In late summer 1999, fifty-five people fell ill and seven of them died of encephalitis in New York State. Blood tests revealed it was West Nile Virus. At the same time, crows began dropping like the proverbial fly in parts of New York, especially Queens. The dead crows, and 20 other species of birds, tested positive for West Nile Virus that year. Mosquitoes, known to be carriers and transmitters of the virus, came under surveillance by state health departments. Major mosquito reservoirs (large, shallow swampy areas where mosquitoes breed) were tested for the virus. Sixteen mosquito pools tested positive for WNV, and all sixteen were the species Culex pipiens, which “thrives in suburbs and cities where it breeds in old tires, storm sewers and catch basins.” Throughout the course of the summer, the outbreak spread in only a 30-mile diameter from its epicenter of Queens, New York.

The West Nile Virus’ arrival in New York brought to the public attention a chink in the armor. It showed not only that serious tropical viruses could reach the United States but that public health policies and resources were not prepared to deal with heretofore non-North American diseases. The CDC acknowledges that surveillance, reporting, and response to public health issues like this one vary between states and sub regions. While New York City was showered by insecticide, other counties such as Nassau and New Jersey declined to follow suit, claiming it unnecessary to spray insecticide in an area that showed no evidence of infection. While major organizations like CDC and WHO do maintain standards for dealing with such outbreaks, interpretations of these guidelines by local and regional healthcare professionals is varied.

The inconsistency of response throughout New York in the 1999 outbreak was somewhat corrected when the virus surfaced again the next summer. Armed with a little more information and experience, health officials felt confident and prepared for the anticipated outbreak. However, the second outbreak was not exactly the same.

In September of 2000, 9 of 65 mosquito species in the New York area tested positive as carriers of the virus, compared to only one carrier species in 1999. The species differ in their breeding locations, peak season, and the organisms they tend to feed on. It would seem, therefore, that the change in infected mosquito species explains the change in secondary infected species noticed this year.

Last year, primarily wild birds fell victim; this year, bats, raccoons, chipmunks, horses and domestic rabbits entered the list of the infected state-wide. The change in carrier species also meant a change in insecticide measures. The previous year’s insecticide spraying would not suffice to control all the species involved in this year’s outbreak. Both the “where” and the “when” of the spraying would need to change.

So far this year, only 12 human cases were reported in New York State. However, a variety of animal and bird species from Canada through New England tested positive, showing an unpredicted southward and northward trend, rather than only a spread to warmer southern climates as expected. Environment Canada implemented surveillance programs for chickens, mosquitoes, and human populations, but the only reported case of West Nile Virus infection was a dead crow in Windsor, Ontario. Experts differ in opinion about the cause of the spread. Some point out that the direction of the spread follows the “well-known Atlantic flyway for migrating birds,” but no hypotheses have been thoroughly tested as yet.

At the present time it is simply Mother Nature that has kept more serious infectious diseases out of United States and Canada. The speedy mortality of lethal tropical diseases makes worldwide spread of the viruses virtually impossible. With Ebola, for example, the time between the moment of infection on the onset of symptoms is as little as four days. However, the chances of someone becoming infected in rural Equatorial Africa (the current focus of the epidemic) and getting on an international flight to the US, Canada, or Europe is limited by how long it takes for the victim to traverse dirt roads and brave the unreliable African airports.

Further, once symptoms appear, deterioration is rapid, with death resulting within one to ten days of the onset of symptoms, and often symptoms that develop on the first day are debilitating enough to prevent travel. All these things combine to keep diseases as vicious as Ebola on a short, African leash. While little is known about the West Nile Virus, in humans it has an incubation of 3 to 15 days. In mosquitoes, the incubation period is 10 to 14 days. Neither the CDC, the WHO, or any federal health agency has ventured to comment on how the West Nile Virus reached the US, given the relatively short incubation period.

Peter Brookesmith, in his 1997 book Biohazard, discusses global warming as an integral part of the spread of infectious diseases around the world, and particularly its part in the increasing risk of mosquito-borne viral diseases in the United States. Warmer conditions are moving both outward and upward in elevation around the globe. The Aedes aegypti mosquito, which carries dengue and yellow fever, usually exists below altitudes of 3300 feet, but in recent years the species has been found as high as 7200 feet. Brookesmith refers to a study in global warming which claimed that a global mean temperature increase of one degree Fahrenheit would increase the area accessible by malarial vectors from land inhabited by 45 per cent of the world’s population to land inhabited by 65 per cent.

In the case of yellow fever and dengue and its Aedes aegypti carrier, its current latitudinal limitation is 35 degrees in either direction of the Equator. If global warming advances as predicted, 5-7 degrees of latitude in both directions of the Equator could be included as Aedes aegypti territory, moving the limits of that mosquito’s range as far north as New York. Another species of mosquito that is not native to the US was imported in the mid-Eighties aboard a ship full of used tires from Japan which were laden with stagnant water.

This species, Aedes albopictus, is yet another carrier of dengue, and it spread to 17 states within two years of its arrival. Brookesmith quotes medical entomologist George Craig as saying that “all that might be necessary is for enough people to import the disease itself from places like Puerto Rico, the Virgin Islands and Jamaica to set the epidemic wheels in motion. And with the immigrant population swelling, the wheels are already greased.”