Avian Bornavirus (Proventricular Dilatation Disease) in Macaws

Avian bornavirus is a virus associated with proventricular dilatation disease (PDD), a serious inflammatory nerve disorder seen in parrots, including macaws. You may also hear it called macaw wasting disease. In affected birds, the nerves that control the digestive tract can become inflamed, so food does not move normally. Some birds also develop neurologic signs because the disease can affect the brain and spinal cord.

The classic digestive change is an enlarged proventriculus, which is the glandular stomach. When that part of the digestive tract loses normal nerve function, a macaw may keep eating but still lose weight, regurgitate, or pass undigested food in the droppings. Not every bird shows the same pattern, though. Some have mostly digestive signs, while others show tremors, weakness, poor coordination, or behavior changes.

This condition is considered very serious. Once a macaw is showing clear clinical signs, the disease is often progressive and can be fatal. That said, the course is variable. Some birds decline quickly, while others have a slower course and may benefit from supportive treatment plans tailored by your vet.

PDD is linked to avian bornavirus, especially parrot bornavirus strains found in psittacine birds. The virus is considered neurotropic, meaning it targets nervous tissue. In macaws, that can lead to inflammation of the nerves that control the crop, proventriculus, intestines, and sometimes the central nervous system.

Researchers know the virus is strongly associated with the disease, but not every bird that tests positive becomes sick right away. Some birds may carry or shed the virus without obvious signs for a period of time. That is one reason diagnosis and flock management can be challenging.

Spread is thought to occur through exposure to infected feces, urine, feather dust, or contaminated environments, and close contact between birds likely increases risk. Stress, crowding, and introducing new birds without quarantine may make spread more likely. Your vet can help you interpret risk if you have a multi-bird household or aviary.

Diagnosis usually starts with a careful history and physical exam. Your vet will want to know about weight trends, appetite, droppings, regurgitation, activity level, and any neurologic changes. Because many bird illnesses can look similar, your vet may also recommend baseline bloodwork and fecal testing to look for dehydration, infection, inflammation, or other causes of weight loss and digestive trouble.

Imaging is often an important next step. Radiographs may show an enlarged proventriculus, and some avian veterinarians use a contrast study to see how food moves through the digestive tract. These tests do not prove PDD by themselves, but they can strongly support the diagnosis when paired with the right clinical signs.

Testing for avian bornavirus may include PCR on cloacal swabs, choanal swabs, or feces, and sometimes blood-based testing. A positive result supports exposure or infection, but it does not always predict whether a bird has active clinical disease. In some cases, your vet may discuss biopsy or, after death, necropsy with histopathology, which remains one of the strongest ways to confirm the characteristic nerve inflammation.

Prevention focuses on biosecurity and careful bird introductions. If you bring home a new macaw or other parrot, keep that bird separated from resident birds during a quarantine period recommended by your vet. During that time, avoid shared food bowls, perches, cleaning tools, and direct contact. Good handwashing and changing clothes after handling different birds can also help reduce spread.

Because avian bornavirus may be shed in droppings and urine, routine cleaning matters. Remove waste promptly, disinfect cages and surfaces regularly, and keep food and water dishes clean. Reducing crowding and stress may also help support overall health in multi-bird homes.

There is no widely used routine vaccine for pet macaws for this disease. Screening new birds with an avian veterinarian may be helpful, but testing has limits because some infected birds shed intermittently and some positive birds are not yet clinically ill. The most practical prevention plan is a combination of quarantine, sanitation, careful monitoring, and early veterinary evaluation for any bird with weight loss, regurgitation, or neurologic changes.