A couple of years ago, they were able to isolate a brain enzyme present in birds known to have PDD.  Not too long ago, this blood test was made available.  As far as I know, there is only one lab that is handling the new PDD testing, but it appears that the results, which take 3-4 weeks to come back, may be unreliable at this point.

A parrot known to have been exposed to PDD might test negative.  False negatives results occur frequently in testing of any kind.  While not all exposed birds contract the disease, you are aware of the exposure, and know that at some point testing may come back positive and can respond accordingly.  With a false positive, where the tests conclude that the disease IS present, a bird might be euthanized.  One bird that I read about tested positive, then later tested negative.  This is a concern.

PDD has been a worrying disease for a long time.  With so little understanding of the agent that carries it from one bird to another, it is very important not to bring your bird around other flocks.  When you have come in contact with birds other than your own, wash your hands, change your clothes.  Never share your birds toys with any other birds.  I don’t buy toys from bird fairs that cannot be sterilized at home.  There are a lot of birds passed around at these and other birds related events.  It was strictly against policy to bring your bird to any meeting at my former bird club in Austin for this reason.

When purchasing a new parrot, be sure to keep him quarantined for at least 4-6 weeks. During the quarantine period, it is assumed that any disease will present itself in the form of symptoms.  Although this is not always the case, it is a very good practice. Even a reputable breeder may not be aware of disease in his aviaries. Pet stores sometimes purchase their birds from bird mill type breeders because they get lower prices from them.  Bird mills are horrible places, and often disease ridden.

I was reading a heart breaking account on one of the bird forums the other day that prompted me to write this article.  One of the members on this particular board purchased a cockatoo from a pet store.  It became ill following its quarantine period and all of the clinical signs point to PDD.  Not only have the rest of her flock been exposed to the new bird and have had to be tested, but everything the new bird may have come in contact with that cant be sterilized, had to be thrown away.

For those of you with multiple birds, consider this:  everything made of rope, wood, or fiber must go.  Any food not sealed in zip lock bags must go.  All cages, toys and parts, including the quick links,  made of acrylic or metal must be taken apart washed thoroughly with bleach and water.  The infected bird must be isolated and put on a separate air system, which is not even possible in some households.  You cannot travel freely between this bird and your flock as showering, disinfecting and clothing change are imperative.  This is a daunting responsibility and a great deal of hard work and financial loss.

We all want to show off our birds and share playtime with our friend’s new bird, but this is how disease is passed on from one flock to another.  Since we don’t always know from appearance that a parrot is sick, think carefully before taking this risk.


At the recent Houston Parrot Festival, Dr. Sharman Hoppes from Texas A&M shared with the public more information on testing and dealing with the virus.  Recent updates include:

  • PDD in the environment:  While PDD does permeate the environment and is highly contagious, UV light kills it.  This means that to eliminate the disease in the environment, NOT the bird, we will roll our cages and toys out into the sunlight. This an amazing finding, proving once again that there is nothing quite as healing as sunshine!
  • Testing accuracy: Crop biopsies had been our chance to properly diagnose this disease, but are only 65% accurate.  Serological testing (blood serum) now has a 90% accuracy rate.  Fecal tests are also proving to be of value.  In a small study, the testing of a fecal sample three weeks in a row came back with accurate results.  The tests were done on droppings, meaning a vent swab is not necessary.  There is a need for further study before this is considered a reliable means of testing, but it looks promising.
  • Collecting specimens for testing: A very small study has shown that a fecal sample is best kept refrigerated, or in saline.

This is a huge advancement in a disease we know little about.  I’ll continue with updates as information becomes available.

Author Patty Jourgensen specializes in avian health, behavior and nutrition and has been working with and caring for rescue birds since 1987.

1 comment

Rhonda Reed

I acquired a baby african grey 8 weeks old which wasn’t weaned. I read up on how to look after this baby and did everything according to the book. It grew into a beautiful big strong bird. Then one day I noticed it looked like it was drooling saliva. I asked my vet what was the cause of this and the person who sold me the bird ( I have 10 other birds from the same breeder ) . No one could tell me why this bird was bending over and spewing saliva. Shortly after that she didn’t seem too well, her faeces had the most offensive smell. I took her to the vet they gave her an antibiotic injection. Five months down the line I ended up with a bird whose neck took the shape of a huge S. She continiously threw her head back fell off her purch had convulsions and was unsteady on her legs most of the time. After numerous visits to the vet and blood/faece samples and antibiotics no one had an answer. One day we found her almost dead after returning from work. We had her euthanised. I have had healthy parrots for over 5 years and this was the most heart breaking experience. Today after reading about so many diseases I believe she had PDD. She shared a cage for awhile with another parrot who is over 10 years old, till she started falling off the perch then we moved her to a small cage. He and the other parrots have had no symptoms.

Rhonda Reed

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