NEW YORK CITY—Intense public health campaigns have followed the outbreak of West Nile virus in the New York City area, but researchers at Columbia University caution that because of globalization, this "emerging infection" has the potential to become quite widespread. Panelists at a press briefing held at Columbia's Mailman School of Public Health agreed that the virus will likely remain a public health concern and that continuing efforts are needed to ensure the health and safety of the population.

A POTENTIALLY FATAL CNS INFECTION

The deaths of seven elderly residents of the New York area last year and the illness of 62 others has made West Nile virus a high-profile disease. Fourteen people have been hospitalized this year with severe central nervous system infection caused by the virus. Patients ranged in age from 40 to 87 years, and seven were male.

In the larger infectious disease context, West Nile virus is an "emerging infectious disease," and not the last of these challenges we are going to face, according to Scott Hammer, MD, Professor of Medicine and Chief of the Division of Infectious Diseases at the Columbia Presbyterian Medical Center of New York-Presbyterian Hospital. Considered an emerging infectious disease because it is a known agent appearing in a new geographic location, West Nile virus was brought to the United States by a growing trend—globalization. Increased travel, as well as ecological and environmental factors, have placed humans at increased risk of contact with previously unfamiliar microbes and their natural hosts, and thereby promote dissemination to new geographic areas.

West Nile virus is a member of the flavivirus family, of which more familiar diseases, such as Japanese encephalitis, St. Louis encephalitis (for which West Nile virus was initially mistaken), dengue, and hepatitis C are also members. West Nile virus has been found in mosquitoes as well as humans, birds, horses, and other mammals. In the West Nile virus infectious cycle, birds are the primary host; mosquitoes are the principal vector, and humans are infected incidentally. After the virus is transmitted by the mosquito to a human, the virus replicates in the local tissues and then in lymphoid tissues. Viremia ensues and is disseminated to visceral organs and the central nervous system, said Dr. Hammer.

With an incubation period of five to 15 days, the West Nile disease is marked by flu-like illness with headache, fever, rash, and severe muscle weakness. The severity of illness is a reflection of age. "By far, asymptomatic infection predominates with a minimum ratio of 1 to 100 symptomatic to asymptomatic cases," Dr. Hammer explained. "We have various ways to make a diagnosis, but we rely predominantly on antibody detection and virus isolation." As there is no specific therapy or vaccine for West Nile virus, treatment is currently only supportive. "Prevention is the key to control," stressed Dr. Hammer.

PREPARE AND PREVENT

What is the potential for the virus to spread? What is unique about the strain that was introduced into the United States, and what is its disease-causing potential? "West Nile virus sounds very exotic, but we know it's here to stay and [is now] part of the ecology of New York City," acknowledged Stephen S. Morse, PhD. Russia and Romania have experienced outbreaks of a similar strain, and the strain evidenced in this country is almost identical to that recurring in Israel, where it is "a usual fact of life," according to Dr. Morse. Dr. Morse is Assistant Professor and Director of the Program in Emerging Diseases at the Mailman School.

An emerging infection that appears suddenly and unexpectedly in the population, like AIDS or the West Nile virus, should serve as a reminder that emerging infectious diseases are very much a part of our world and will be with us indefinitely, cautioned Dr. Morse. "We will only continue to make progress if we continue in our vigilance against the many existing infections," he urged. "New York is a crossroads; because of the rapid and global movement of people and goods throughout the world, the interconnectedness of the world, we may expect to see other diseases introduced for the first time—like West Nile virus."

Dickson Despommier, PhD, believes that much like Lyme disease and rabies, "West Nile virus will become an accepted outcome of living so close to nature." Dr. Despommier, Professor of Public Health in the Division of Environmental Health Sciences at the Mailman School of Public Health and Professor of Microbiology at Columbia University, is particularly interested in the ecological connections between the spread of infectious diseases and vector-borne diseases and outlined the probable path of the virus to this country.

So where did the virus come from? The strain that appeared in 1999 in the New York area is almost identical to a strain found in Israel. There have been many outbreaks of the virus in farm geese in Israel every year, said Dr. Despommier. Infected wild birds migrating from southern Europe to Africa are attracted by the abundant feed offered at the farms. Mosquitoes transmit the virus from the migratory birds to the geese. After the birds continue on their migration, the mosquitoes then begin to infect people, initiating the epidemic.

It is further theorized that an infected individual from the Middle East entered this country via New York. Researchers were able to pinpoint the path of this carrier to a local zoo, where a number of birds became infected and suddenly died. "No birds from Africa or Europe were dying inside the exhibit, only the birds from the Western Hemisphere. That was the first clue that something unusual was going wrong," said Dr. Despommier. The epidemic then spread to other birds and animals, and eventually to humans. Dry weather conditions fostered the spread of infection in this country: Once again, as birds flew elsewhere in search of "greener pastures," the mosquitoes left behind began to infect humans. "The conditions that led up to [the epidemic] were also the conditions that led to it being stopped: Hurricane Floyd came through on September 16; changed the temperature, water conditions, and climate; and broke the dry spell," explained Dr. Despommier. Drought conditions encourage the risk of a recurring outbreak—and he suspects that the eastern seaboard and New England states can expect to see cases in the near future.

The steps the city is taking to educate and inform the public were explained by Isaac B. Weisfuse, MD, MPH, Associate Commissioner of Health at the New York City Department of Health and Associate Professor of Clinical Public Health at the Mailman School. The city has been working closely with the New York State Department of Health and the federal Centers for Disease Control and Prevention to conceptualize and implement surveillance systems to monitor mosquitoes, mosquito larvae, and dead birds and animals; to track animal infection rates; and to conduct aerial surveys of standing water and pesticide spraying programs.

Dr. Morse emphasized that although the measures being taken should serve to reassure the public, they have not eradicated the infection. Complacency would only allow for the resurgence of this and other infectious diseases. "The silver lining to this cloud is that we do have the tools…to identify both the expected and unexpected."

NR