Abstract
Birds, particularly crows, began dying in Flushing, New York, in late May 1999. By early June, Queens residents started bringing the dead and dying birds to a nearby veterinary clinic, where veterinarians noted that the birds suffered from neurologic symptoms such as an unsteady gait and abnormal head movements. A month later, the disease spread to the Bronx.
In August, Deborah Asnis, an infectious disease specialist at Flushing Hospital Medical Center, admitted eight people with neurologic symptoms similar to what the birds displayed. Six were admitted with encephalitis (an inflammation of the brain), and three of them died. Two had meningitis. Asnis contacted the New York City Department of Health. Initial tests indicated an outbreak of St. Louis encephalitis (SLE), a mosquito-borne viral disease.
While city health officials investigated the human cases, the mysterious disease began afflicting native and exotic birds at the Bronx Zoo. Tracy McNamara, a veterinarian and chief of the zoo's pathology department, grew concerned that birds under her care were dying. Many of them exhibited tremors, loss of coordination, and convulsions. Necropsies showed that almost all the birds had brain lesions. Many suffered from severe meningitis and/or brain hemorrhages. The findings matched the acute viral infection found in the human patients.
McNamara thought a connection between the bird deaths and human cases in Queens could exist. But not all the pieces fit together. North and South American birds are usually resistant to SLE and serve as a carrier reservoir, so the virus shouldn't have killed them. Eastern equine encephalitis (EEE), another mosquito-borne neurologic illness, was a possibility, but McNamara couldn't explain why the birds–not native to the United States and usually highly susceptible to EEE–showed no signs of the illness.
She contacted the Centers for Disease Control and Prevention. Unfortunately, they weren't interested in speaking with a veterinarian. Undeterred, she sent blood samples and tissue to the Department of Agriculture's laboratory and specimens to a contact at the U.S. Army Medical Research Institute of Infectious Diseases. These dogged efforts revealed that the disease wasn't SLE, but a different virus altogether, West Nile virus. The outbreak represented the first appearance of West Nile in the Western Hemisphere–and highlighted the critical link between human and animal health.
A zoonotic disease such as West Nile is a vector-borne illness found in wild or domestic animals that mosquitoes can transmit to humans. Approximately 60 percent of all the infectious agents that infect humans come from animals. And the percentage is much higher among newly emerging infectious diseases, including HIV/AIDS, SARS, and avian influenza.
Veterinarians should play a leading role in the public health response and biomedical research needed to contain, understand, and ultimately prevent zoonotic disease outbreaks. Unfortunately, unlike McNamara, the vast majority of them are not. Instead, most veterinarians choose to practice pet medicine. We need them to pursue careers to increase our understanding of how and why diseases spread between species. To encourage them to do so, more training grants should exist for veterinarians who want to pursue research careers or who want to do research in comparative medicine, the study of the anatomic, physiologic, and pathophysiologic processes across species–including humans.
While surveillance of humans helps identify infectious disease threats, we should budget more money for wildlife surveillance, as it is from this reservoir that many novel–and potentially deadly–infectious agents will emerge. Avian influenza surveillance serves as a success story. For the first time in human history, we are tracking the potential precursor to a human influenza pandemic. Mitigating efforts such as slaughtering infected poultry may have averted a pandemic or provided us with additional time to prepare. However, many other potential human pandemics lurk.
Scientists have identified less than 1 percent of the planet's viruses. And we can anticipate many more previously unknown infectious diseases appearing in human populations due to expanded deforestation, intensive agriculture, and the widening trade in wildlife “bushmeat.” As barriers between species continue to break down, we need more veterinarians to position themselves as garrisons on the frontlines of disease.