Psittacine Proventricular Dilatation Disease
Dr. Christopher R. Gregory
Psittacine proventricular dilatation disease (PDD) is the term used to describe a disease in companion birds that prevents them from properly digesting food. The problems with digestion are caused by inflammation of nerves in the gastrointestinal (GI) tract. The inflammatory cells, lymphocytes and plasma cells, invade the GI neural tissues, resulting in decreased to absent food movement (GI motility) and absorption. The presence of whole seeds in the feces (birds on a seed-based diet)
Many diseases will cause similar GI and neural problems. These include
anything that obstructs or prevents the normal functioning of the GI tract, such as parasites, tumors, foreign bodies, fungal or bacterial infections, and heavy metal poisoning. Similar neural signs can be caused by systemic diseases such as liver or kidney failure, bacterial and viral infections, and heavy metal poisoning.
The disease was first reported in the late 1970s in imported macaws, hence the original term, "macaw wasting disease." To date, PDD has been observed in all species of psittacine birds and perhaps in non-psittacine species as well.
A virus is suspected to be the cause of PDD. The inflammatory cells (lymphocytes and plasma cells) are common in viral infections. Other studies and clinical data suggest that the disease is transmissible.
What To Watch For
A microscope is necessary to diagnose PDD. However, PDD should be considered when the following clinical signs are noticed:
Depression or lethargy
Regurgitation or vomiting
Weight loss (often seen as a prominent keel or breastbone)
Signs of nervous system damage (neural signs). These signs occur because lymphocytes and plasma cells invade the brain and spinal cord. Common signs of the neural form of PDD are head shaking, seizures and inability to stand or maintain balance.
A complete workup is necessary to diagnose PDD and exclude other diseases. Your veterinarian should recommend tests that may help in diagnosing PDD.
A complete medical history and physical examination of the bird and information about the bird's home environment will aid in diagnosis.
A complete blood count, urinalysis and serum biochemistries will help in detection of non-PDD disease.
Radiographs, with or without contrast studies, will aid in detecting dilatation and abnormal movement of the GI tract as well as any obstructions in the GI tract. Radiographs (X-rays) of the proventriculus (the organ just above the ventriculus or gizzard) or contrast (barium) studies may show dilatation of the organ.
Bacterial or fungal cultures and sensitivities may be recommended to identify and treat secondary bacterial or fungal infections often seen in PDD.
Ultrasound and fluorometry will also detect dilatation and abnormal GI function.
If the bird has died, your veterinarian may suggest a necropsy (autopsy of an animal) to look for causes. Many birds with PDD will show pectoral (breast) muscle loss and dilatation of one or more GI organs, particularly the proventriculus.
Biopsy. PDD may be suspected with any of the above-mentioned findings, but it can only be diagnosed with a microscope. Your veterinarian may recommend a tissue (crop, proventriculus, ventriculus) biopsy to diagnose PDD. Or, if the bird was necropsied, a complete set of GI tissues can be sent to a pathologist for evaluation. A pathologist will receive the tissue and, after some preparation, will look at the tissue with a microscope (histologic evaluation).
If lymphocytes and plasma cells are seen in the nerves of the GI tract, then a diagnosis of PDD is made. Common pathology terms for this condition are myenteric ganglioneuritis, lymphoplasmacytic ganglioneuritis or lymphoplasmacytic ganglionitis. All terms mean the same thing: PDD.
There is no specific treatment for PDD. Your veterinarian may recommend special diets that are more digestible. If secondary infections are present, your veterinarian may prescribe antibiotics or other treatments.
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 provided with supportive care 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.
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 re-appear one to two years later. In other cases, a single bird in a breeding pair may die, with no subsequent losses in the aviary even four to five years later. It is common for many birds exposed (directly or indirectly) to an affected bird to remain asymptomatic.
Mates, offspring or siblings of birds that are diagnosed microscopically with PDD should be considered at extra risk of developing the disease; however, they should not be euthanized. Many of the birds that are directly exposed to those with PDD never develop the disease. Until appropriate preventative measures can be developed, it would be prudent to place exposed birds in isolation.