Lethal parrot disease may be caused by horse virus

By Ewen Callaway (Image: Susan Clubb) A devastating parrot disease that has pushed one species to the brink of extinction might be spread by a newly-discovered virus. Proventricular dilatation disease – PDD for short – deadens the nerve cells that control the oesophagus and stomach. “Birds can’t grind the seeds or digest their food properly, and they waste away,” says avian veterinarian Susan Clubb, of the Rainforest Clinic for Birds and Exotics in Loxahatchee, Florida. Veterinarians first spotted the disease in macaws exported from Bolivia in the 1970s. The illness now afflicts dozens of species of psittacines – the group that includes parrots and cockatoos – as well as macaws. Only about 70 Spix’s macaws survive today, none of them in the wild. This is in part due to PDD, Clubb says. Scientists have long suspected that a virus causes PDD. Outbreaks of the disease occur frequently, especially in indoor aviaries, and infected tissue can transmit the disease from bird to bird. But efforts to identify the cause have turned up dead ends and non-replicable results. 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.” Journal reference: Virology Journal, DOI: 10.1186/1743-422X-5-88 Endangered species – Learn more about the conservation battle in our comprehensive special report. More on these topics:
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