Proventricular dilatation disease (PDD) — also known as macaw wasting disease or neuropathic gastric dilatation — is a serious and often fatal neurological disease of psittacine birds (parrots). PDD is caused by avian bornavirus (ABV), which triggers an immune-mediated inflammatory response that destroys the nerves supplying the gastrointestinal tract (most commonly), the brain, and other organs. The disease causes the proventriculus (glandular stomach) to lose its ability to contract and process food, leading to progressive weight loss and wasting despite a maintained appetite. PDD remains one of the most challenging diseases in avian medicine, with no cure currently available.
Overview
Avian bornavirus (ABV) is an RNA virus that infects the nervous system of psittacine birds. However, infection with ABV does not always lead to PDD — many birds carry ABV without developing clinical disease. PDD develops when the immune system mounts an inflammatory response against ABV-infected nerve ganglia, particularly those of the gastrointestinal tract (myenteric and submucosal plexuses). This inflammatory destruction of the nervous system leads to loss of GI motility and function.
PDD has been documented in a wide range of psittacine species, with macaws, African Grey parrots, Amazon parrots, cockatoos, and conures being most commonly affected. The disease can also affect non-psittacine species including canaries and waterfowl.
Transmission is believed to occur through fecal-oral and urofecal routes, possibly also through feather dust and crop secretions. The incubation period is variable and may be weeks to years.
Symptoms
PDD primarily affects the GI tract, but neurological signs can occur independently or alongside GI signs:
Gastrointestinal signs (most common):
- Progressive weight loss despite a good or even increased appetite (the hallmark of PDD)
- Regurgitation
- Passage of undigested or partially digested food in the droppings (whole seeds visible in feces)
- Crop stasis (crop fails to empty normally)
- Abdominal distension
- Vomiting
Neurological signs:
- Ataxia (uncoordinated movement)
- Seizures
- Head tremors or tilting
- Blindness
- Leg weakness or paralysis
- Behavioral changes
Some birds develop neurological signs without GI involvement, and vice versa. The disease is progressive and ultimately fatal in most clinically affected birds, though the rate of progression varies widely.
Diagnosis
Definitive diagnosis of PDD is challenging:
- ABV testing (PCR) — Choanal and cloacal swabs or blood samples tested by PCR for avian bornavirus RNA. A positive result confirms ABV infection but does not confirm PDD (many carriers are asymptomatic). A negative result does not rule out PDD due to intermittent shedding.
- ABV serology (antibody testing) — Detects antibodies against ABV. Similar limitations to PCR regarding the distinction between infection and disease.
- Radiographs — May reveal a dilated (enlarged) proventriculus, sometimes visible as a greatly distended organ occupying much of the coelom. Barium contrast studies show delayed GI transit and proventricular retention.
- Crop biopsy — The most reliable antemortem diagnostic test. A surgical biopsy of the crop wall examined histopathologically for lymphoplasmacytic ganglioneuritis (inflammation of the nerve ganglia). A positive biopsy is diagnostic, but a negative biopsy does not rule out PDD as inflammation may be patchy.
- Blood work — May show malabsorption-related changes but is non-specific.
- Post-mortem histopathology — Definitive diagnosis is often made at necropsy, revealing characteristic lymphoplasmacytic ganglioneuritis throughout the GI tract and/or CNS.
Treatment & Medications
There is no cure for PDD. Treatment is supportive and aimed at modulating the inflammatory response:
| Medication | Purpose | Key Notes |
|---|---|---|
| Celecoxib | COX-2 selective NSAID | The most commonly used medication for PDD. Reduces the inflammatory damage to nerve ganglia. Some birds show significant clinical improvement and prolonged survival. Dose: 10-20 mg/kg orally twice daily (species-dependent). |
| Meloxicam | NSAID | Alternative anti-inflammatory. Less commonly used than celecoxib for PDD. |
| Metoclopramide | Prokinetic | Stimulates GI motility; may help with crop stasis and GI transit. |
Supportive Care
- Dietary modification — Easily digestible, soft foods. Soaked pellets, cooked grains, and formulated hand-feeding diets help compensate for impaired digestion. Avoid whole seeds that the bird cannot break down.
- Nutritional support — Supplementation and caloric support to combat wasting.
- Crop feeding — May be necessary for birds with severe crop stasis or those unable to maintain adequate nutrition.
- Stress reduction — A calm, warm environment with minimal handling.
Prognosis
- PDD is generally considered a progressive, ultimately fatal disease.
- Some birds treated with celecoxib show significant clinical improvement and can survive for months to years with ongoing treatment and supportive care.
- Birds with predominantly neurological signs generally have a poorer prognosis than those with GI-only disease.
- ABV-positive birds without clinical signs may never develop PDD, or may develop disease months to years after initial infection.
- Spontaneous remission has been rarely reported.
Frequently Asked Questions
Is PDD contagious to my other birds? ABV (the virus causing PDD) is contagious between birds, primarily through fecal material. However, ABV infection does not always lead to PDD. The decision about how to manage multi-bird households with an ABV-positive bird is complex and should be discussed with your avian veterinarian.
Should I test all my birds for ABV? If one bird in a flock is diagnosed with PDD or tests ABV-positive, testing other birds may be advisable to understand the flock’s ABV status. However, management decisions are not straightforward — ABV-positive asymptomatic carriers may never develop disease. Your avian veterinarian can help you interpret results and make decisions.
Can PDD be prevented? There is currently no vaccine for ABV. Prevention relies on screening new birds before introduction to a flock, quarantine protocols, and good hygiene. However, given that ABV carriers may test negative intermittently, screening is not foolproof.
Will my bird suffer? PDD can cause significant weight loss and discomfort. Quality-of-life discussions with your avian veterinarian are an important part of managing this disease. Palliative treatment with anti-inflammatories and supportive care can maintain comfort, but humane euthanasia should be considered when quality of life declines despite treatment.
Is PDD the same as “going light”? “Going light” is an older term used in aviculture for any bird that loses weight progressively. PDD is one specific cause of going light, but weight loss in birds can result from many conditions including infections, parasites, organ disease, and malnutrition.