by David Hart
Forget the crackers. These birds need medical help. Their feathers rot and fall off. Sometimes their beaks crack and crumble away. Eventually, the infected parrots, macaws and cockatoos die, victims of PBFD -- psittacine beak and feather disease.
The virus that causes the deadly disease has plagued these birds in captivity and in the wild for years. However, a team from UGA's College of Veterinary Medicine has developed a test to identify the virus, and a vaccine may soon follow.
"The disease itself is not treatable. A bird that gets the virus will either kill the virus or develop the disease," said Branson Ritchie, an associate professor of small animal medicine. "A vaccine would protect healthy birds from becoming infected in the first place."
More than 40 species of psittacines -- the family of birds that also includes parakeets, budgerigars (budgies), lovebirds and cockatiels -- are susceptible to PBFD; the disease also was diagnosed recently in Australian doves. Researchers from Australia had done some "phenomenal" preliminary work describing the disease and its pathology, Ritchie said, but it wasn't until 1987 that the UGA team tracked down the guilty virus.
Before 1987, veterinarians could do little for infected birds. "I was putting eight or 10 birds to sleep per week coming out of quarantine with this disease," Ritchie said. "At that time people were discussing it as anything from a bacterial infection to endocrine abnormalities, fungal infections, stress-related factors or nutritional problems."
The virus eluded detection for years because it refused to cooperate with traditional virology methods, especially the tactic of growing a virus in a laboratory cell culture.
"Because this virus wouldn't grow in cell culture, we had to back up and use other techniques to try to recover the virus from its natural host and then use molecular biology techniques to characterize it, work with it and figure it out," Ritchie said.
What they found was something new: a very small, very hardy virus that is almost in a class by itself. Along with a handful of other viruses -- one that infects pigeons, one in pigs and perhaps one in chickens -- the PBFD virus belongs to a new class of viruses, the Circoviridae.
Armed with the same molecular techniques used to detect the virus, team member Frank Niagro of the department of medical microbiology then developed a DNA probe to test for the disease. The test can detect the virus in the bloodstream before an infected bird shows clinical signs of PBFD.
"What this allows clinicians to do is to manage the disease, in essence prevent the disease from ever being introduced to a flock," Ritchie said.
To go beyond simply managing the spread of the disease to actually wiping it out requires a vaccine. That's what they're working on now, Ritchie said. Initially, the team derived a vaccine from the tissues of infected birds, but this method has its problems.
"The virus is very difficult to kill," Ritchie said. "The only way that you could tell that a virus [in a vaccine] derived from this tissue was killed was to inject it into an animal. If the animal developed antibodies to the virus, the vaccine was good; if the animal developed disease from the vaccine, then the vaccine was not good.
"So it was not at all practical or safe to use that initial vaccine. What it gave us was a positive control, a research model, that would let us test a safe vaccine," he said.
To find a vaccine that won't infect the patients, the research team is exploring two possibilities. The first relies on the classic method of growing the virus in a cell culture; the second strategy is to develop a recombinant vaccine, in which only a piece of the virus's DNA is used. Ritchie said both methods are running neck and neck; either could produce a vaccine within the next year.
"From the perspectives of this country and Europe, neither of which has the virus in a free-ranging bird population, beak and feather [disease] can be totally eradicated by vaccination," Ritchie said.
Now that's something to squawk about.
For more information please check out http://www.vet.uga.edu/IVCVM/1998/ritchie/ritchie.htm or e-mail email@example.com