Avian Bornavirus (ABV) aka Proventricular Dilatation Disease, (PDD), Macaw Wasting Disease
Ron Hines DVM PhD
What Is This Disease With Many Names?
In the early 1970s, changes in USDA regulations allowed a tremendous upsurge in the importation of wild parrots. Exportation of these birds in mass from tropical countries to developed countries soon followed and continued through 1993. Most of these birds were wild-caught adults with little potential as pets. Most were sold to breeding enthusiasts as foundation breeder pairs. I surgically sexed most that entered through the State of Texas at that time.
It soon became apparent that more than parrots were being exported. Among the Old World parrots and cockatoos, a mysterious loss of feathers and declining general health became common. By 1991, a team at the University of Georgia had identified an avian circovirus as the cause. (ref)
Among the New World parrot imports, particularly the macaws, a strange, progressive syndrome (disease) of depression, loss of body weight and inability to properly digest their food became apparent. Breeders and veterinarians labeled the disease Macaw Wasting Syndrome. No treatments helped these birds and no cause could be identified. It took until 2008 for the true cause of this syndrome to be identified. During that time span, the disease was given many names including : Macaw Fading Syndrome, Neuropathic Gastric Dilatation, Proventricular Dilatation Disease (PDD) and Myenteric Ganglioneuritis. It was eventually diagnosed in over fifty species of parrots other than macaws and the list continues to grow. It became apparent that Old World Parrots, like African Greys were also susceptible to the disease. PDD appears to be a more recently arrival in Australia. (ref)
Two distinct sets of symptoms occur in PDD. The best known are those related to destruction of the nerves responsible for normal movement of food through your bird’s digestive tract (destruction of its autonomic ganglia by the bird’s lymphocytes and plasma cells). The second set of symptoms relate to nerve tissue inflammation and destruction caused by the bird’s own immune cells (nonsuppurative inflammatory infiltrates) in its brain, spinal cord and, occasionally, its heart and adrenal glands. One or the other set of symptoms often predominate – but both can occur in the same bird. You can read a 1995 chapter that describes what veterinarians have traditionally known about PDD dynamics here.
In 2008/9 two research groups, working independently identified the virus that was the root cause of PDD. (ref1, ref2) It was a member of a small (there are only two known bornavirus) group of virus named after the German hamlet of Borna, where it was first described in 1885 when it caused the deaths of a group of cavalry horses. How Avian Bornavirus relates to this previously-known bornavirus is unclear. The one that affects horses can, apparently, affect many species of animals – from birds. (ref) to cats (ref) (A few have even suggested it might affect humans (ref) .
What Do We Know About The Avian Bornavirus?
Veterinarians suspected that a virus was the root cause of PDD from the get go. Now that the culprit virus has been found, the term PDD is gradually being replaced by ABV (Avian BornaVirus). Bornavirus have a natural affinity for nerve tissue. As such, they are called neurotropic virus. It is a very distant relative of the neurotropic viruses that cause rabies and polio. Between its discovery in 2008 and 2012, six or seven distinct genetic virus subtypes (= strains = genomes) of the Avian Bornavirus have been reported.
If My Parrot Has Proventricular Dilatation Syndrome/ABV What Signs Might I See?
Digestive Tract Signs
The first signs many owners notice is a lack of activity in their parrot, disinterest in its environment and a sleepy attitude. I think of them as having a generalized bedraggled look. When these parrots are handled, it is usually quite apparent that they have lost weight in their breast area. These parrots usually continue to eat – but as the disease progresses, owners often notice that their stools have changed. What was once a homogeneous greenish stool is now gritty with undigested food particles and seeds. These parrots often begin to regurgitate (vomit). In some, their crops become visibly enlarged.
These parrots may temporarily improve when given antibiotics. They have their good and their bad days or weeks but their long-term health remains in general decline.
None of these symptoms you see prove that your parrot has PDD/ABV – all could have other causes and the symptoms vary greatly between individual birds.
Bornavirus not only has the potential to attack the nerves in your parrot’s digestive system, it is quite likely to destroy nerves in other areas, particularly the bird’s brain and spinal cord. Signs of that destruction can appear suddenly or as a gradual decline. Parrots with his form of PDD may just appear weak, or they may loose their ability to stay on the perch, walk, or just appear clumsy. One leg or wing or both might be equally affected. Head tremors and shaking might occur and, occasionally, these birds suffer from personality changes or seizures. You can read more about the cause of these neurological symptoms here and here.
Although it is common for either the digestive or the more generalized neurological signs to predominate, it is not that unusual for both to be present to some extent in the same parrot. There are also a few veterinarians who believe that the neurological form of PDD/ABV might be involved in feather plucking, self-trauma and nephritis . (That has yet to be proven)
What Is Going On Inside My Parrot?
Bornavirus can set up a situation where the parrot’s own immune system destroys the ability of its nerves to function. Exactly why this occurs is not yet known. Some virus cause disease by actually destroying cells. But there are a few that cause the release of body chemicals that cause the pet’s own immune system to rush to the area causing a chronic inflammation that eventually destroys the body’s own tissue. The most common virus of that type that veterinarians struggle with is the coronavirus of cats responsible for feline infectious peritonitis (FIP). Avian bornavirus may well be another.
In the digestive tract form of avian bornavirus infection, the local nerve centers (myenteric plexuses) in the walls of your parrots digestive system that are responsible for normal motility (peristalsis) are slowly destroyed by a mixture of the parrot’s own immune cells (lymphocytes and plasma cells).
Without that normal wave action in the bird’s digestive tract, food backs up and is not properly digested or absorbed. The most common place for that to first occur is in the bird’s fore-stomach or proventriculus. Without the ability to properly digest food, food ingredients pass through the bird without much change in their composition. The blockages that occur also make the parrot susceptible to bacterial and fungal infections and overgrowth. Birds in this condition must fall back to living on their fat and muscle stores which is why their breast muscles shrink so profoundly. The parrot’s crop also relies on peristalsis to move food along. So crop impactions (blockages) are common as well.
When it is the birds central nervous system (CNS) where the majority of the inflammation is occurring, owners will see a wide variety of neurological (nerve-related) symptoms as the bird looses control of its body.
Bornavirus can also affect the nerves that keep the heart beating (Purkinje Fibers) leading to sudden death. Portions of its adrenal glands are modified nerve cells too. (ref) Their destruction can occasionally cause a parrot with ABV to die without prior warning.
Can Any Species Of Parrot Catch This Virus?
There are about 354 kinds of parrots. So far, avian bornavirus has been detected in over 50 of them. We know that bornavirus, in general, are not that particular about the species they live in. So there is no reason to believe that any species of parrot would not be susceptible to it.
How Do Parrots Become Exposed To This Virus?
How Infectious Is It ?
Not enough time has passed since the discovery of the virus for veterinarians to work that out with any certainty. The bornavirus is not very stable in the environment – so close contact between an infected and an uninfected bird is probably required. As with all infectious virus that are present in stool and oral secretions, the more parrots are confined to a relatively small area, the poorer the sanitation and the higher the stress level, the more spread of infection is likely to take place. Both the fecal and the urine portion of a parrots stool can contain the virus. (ref)
But the history of avian bornavirus in parrots tells us that much more than exposure to the virus is required for a bird to become physically ill. It is well known that many parrots kept in close contact with a known ABV/PDD bird never become ill.
Complicating our understanding of how this virus moves between birds is the fact that very long periods of time can pass (years) between the time the parrot is exposed to bornavirus and the time it becomes ill. That could easily explain why ABV/PDD can occur in a parrot whose nutrition and environment is now superb and why long periods can pass in an aviary with no new cases, only to have one appears years down the road.
So the mystery is more likely about how individual birds’ immune system reacts to infection than how infectious the virus itself is. That seems to be the case with the borna virus of mammals as well – lots of animals are exposed to the virus (about 60%) but only a few (5%) of those get ill.
Although most veterinarians believe that avian bornavirus probably moves from bird to bird through ingestion or inhalation of droppings or saliva of adjoining parrots that carry the virus, (ref) there is evidence that it might be transferred (vertically) from an infected female to its offspring thought through the egg as well. There are also veterinarians who believe that the strain of bornavirus that the bird encounters is important in determining how severe a disease will develop.
My Parrot Looks And Acts Fine. Does That Mean It Does Not Carry The PDD Virus ?
Parrots can carry the virus and look perfectly fine. Complicating the situation, antibody tests to detect prior exposure to the virus are not that accurate. And since it appears that the virus often “hides” in the body and only appears in the bird’s stool and secretions intermittently, negative result in tests that detect the virus itself can be inaccurate as well. You can read more about that situation here.
In 2010-2011, the PDD/ABV status of 63 parrots in three large European aviaries with prior PDD cases were studied for a one-year period. Of the 63 parrots, 43 were positive at least once during the year on a PCR test, antibody test or both. But of those 43 birds, only 6 developed PDD symptoms. Thirteen birds were positive on antibody test but not PCR tests and 8 parrots were positive on PCR tests but negative on antibody tests. Of the 63 birds, 23 remained negative on both tests throughout the year – even though the were kept in the same aviaries with infected parrots. The birds most likely to become sick appeared to be the ones with both a high antibody titer and a strongly positive PCR test (high virus load). You can read that study here.
How Will My Veterinarian Diagnose This Disease?
Until recently, veterinarians based their diagnosis on the symptoms they saw in your bird
after they ran a number of tests to eliminated health problems that might have similar symptoms (e.g. lead poisoning, digestive tract yeast infections, vitamin A deficiency, mycobacteriosis, cancer, gastric or intestinal obstructions, etc.)
Tracking the passage of barium radiologically (barium swallow) through your parrot’s digestive system was an accurate way of detecting the enlarged, slow-to-empty proventriculus common in many cases of PDD/ABV.
Diagnoses made in that way were usually correct – but they were only tentative (the “most likely” diagnoses). Absolute diagnosis relied on a veterinary pathologist identifying the telltale inflammatory changes on slides of the bird’s tissue. Although that could occasionally be done with biopsy specimens from the bird’s crop, almost all were made on tissues obtained after the bird had died. When the parrot only suffered from neurological symptoms, even the crop biopsy test was not an option.
Are There Tests To Determine If My Parrot Has Been Exposed or Carries The Bornavirus?
Yes, there are two. Both these tests currently have major limitations; but they are light years better than what we had a few years ago. It is always best if both tests are run – in some cases multiple times. You also need to keep in mind that it is not the end of the World if an otherwise-normal parrot is positive in either test. Combined results from many avian laboratories indicate that perhaps a quarter of domestic parrots in the United States have been exposed or carry the virus.
Bornavirus Antibody Test
The majority of parrots that are exposed to bornavirus produce antibodies against it . The test currently in use to detect these antibodies when they are present in the bird’s blood is called an ELISA test. The problem with this test is that it appears that not all infected birds produce detectable amounts of antibody, those that do, may only produce them intermittently and antibody can persist in the bird’s blood even after a parrot has successfully cleansed its body of the bornavirus.
In many disease situations, a high antibody titer protects against infection or symptoms. That does not appear to be the case with ABV. You can read a study about that here. So high antibody levels in your parrot do not appear to protect it from disease.
RT-PCR Tests To Detect The Actual Presence of Virus
We know that parrots infected with PDD/ABV have bornavirus widely distributed in their bodies. In infected parrots, these virus particles can often be detected when fiber swabs of their upper throat (choana) or cloaca or samples of their blood are examined using a highly sensitive testing method called a real-time reverse-transcriptase or rtPCR test . (ref) However, the virus often directs its activity toward nerve tissue, not the tissues that can be readily sampled. It has also become apparent that it is not always detectable even in known bornavirus infected birds. Some parrots shed the virus in their stool and secretions constantly, others only intermittently. That is not a unique problem in medicine; herpes virus another organism that dwells in nerves between flare-ups also gives false negative PCR tests. (ref) Alternative explanations could be that the nerve inflammation of PDD/ABV can continue even after a parrot has eliminated the bornavirus from its body or that one strain of ABV might be more serious (pathogenic) than another. ………we just do not know.
Some testing laboratories believe that looking for the virus trapped in a feather sample (calamus) from the bird is more likely to find the virus when it is present.
Remember that a positive PCR test does not mean that your parrot will ever become ill with PDD/ABV. The test is best used to confirm that a sick bird’s symptoms might be related to avian bornavirus or in the selection of breeding stock.
Combining the percentage of positive test results from many labs to date, I would guess that perhaps 1/4 of the larger domestic parrots currently carry the virus or were exposed to it. Their percentages of positive parrots are higher, but samples from ill birds are more likely to be submitted for analysis. A recent European study tends to confirm that. You can read it here.
Can Bornavirus Infections Be Treated Successfully – Is There A Cure?
There is no known cure for avian bornavirus infection. But some veterinarians claim successful treatments or, at the least, successful prolonging the bird’s life. The most promising treatment has been to suppress the parrot’s own inflammatory response. The most effective drug for that so far has been an NSAID called celecoxib (Celebrex®). You can read about that here. That article was written some time ago. Perhaps there are newer medications that perform better.
Many veterinarians and aviculturists believe that birds under stress are more likely to develop PDD/ABV symptoms than those that are not. That is the case in many diseases. All forms of wildlife tend to internalize chronic stress. When they do, their immune system often fails. So you veterinarian will probably advise you on the best ways to provide a low-stress lifestyle, a highly nutritious and easily digestible diet and perhaps supplemental vitamins if your parrot is a known carrier of the bornavirus.
There may be times when your parrot will need supplemental fluids (parenteral fluids) and medications to control vomiting and aid in intestinal transit and digestion (metaclopramide, cisapride, apple pectins, etc)
There may also be times when an antibiotics or anti-fungal drugs is desirable.
Complete recoveries or a long-term, re-stabilization are rare – but they do occasionally occur. In Florida, I once owned a scarlet macaw that returned to a stabilized (lean, but healthy) condition for over 10 years. What became of her after that I do not know.
That said, no veterinarian or owner worth their salts gives up lightly on a beloved parrot. So just about every medication has being tried (interferons, various anti-viral medications, amantadine, ribavirin, gabapentin etc.). The variability of how individual cases of PDD/ABV progress make it very difficult for me to determine if any of these treatments actually help. The closest thing I know of in traditional veterinary medicine is in dealing with FIP in cats. (ref) You can read more about various treatment options here.
Is There A Vaccine Against PDD/ABV?
No vaccine is currently available commercially although several veterinary centers have explored the possibility. Texas A & M conducted a small trial in 2010-2011 using a strain of bornavirus isolated from apparently healthy cockatiels in the hopes that that strain might be too weak to cause disease, but strong enough to impart immunity. The tests were unsuccessful – the birds eventually came down with PDD/ABV. Others have dabbled in producing a vaccine composed of parts of the virus (sub-unit vaccines) capable of stimulating immunity without causing inflammatory tissue changes. That approach seemed to work in protecting mice against mammalian bornavirus. (ref)
Tremendous resources are being committed to finding an effective vaccine against another virus that dwells in nerve tissue, human herpes virus. Perhaps the progress being made there will yield new options in developing effective vaccines against PDD/ABV as well. (ref)
Are There Ways I Can Prevent My Parrot From Catching PDD/ABV?
I mentioned earlier that our current screening tests leave much to be desired. If you can, purchase your parrots from small, conscientious aviaries that have never experienced PDD or documented a positive ABV bird.
Veterinarians do not believe that the ABV persists for very long in the environment. So the less exposure your parrot has to other parrots the less likely it is to encounter the virus. Exposure to new smaller parrots, like cockatiels and lovebirds may pose an even greater risk to your parrot. Whenever an option, check both the antibody and the virus status of any new feathered addition to your household.
Do not board birds. Hire a bird sitter to come to your home while you are away and be sure no virus are tracked in from the homes of other clients or their personal pets. Hospitalize parrots as infrequently as possible in veterinary hospitals. There is no guarantee that a species of bird other than a parrot might not also harbor the avian bornavirus.
Avoid taking your parrot to bird shows, shower and change your cloth and shoes when you return home from one.
What Will Kill The Bornavirus?
A 1:20 solution of household bleach on pre-cleaned surfaces should be sufficient.
Now That I Know That My Parrot Has PDD/ABV, How Long Will It Live ?
Current research indicates that if your parrot has tested positive for ABV or antibody against it but has no evidence of illness, it will most likely to live a long normal life. The odds of that change drastically if the bird was tested because it showed signs of poor health.
I mentioned earlier that veterinarians have seen complete recoveries or birds that stabilize – but the vast majority continue in a downward health spiral. In my experience, most parrots that show typical digestive tract or nervous system signs caused by the ABV survive less than a year. I have had a few survive up to ten years. Most of our knowledge on survival occurred before PCR and Antibody tests were available. So it is always possible that some of the long-surviving birds were incorrectly diagnosed with PDD.
This Is All So Confusing. Whose Advice Should I Rely On ?
Labs that run tests will encourage you to have as many tests as the offer run. Until we understand more about this virus and what to do with the results from these tests, I do not suggest them for healthy parrots kept individually as pets. As a pre-purchase health screen or in setting up one or two pair of breeders, it has more value. But as it it performed today, a single negative test panel may only give you a false sense of security or a needless sense of fear.