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Saving the world's parrots from killer disease
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A heinous disease has been killing parrots since the 1970s. First known as Macaw Wasting Disease, it has since been discovered in as many as 50 bird species. It's now known as Proventricular Dilatation Disease or PDD.
Dr. Ian Tizard is Professor of Exotic Bird Health at the Schubot Exotic Bird Health Center at Texas A&M University. He is also the center's Director.
“PDD is a killer primarily of big valuable precious birds – the macaws, conures, african greys and to a somewhat less extent, amazons and cockatoos. The significance lies in the fact that many of these birds are highly endangered and obviously losing any of them is a great tragedy. Over the years it's been widely believed that PDD was an infectious disease. It was almost certainly viral, too, because if it was bacterial it could have been fixed with antibiotics. But the virus proved incredibly difficult to identify,” Tizard said.
Although no one can say for sure where PDD originated, Australian birds like cockatiels seem to be very resistant to the virus and may have evolved with the virus. It implies they are better able to handle the virus than South American or African birds, Tizard said.
Researches identify virus
Last year the University of California at San Francisco and Columbia University announced the discovery of the virus thought to cause PDD. They named the new virus Avian Borna Virus, or ABV.
Some avian professionals and bird owners question whether the Avian Borna Virus actually causes PDD. A&M's research data indicates the virus does indeed cause the disease, Tizard said.
“Certainly it's clear to me that ABV is sufficient to cause the disease, but I don't know what triggers the disease.”
“In classical PDD involving the intestine, it appears that Avian Borna Virus destroys the nerves leading to the intestine. This results in paralysis, blockage of the flow of food, failure to absorb nutrients, starvation and death. Eventual cause of death is probably destruction of brain cells. We also see cases with damage to the nerves leading to the heart, possibly leading to heart failure. We certainly see cases affecting the optic nerve and eye resulting in blindness. “
“We see a great diversity of clinical signs depending on just what part of the bird's nervous system is damaged by the virus. We also see differences in the amount of damage that appears to be lethal. Some birds die with really severe lesions, (as seen during) necropsy and some with relatively mild lesions. Some die after 55 days, some after 110 days and possibly longer. I have no idea what determines survival time or lesion severity. It might be the type of virus, we now have 6-7 different genotypes. It might be due to the species of bird.”
Testing for ABV
There are currently two tests to detect the virus – a blood test and a fecal test. Texas A&M offers the fecal test, which produces results faster and, at $30, is affordable. However, since certain birds, like cockatiels and african greys, are intermittent shedders of the virus - meaning the virus is not always in the feces - Tizard recommends the feces be collected throughout a three week period, mixed together and tested. "A single negative test is not significant. Multiple testing will be needed to provide assurance that a bird is truly uninfected." It is not known for certain if many other species of birds also shed the virus intermittently.
Some birds can also be carriers of the virus, meaning that they can have the virus, but not develop PDD right away and researchers don't yet know why.
“We have seen several examples of infected birds living apparently healthy, normal lives for more than a year. Then suddenly, for no apparent reason they sicken and die. I have no idea what triggers disease and death. These birds are shedding virus in their feces and probably nasal secretions but do so intermittently. We have seen this in african greys, cockatiels and severe macaws."
“Clearly infection with ABV is not sufficient by itself to cause the disease, at least in some species. What then pushes the bird into the full blown disease, we don't know.” Researchers have found that mated pairs of birds can even live together without one of them being infected with ABV thus far. “There's clearly something we're missing about the virus.”
How the virus spreads
The virus can be transmitted when a bird injests feces from an infected bird, Tizard said. It appears there are other ways of spreading the virus. Tizard's research team has found the virus in many areas of a bird's body, such the mouth, the brain, the eyes, the nose, and in the cloaca, which is a tube-like structure through which reproductive fluids/eggs, feces and urine pass in birds. "Some of these birds seem to be oozing the virus from every pore." It's not known how much virus it takes to infect a bird.
“The virus has also found on a bird's plumage or a least on its preen gland,” Tizard said. If the virus is found on the plumage, then it could be airborne and studies are underway to see if ABV could be transmitted that way, but Tizard thinks it is contagious and spreads easily.
And that poses risk to healthy birds that have been around or exposed to infected birds.
Next article: Saving the world's parrots, part II
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