Bird Ailment Study May Yield AIDS Clues

During an unusually icy January in the Maryland suburbs, red finches started showing up with grotesquely swollen, crusty eyes.

The eastern house finch is normally a scrappy, social species. But in those early weeks of 1994, infected finches struggled to find sunflower seeds with fading sight. They sat alone on the bird feeders, feathers ruffled, while healthy birds flitted away to roost in nearby trees.

Within weeks, sick finches were reported far beyond the Washington area where they were first observed. By the end of the year, they had been spotted all over the Eastern Seaboard.

Now, scientists hope to use what they are learning about the finch eye disease to expand understanding of a growing number of epidemic diseases in humans, animals and plants.

The project is funded by a five-year grant from the National Institutes of Health, one of 12 chosen by the NIH and other federal agencies to investigate the ecology of infectious disease. The studies will examine how environmental changes such as habitat destruction, global warming and pollution may cause new diseases to emerge and old ones to become more deadly.

“An unusually large number of new diseases have emerged in the last 20 years or so, not only in humans, but in animals and plants as well,” said ecologist Andre Dhondt of the Cornell Laboratory of Ornithology in Ithaca.

He cited AIDS, Ebola, drug-resistant tuberculosis, mad cow disease and other spreading plagues.

“This is probably the first study ever where it has been possible to study in great detail a newly emerging disease in a natural population,” Dhondt said.

In the case of the finches, scientists at the University of Georgia and North Carolina State found the birds were infected with a new strain of Mycoplasma gallisepticum--or MG--a bacterium that is a common cause of upper respiratory infections in chickens. It had never been seen in songbirds.

“The goal is not to know about house finches and Mycoplasma,” Dhondt said. “The goal is to develop a mathematical model that allows us to identify what we need to measure and summarize what we’ve found.”

The model can then be applied to other diseases.

“One of the interesting things about Mycoplasma in house finches is that it has many similarities to AIDS,” Dhondt said. “Understanding how we can fight this disease in finches might help us understand how to treat similar epidemics in humans.”

Bird watchers and ornithologists were alarmed at how swiftly the disease was spreading. They feared migrating finches would infect songbirds in the tropics.

At Cornell, Dhondt’s research team enlisted the help of Project FeederWatch, a nationwide army of backyard bird watchers.

The collaboration of professional researchers and more than 8,000 “citizen scientists” found the infection reduced the eastern house finch population by 60%--180 million birds--within 2 1/2 years.

There are many unanswered questions. Why is the disease wiping out house finches, but not sparrows or cardinals? Why has it persisted? Why haven’t finch populations recovered? Why are house finches in the eastern United States severely affected, while western populations are, so far, virtually untouched?

At a Cornell University field lab in Ithaca, Elliot Swarthout captures finches in a feeder trap to collect data. He weighs them, swabs their eyes to test for disease, takes blood samples, attaches leg bands and releases them. He outfits some of the birds with tiny radio transmitters to monitor their travels.

Inside the lab, a graduate student observes small flocks of wild finches housed temporarily in a room, recording their behavior to see if social dominance affects disease resistance.

In researcher George Kollias’ lab at Cornell’s veterinary school, house finches are intentionally infected with Mycoplasma then kept in cages where they are fed and protected from the elements and other diseases.

The goal is to see if birds would recover from the blinding infection if they weren’t killed by starvation or predators first.

Several factors appear to make eastern house finches more vulnerable to the epidemic, Dhondt said. One is inbreeding.

House finches are native in the West and were trapped and sold as “Hollywood Finches” in the East in the 1930s, until federal law prohibited sale of American songbirds. The eastern population is descended from a small number of captive birds released in 1940 in New York City.

Another contributor is the eastern house finch’s behavior. Western house finches are desert birds, but in the East, the brown-streaked females and rosy males are primarily suburban birds that congregate at feeders.

Eastern house finches also are highly mobile, spreading infection rapidly over a wide area.

“Will it move to the West? We don’t know,” Dhondt said. “Our model should help us predict that.”

Researchers in Ithaca, Atlanta and at Princeton University also are exploring the extent to which stress makes the birds more susceptible, Dhondt said.

“One of the things we’re speculating about is why we find a peak of disease in February,” Dhondt said. One theory is that as they prepare for springtime mating, the birds are physically stressed.

Dhondt said he expects the studies will produce a more detailed understanding of the disease in two to three years.

“What’s so interesting about this system of Mycoplasma in house finches is the degree to which we will be able to understand the strange dynamics of host and disease,” Dhondt said.

“When you study one particular thing in phenomenal detail, you always hope what you learn will apply to other systems and help you build theory,” he said. “That’s really why we do research: to understand the world around us.”