Don Ganem (left) and Joe DeRisi (right) weren't planning on studying a bird disease, but an enterprising postdoc and similar pathology to a human ailment moved them to take a closer look and pinpoint the virus that causes PPD.

Since then, Ganem and DeRisi had received stacks of entreaties from researchers wanting to tap their technology. In 2006, two unusual requests arrived. Both asked the researchers to help unravel the mystery of a parrot disease, PDD.

“Parrots seemed kind of off the subject, so at first we just filed the letters,” Ganem recalls.

At the time, Kistler was studying upper respiratory illnesses with the Virochip, but she had a growing interest in animal viruses. When she got wind of the letters, she read up on PDD and discovered the disease first appeared in macaws imported to the United States from Bolivia in the 1970s. Since then, veterinarians had recorded it in more than 50 species of Psittaciformes, the avian order that includes many pet species, such as parrots, macaws, cockatoos, cockatiels, lorikeets, parakeets, budgerigars, conures, parrotlets, and lovebirds. The disease jumps between birds in close contact, suggesting an infectious agent.

Under the microscope, veterinarians see tiny round specks in tissue from sick birds, specks that resemble virus particles. Veterinarian Susan Clubb had written one of the letters pleading for a viral investigation of PDD. “For a very long time, researchers all over the world have been trying to find the agent that causes the disease,” says Clubb, who has a bird clinic in Loxahatchee, Florida. “It's been very elusive.”

Clubb calls PDD an obsession. Over her 30-year career, she's treated hundreds of birds with it. She's watched PDD wipe out whole indoor aviaries in Canada and the northern United States. “It's devastating,” says Clubb, who counts 280 parrots in her own breeding flock.

Like AIDS, PDD is a wasting disease. Inflammation attacks the nerves at the base of the proventriculus, paralyzing the organ. As the organ swells, birds stop eating, regurgitate, and pass undigested food in their feces. Affected parrots often become clumsy and fall off their perches. Seizures sometimes strike. But symptoms can wax and wane, and birds might rally for a time after treatment for secondary bacterial and yeast infections.

Most cases are diagnosed symptomatically. Owners sometimes spring for an arduous and costly crop biopsy, in which veterinarians search for tell-tale inflammation of the gastrointestinal nerves. Even then, biopsies miss about half of positive cases, says Clubb. A definitive diagnosis—as confirmed by the inflamed nerves—can be made only via necropsy.

There are cultural parallels to AIDS, too. PDD is freighted with stigma. No breeder wants a reputation for keeping birds with the disease. Organizations of parrot lovers have sprung up to raise awareness, some launching a campaign called Stop PDD, which made a PDD quilt, each square hand-sewn to recall a parrot that had passed.

As Kistler discovered, parrot breeding is a big backyard business, exploding after a 1992 law banned the importation of most wild parrots. Now, virtually all the estimated 12 million pet parrots in the United States are captive bred, providing income for several thousand breeders, according to the American Federation of Aviculture. Rare, hard-to-breed, “super-exotics,” such as the magnificent hyacinth macaw, can fetch $10,000 to $15,000. African grays, known for their intelligence and longevity, typically cost $1,200 retail.

Ganem delved into the pathology of the parrot disease to determine whether it resembled any human ailment. He made a connection with a condition called achalasia. In this disease, the esophagus—analogous in form and function to the proventriculus of birds—is affected, impairing the peristalsis that normally propels food along the digestive tract. The cause is unknown, but esophageal biopsies of achalasia patients show “active inflammation of the nerves and ganglia,” Ganem says, “which in fact is the exact pathology of PDD. I realized this wasn't just important for parrot owners, it actually had relevance to human disease.”

Photos: Lenny Gonzalez

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