Clubb, who treats birds with PDD, including captive Spix’s macaws, sent biopsy samples to a team of virus hunters at the University of California, San Francisco. Amy Kistler, a molecular biologist there, also gathered samples from veterinarians in Israel. Using a "virus chip" that can identify hundreds of different viruses lurking in a sample, Kistler's team found sequences matching one kind of virus in two-thirds of the PDD-positive parrot biopsies, and none of the negative samples. When Kistler's team sequenced viruses in parrot tissue, they uncovered 16 completely new strains of borna viruses. These typically infect the brains and nerves of horses, causing "sad horse disease" because infected equines become listless and eventually paralysed. However, the genomes of the newly-discovered parrot viruses only vaguely resemble those of horse borna viruses, suggesting the new strains might be specific to birds, Kistler says. Even the parrot viruses vary substantially from one another, and it's unclear whether geography, species barriers or other factors explain the difference, she says.
A rock-solid connection to PDD also remains provisional, without confirmation that borna viruses can cause the disease in healthy birds. "Right now we have a strong association, but we don't have causal proof," she says. While Kistler's team solidifies their case, veterinarians like Clubb are eager to put the research to use, diagnosing the disease in parrots before they get sick. "That's a tremendous breakthrough," she says. "We've been working on treatment for years, and if we catch them early enough, most of them we can return to normal." Such a test could be critical for Spix's macaw, the only member of the genus Cyanopsitta, she says. "This research could save a species, a very special species."
Source: Virology Journal
New Scientist
September 2, 2008
Original web page at New Scientist
