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Guidestar


Frequently Asked Questions (Printer-Friendly Version), (PDF)

reviewed by: Matthew S. Johnston, VMD, DABVP (AHN Advisory Board)


1. What is PDD?

2. What causes PDD?

3. Is there a cure?

4. How can I protect my bird?

5. What are some of the signs and symptoms of PDD?

6. How is PDD diagnosed?

7. Can my bird live with PDD?

8. How long does an infected bird live?

9. The hard questions.. what are my options?


1. What is PDD?


Proventricular Dilatation Disease (PDD) is used to describe an inflammatory response characterized by the accumulation of lymphocytes and plasma cells in the nervous system, especially the nerves that supply the muscles in the proventriculus and other digestive organs including crop, ventriculus and small intestine.

Proventricular Dilatation Disease (PDD) is a wasting type disease that can affect and is fatal in captive and free-ranging birds; especially young birds like African Greys; Macaws and Cockatoos.

The symptoms and side effects that have been associated with PPD are varied, its routes are unknown, and its outcome is fatal.

Research is currently underway to confirm the infectious nature of PDD, and determine one or more causative agents that progressively destroy the nerve supply to the bird's forestomach (proventriculus), the digestive chamber located in front of the gizzard (ventriculus). Slow starvation results from destructive, inflammatory changes in the brain and neural system affecting the gastrointestinal tract. The symptom that characterized PDD's original name, "Macaw wasting disease", was first found in macaws and refers to the body's tendency to consume its own fat resources for nutrition. When food is not processed and digested properly, undigested food accumulates, along with digestive tract bacteria, increasing the chances of infection. The forestomach becomes distended, its walls weaken, and compression of other organs or rupture can occur.


"I would like to mention that proventricular dilatation disease (PDD) is definitely on the increase, both in aviaries and in baby birds".- Margaret A. Wissman, DVM, ABVP - The Five Most Common Aviary Diseases, Bird Breeder Online, February 1998


Information on the Web
Proventricular Dilatation Disease, East Petaluma Animal Hospital

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2. What causes PDD?


  • How do birds get PDD, and how did my bird get PDD?
  • How is PDD transmitted, and how does PDD spread?
  • What is the likelihood my bird will get PDD or not get PDD?

Researchers are trying to confirm the infectious nature of PDD meaning that it can be transmitted between birds. If a bird is exposed to a PDD bird, the evidence suggests there is a possibility that it will host the disease as well. The cause of PDD is not known.

Various studies are being done such as the ones at the University of Georgia's College of Veterinary Medicine and Canada's University of Guelph, Veterinary Teaching Hospital to determine a cause of PDD. If a cause can be determined (viral, bacterial, parasitic, protozoal, prional), veterinarians and researchers may be able to establish proven treatment protocols.

An infection is defined as the invasion and multiplication of an infectious agent in or on a host; this infection may or may not cause disease....  An infectious disease is simply a disease caused by an infection and may be described as a viral, bacterial, mycotic, or parasitic according to the type of etiologic agent responsible. Most viral, bacterial, and mycotic diseases are infectious diseases in which the disease agent multiplies in or on the host.


- Katharine M. Kurkjian, University of Georgia College of Veterinary Medicine. Modes of Introduction of Exotic Animal Disease Agents


To evaluate the epizootiologic characteristics associated with naturally and experimentally induced disease, breeding pairs of cockatiels in which at least one individual of each pair was histologically positive for PDD were placed in a closed indoor room and provided nesting boxes. Most offspring were allowed to mature without interference while some were experimentally inoculated with tissue homogenates known to induce PDD. Adults and their offspring were monitored for clinical changes suggestive of PDD and birds that developed morbidity were euthanized and tissues were histologically evaluated. Results of this study confirm that some birds can be in direct contact with PDD positive birds for prolonged periods without developing disease, diseased adults can produce clinically normal offspring, chicks produced by positive parents are susceptible to disease, any immunity passed from a hen to her chicks is only transient and the period from exposure to the suspect PDD agent to development of overt clinical signs can be more than a year.


Branson W. Ritchie, DVM, PhD, Dipl ABVP and ECAMS;

Christopher R. Gregory, DVM, PhD; Kenneth S. Latimer, DVM, PhD, Dipl ACVP,
Denise Pesti, MS; Mary Ard, BS
Epizootiology of Proventricular Dilatation Disease in Breeding Cockatiels

Paper #290, AAV August 2004
 


Cause - The cause (etiology) of PDD is not known. The Emerging Diseases Research Group (EDRG) at the University of Georgia's College of Veterinary Medicine is trying to isolate a virus they believe may be causing the neural damage to the gastrointestinal system.

Modes of transmission - Scientists refer to the ways a disease spreads as "modes" or "routes" of transmission.


PDD's modes of transmission are not yet fully understood. The transmission of PDD may occur by either direct or indirect contact, or both.


Disease agents may be transferred by direct contact through physical contact, for instance, or by fecal to oral routes. Airborne transmission is also considered direct contact, and may be a possible route. The virus that causes Avian Influenza, for instance, is transmitted through the air when birds are in close contact. It has been observed that PDD is found more often in birds that share small spaces, do not have the advantage of being outside, or are stacked in cages in close proximity to one another. This anecdotal evidence is inconclusive and warrants further study.
Indirect contact via vectors is another way that disease agents like viruses may be able to move from one bird to another. A vector can be any intermediate agent that allows the transport and/or transmission of a pathogen. Lyme disease (where a tick is the intermediate agent) and West Nile virus (carried by mosquitoes) are examples of vector-borne diseases. (Fomites are inanimate objects that can carry infectious agents from one animal to another, such as clothing or food bowls with contaminated particles on them.)


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3. Is there a cure?

  • What kind of treatment is available for my bird(s)?
  • Is there a vaccination against the disease?

The innate characteristics of pathogenic organisms play a huge role in determining modes of disease transmission. Understanding these characteristics is essential to preventing disease introduction or controlling and/or eradicating them once introduced.


- Katharine M. Kurkjian, University of Georgia College of Veterinary Medicine

Modes of Introduction of Exotic Animal Disease Agents


The notion of a "cure" is a mistaken one. There are experimental treatments that are showing some promise but need further study. PDD often causes irreversible neural and gastrointestinal damage in afflicted birds. Science will never produce a cure that can restore a seriously diseased bird to its original state of health. Our companions, our flocks, are victims: that is why the disease is so devastating.

As research progresses and more has become known about the disease, ways are being developed to treat the conditions and side effects currently associated with PDD. Treatments may in some cases help afflicted birds to live longer and healthier lives, and may even help to prevent PDD from further damage to an individual bird. But without a deeper understanding of PDD's cause and modes of transmission and an accurate means of testing for PDD, treatment research will continue to have difficulty in assessing successes and failures. Responsible husbandry calls for continued isolation of a bird suspected of PDD until such tests have been developed.


Until such time when a particular agent that causes PDD is identified and a suitable diagnostic assay developed to identify infected individuals, the infectious status of treated/recovered individuals remains unknown.


- Bob Dahlhausen, Resolution of Clinical Proventricular Dilatation Disease

by Cycloogenase 2 Inhibition 


In addition to providing necessary information for research to help treat afflicted birds, this disease research naturally leads to effective means of protecting healthy birds and preventing outbreaks and the spread of infectious diseases. For instance, Psittacine Beak and Feather Disease (PBFD, now called circovirus), a highly infectious viral disease that ravaged our companions and flocks until recently, is effectively being controlled by the accurate testing and vaccine development which occurred as a result of the viral research.

It is beyond the scope of this FAQ to list or comment on medical treatment programs. Consult a veterinarian or veterinary hospital that has experience in identifying and treating avian diseases. See our PDD Research section for information about some of the research efforts currently under way in the United States.


  • Read what the bird folk have to say in our Living with PDD section.

    PDD is a disease of suspected viral etiology with a potentially long incubation period of months to possibly years. Because the lesions of PDD are inflammatory in nature, we speculated that diminishing this reaction might lead to clinical improvement and resolution of clinical signs in affected birds. Anti-inflammatory agents with significant activity in the CNS, peripheral nervous system, and gastrointestinal tract that were safe for use in pet birds were identified. Of these, the non-steroidal anti-inflammatory drugs (NSAIDs) appeared most useful...


    - Bob Dahlhausen, Resolution of Clinical Proventricular Dilatation Disease by Cycloogenase 2 Inhibition 


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    4. Is there anything I can do to prevent my bird from getting PDD?
    • How can I protect my bird(s), my flock(s) from PDD?

    Proventricular dilatation disease can occur in any aviary despite excellent hygiene, valid quarantine procedures and the absence of new additions to the flock. In some aviaries, numerous cases of PDD will occur simultaneously. In others, several affected birds may die, and the problem seemingly resolves, only to reappear 1 to 2 years later. In other cases, a single bird in a breeding pair may die, with no subsequent losses in the aviary even 4 to 5 years later. It is common for many birds exposed directly or indirectly to an affected bird to remain subclinical.


    Branson W. Ritchie, DVM, PhD, Dipl ABVP and ECAMS; Christopher R. Gregory, DVM, PhD; Kenneth S. Latimer, DVM, PhD, Dipl ACVP,

    Denise Pesti, MS;  Mary Ard, BS


    Epizootiology of Proventricular Dilatation Disease in Breeding Cockatiels, Paper #290, AAV August 2004


    Since it is not scientifically proven how PDD is transmitted, it is advised that broad control measures are instituted.

    Since no real conclusive results are yet available about PDD's transmission modes and its persistence in the environment, one is forced to take drastic measures to protect our birds from pathogens transmitted along any route. We can control what comes in to our facilities, and what goes out. Some of our homes and aviaries have begun to resemble sterile research laboratories.

    To avoid infection by direct contact, a bird presenting signs of PDD is isolated from other birds. Since airborne transmission has not been ruled out, this implies a separate airspace.

    Follow the rules of quarantine, changing potentially contaminated clothing (even our shoes!) and sterilizing objects in the avian environment. If hand feeding never share or reuse syringes and this includes water and food dishes, keep them marked for use in the same cages.

    Avoid known carriers, if possible, so that you do not infect healthy birds. Even so, there is no way to avoid exposure to unknown carriers.

    Quarantine all new additions. Keep all well check information current, this should include: CBC (blood chemistry), check for parasites, test for circovirus (PBFD), polyomavirus, and psittacosis.

    In birds showing symptoms discuss with your vet a workup to rule out other diseases that can cause similar symptoms, such as lead toxicosis, avian gastric yeast, mycobacteriosis, cancer, obstruction, etc.

    Since conclusive testing is under development, it is important to institute extraordinary monitoring measures.

    Regularly look for external signs of PDD. Keep a close eye on a bird's weight and appetite. Monitor undigested food in the droppings - and log your data to be reviewed with your treating veterinarian.

    If you feel there is an exposure take the precaution of obtaining CBCs and radiographs as baselines for discovering and monitoring internal signs of PDD.

    Information on the Web
    Characteristics of Infectious Disease Agents

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    5. What are some of the signs and symptoms of PDD?
    • Does my bird have PDD or is (s)he just clumsy?
    • My bird eats all the time - how could s(he) be sick?

    A bird carrying PDD may or may not show outward signs before the disease becomes critical. Dr. Hannis Stoddard cites reports of incubation lasting as long as eight years before clinical signs are exhibited, but some cases of acute outbreaks suggest that a shorter incubation period may be at play.

    The fact that some exposed birds remain normal is good news for the avicultural community. This suggests that continued research efforts could provide effective control measures to prevent disease. -
    Proventricular Dilatation Disease

    There are several common signs of PDD in a bird. Your veterinarian will be looking for signs of weight loss despite normal or excessive appetite, the passage of undigested food, vomiting, feather loss, abdominal distention, and impaction of the crop. The doctor will also look for neurological signs such as erratic and unusual head movements, spasms and seizures, lack of balance/excessive falling, and unusual apathy or sleepiness.

    Note that clinical signs like these may also indicate other diseases or conditions than PDD, and that some infected birds show no outward signs whatsoever.

    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 food in the feces indicating a malabsorptive or maldigestive disorder.- Dr Branson W. Ritchie, 2000 AAV presentation

    Proventricular impaction, muscle atrophy, abdominal enlargement, lethargy, weakness, polyuria, diarrhea, scant feces or hypotension have also been reported in some birds.  When the central nervous system is involved, signs may include ataxia (bird may fall from the perch), abnormal head movements or seizures. Some affected birds may develop central nervous system signs in the absence of gastrointestinal abnormalities.

    Proventricular Dilatation Disease: A Viral Epornitic - Reprinted in part from Avian Viruses: Function and Control by Psittacine Disease Research Group, University of Georgia, College of Veterinary Medicine in Athens, GA

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    6. How is PDD diagnosed?
    • Why can't my vet tell me if my bird has PDD or not?
    • Are there any tests available to detect PDD?
    • How accurate are they?

    A presumptive diagnosis of PDD is based on historical information, clinical signs, and radiographic evidence of proventricular dilatation or dysfunction. Confirming that a living bird has PDD is difficult. Biopsy of the ventriculus or proventriculus can be used to diagnose the disease. However, obtaining a biopsy sample from these organs is invasive and dangerous. In some birds, biopsy of the crop can be used to diagnose the disease. - Dr Branson W. Ritchie, 2000 AAV presentation

    Veterinarians often rely on the evidence of symptoms to establish a suspicion of the presence of PDD, rather than its diagnosis. They may recommend testing that will help confirm clinical signs, but existing tests may not produce conclusive results.
    The only definitive test that is available on a living bird is a biopsy of the gastrointestinal tract usually via the crop. If tissue is taken from the crop of an infected bird, and the tissue collected has PDD lesions present, it is possible to obtain a positive diagnosis accurately -- if the test result is positive, the bird is infected. If the test results are negative, the bird may or may not be infected because the sample taken may have been disease-free, meaning that the tissue sample did not include infected tissue present in the gastrointestinal tract at the time of biopsy. On a negative test you may want to discuss with your veterinarian protocols for follow up testing as it relates to your birds case.

    Another testing procedure uses a barium X-ray process to reveal advanced signs of PDD in a bird with gastrointestinal damage. This test does not establish the presence of PDD if existing damage is neurological. The inability to accurately diagnose PDD in our birds and flocks is a tragic aspect of this disease.

    Information on the Web:
    Avian Endoscopy, from ExoticPetVet.Net - Margaret A. Wissman, DVM, ABVP

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    7. Can my bird live with PDD?

    Your bird may be able to live with PDD. Some birds living with this disease present as such healthy birds that you would not know they are infected. Once symptoms appear, however, you can expect a deteriorating quality of life. As in so many terminal diseases, your goal is to provide the bird with the best quality of life within your means.

    Expect to use the same kind of care for a PDD-infected bird as for any organism whose immune system and other physiological systems are being compromised. Special attention to nutrition, hygiene, and isolation factors will help protect your bird from infections and other diseases.

    Despite the fact that testing for PDD remains in the experimental stages, and no one definitive test or treatment currently exists, there are steps you can take to avoid the spread of this disease throughout your aviary.

    - Husbandry, notes from Dr. Michael Taylor, University of Guelph, Ontario, Canada

    You may want to consult with avian behavioral experts about how to help improve the quality of life for a PDD-afflicted bird. Refer to our section on Living with PDD for stories of survivors, shared tips, and articles intended to help provide a better life for your exposed or infected bird.

    As you know, PDD can strike one or several birds in a home or aviary, and leave the others healthy. Why do some die and others never contract the illness? I believe that a partial answer lies in the functioning of the immune system. Genetically, some birds have weaker immune systems than others and there's not much we can do to change that. But we can certainly take the measures that will insure that the immune system of every bird we have is functioning optimally.


    Treatment programs are considered to be experimental until more research data about causes and the manner of transmission becomes available. Researchers are testing hypotheses that a given medication or process will help your bird live a longer and healthier life. Veterinarians rely on personal and collective experience to recognize and treat PDD symptoms as the research moves along.

    If you do have a PDD exposure in your home or aviary it is important to discuss with your veterinarian what standards should be used to help guard against exposing other birds before you bring in new or remove a bird from your flock. Until more is known about PDD this can not be stressed enough as this is our only known means to help control the spread of PDD at this time.

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    8. What is the lifespan of a PDD bird?


    Not enough is known about PDD to answer this question. The life span of a compromised bird depends on a wide range of variables, some of which are currently under study. It appears at this time that some birds live while carrying the disease - they are carriers that do not become symptomatic. While other birds lives may be reduced to a matter of months after exposure to PDD. It also appears that some PDD-infected birds may be able to produce PDD-infected offspring and/or have a high rate of dead in the shell.

    Provided with an easily digested high energy diet, a stress-free environment and treatment for secondary bacterial or fungal infections, affected companion birds can survive for months or years. Any bird with the disease that is being treated should be placed in strict isolation with no direct or indirect contact with other birds. Some birds with clinical changes suggestive of PDD have been reported to recover when provided supportive care. However, a positive diagnosis of this disease requires the demonstration of microscopic lesions in the nerves and none of the reported recoveries have been in birds confirmed to have PDD.

    Branson W. Ritchie, DVM, PhD, Dipl ABVP and ECAMS; Christopher R. Gregory, DVM, PhD; Kenneth S. Latimer, DVM, PhD, Dipl ACVP,

    Denise Pesti, MS;  Mary Ard, BS


    Epizootiology of Proventricular Dilatation Disease in Breeding Cockatiels
    Paper #290, AAV August 2004


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    9. The hard questions...


    • What are my options if I find out or suspect my bird has PDD?
    • Do I have to euthanize my bird/flock if I suspect PDD?

    We've heard these questions too often to leave them out... but, we do NOT have answers.

    • The first step, of course, is to quarantine the bird and consult a veterinarian or research hospital with experience in identifying and treating avian diseases. But don't be dismayed by a bad prognosis - while the research is incomplete, we can be as broad in our hopes as we are in our protection measures.

    • Educate yourself about the disease. See our PDD Research section for information about some of the research efforts currently under way in the United States and abroad.

    • Read what the bird folk have to say in our Living with PDD section.

    • Read more about treatment, above

    • Follow our links to the published literature, network with the avian community; join our Avian Health Network "Living with PDD" email group for support.

    • Try to gather all the information available and review it with your trusted avian medical professional.

    • Then try to figure out what is best for your bird(s) and for you. No one can make these decisions for you. Your decisions will be based on a wide range of variables from your ethical and religious beliefs to practical factors such as expense, risk factors, and exposure to other birds.

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      (Please send all comments, questions, and suggestions for additional resources to the AHN Board of Directors.)

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