Proventricular Dilatation Syndrome (PDS) , also known as Macaw Wasting Disease or Macaw Fading Syndrome (it was first seen in macaws), and Neuropathic Wasting Disease is a devastating disease of mostly young psittacines.

Macaw with a metal bell stuck on its tongue

This playful Macaw with a bell stuck on its tongue shows how interesting these birds are. Thankfully, we do not see many Macaws with PDS at LBAH anymore. Click here if you want to see how we removed the bell from this tongue. 




It occurs in over 50 species of parrots. Common species are African Grey parrots, Amazons Macaws, and Cockatoos. It is suspected to also occur in non-psittacine birds like canaries, weaver birds, and toucans.

The proventriculus is the chamber of the digestive tract just in front of the ventriculus (gizzard). When it dilates there is an inability of the stomach to digest food. It can be a problem in any psittacine, but is found most commonly in macaws and cockatoos.

Cause

A virus called a bornavirus is the suspected cause. This virus is shed in the feces, saliva, and respiratory secretions intermittently.

Symptoms

Birds that have this problem are weak, have lost weight, and can have difficulty perching. Many of them will have impacted crops, regurgitate and pass undigested seeds in their droppings. Some will show neurologic signs like tremors, inability to perch, seizures, and paralysis.

Prominent keel on Macaw that has lost weight

It was originally called “wasting disease” because these birds would lose weight and we could palpate the prominent keel bone from the breast muscles wasting away. The proper term is atrophy of the muscles. Notice the IV catheter in this bird for fluid administration

These are also the symptoms of lead toxicity in some birds, so they are not specific for PDS. The term for a disease that is specific for a set of symptoms is pathognomonic. This is a rarity in veterinary medicine.

Since these birds can no longer digest and absorb food they lose weight and their keels become very prominent. This is why it was originally called Macaw Wasting Disease.

Regurgitation of a mucous like fluid is one of the classic signs of PDS. There might be seeds adhered to the mouth and feathers around the face.

Diagnosis

Macaw undergoing an exam by one of our doctors

Every diagnosis starts with a thorough exam. 

Young cockatoos and macaws that have symptoms of this disease warrant further diagnostic tests. Other diseases can mimic PDS, so it is important to follow a thorough diagnostic process. Baby birds and those with infections, cancer or toxicities can also have a dilated proventriculus.

This virus can be checked for by submitting special fecal or cloacal samples, in addition to blood samples looking for antibodies to the virus. These tests are called the Western Blot test or an ELISA (enzyme linked immunosorbant assay) test. A PCR test is also used. False negatives and false positives occur to these tests, so they are not reliable for a definitive diagnosis.

A biopsy of the crop or proventriculus is needed to confirm the diagnosis. The pathologist is looking for what is called a lymphoplasmacytic infiltration in the nervous tissue.

X-rays are a significant aid in making this diagnosis. The chambers of the stomach will show enlargement, which can be outlined with barium. Barium allows us to see the structures of the digestive tract more clearly. It also lets us know if the digestive tract is normal by assessing how long it takes for the barium to pass through to the end.

To understand how we perform a radiographic analysis of this problem it is important to understand the radiographic anatomy of a bird.

This is a normal x-ray of a bird laying on its right side. The head is towards the left. The diagram below explains the structures.

AS- air sac
PV- proventriculus
Vent- ventriculus (gizzard)
S- spleen
H- heart

Normal bird xray lateral view

Do you see the proventriculus on this digital radiograph that shows tremendous detail?

normal bird xray with the proventriculus circled in red

The proventriculus is circled in red

This bird has PDS. The arrows circle the hugely dilated proventriculus.

We frequently give barium to help in outlining the digestive tract and to look for causes of the dilated proventriculus other than PDS.

In this x-ray the barium filled crop is on the far left (arrow on far left), there is barium in the esophagus (arrow in middle) and the ventriculus has barium in it (arrow on far right). The dilated proventriculus, without any barium in it, can be seen just to the left of the ventriculus.

Treatment

PDS carries a poor prognosis. Medication to minimize vomiting and supportive care with fluids, antibiotics, and feeding small amounts of food at each meal might be helpful temporarily. Some birds have responded to higher doses of anti-inflammatory drugs like cortisone. It does not cure the problem, and if it works it tends to be temporary.

Birds with this problem need to be isolated from other birds.

If your bird suddenly becomes ill The Long Beach Animal Hospital staffed with emergency vets is available until the evenings 7 days per week to help if you see this in your pet, so please do not wait or attempt to take care of this problem on your own. If you have an emergency always call us first(562-434-9966) before coming in so that our veterinarians can advise you on what to do at home and so that we can prepare. To learn more please read our Emergency Services page.

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