Proventricular dilatation disease in parrots: the avian bornavirus finally identified
Proventricular dilatation disease, often shortened to PDD, remains one of the most feared diseases among owners of large parrots: a bird that loses weight despite a good appetite, regurgitates poorly digested seed, and sometimes declines neurologically within months, with no clear infectious agent identified for decades. A study by Amy Kistler, Amanda Gancz and colleagues, published in 2008 in Virology Journal, isolated a previously unknown virus, avian bornavirus, from parrots with PDD, proposing for the first time a credible causal agent for the disease (study on Google Scholar). That discovery changed how the disease is diagnosed and managed, in breeding facilities and family aviaries alike.
What is proventricular dilatation disease?
PDD affects the bird's digestive tract: the proventriculus, the glandular part of the stomach, gradually dilates and loses its ability to grind and move food along normally. The nerves that control gut motility are attacked by chronic inflammation, which explains both the digestive signs (regurgitation, whole seed in the droppings, weight loss) and the neurological signs sometimes seen alongside them, such as loss of balance or tremors.
The role of avian bornavirus
The virus identified by Kistler and colleagues doesn't explain every PDD case on its own: not every bird carrying it develops the disease, and individual factors (stress, immunity, genetics) appear to influence how it progresses. A blood test or cloacal swab can now screen a suspect bird for the virus, even before clear clinical signs appear, making early isolation easier when a new bird joins a group.
What signs should raise a flag?
Progressive weight loss despite a maintained appetite, visible, poorly digested seed in the droppings, repeated regurgitation outside a breeding context, or balance problems in a previously healthy parrot warrant a prompt visit to an avian vet. The signs your bird is sick help tell these symptoms apart from an ordinary digestive upset. By contrast, an abnormally overgrown beak usually points to a different cause, covered in our guide on an overgrown beak in birds, where beak and feather disease virus (PBFD) is discussed separately from bornavirus.
Frequently asked questions
Is PDD contagious between birds?
Avian bornavirus spreads mainly through droppings and secretions; strict quarantine of any new bird remains the best protection for an established aviary.
Is there a cure?
There is no cure for the virus itself, but anti-inflammatory treatment and tailored nutritional support can often slow progression and improve the bird's comfort.
Are all parrot species affected?
Large parrots (macaws, African greys, Amazons, cockatoos) are the best documented, but cases have been reported across many other psittacine species.
This guide is part of Planète Pets’s Birds universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.