There is no doubt the West Nile virus is here to stay, and this could be the worst year yet regarding its effects on wildlife and people. The virus now has spread from New York City to virtually every state east of the Mississippi River. Missouri, Arkansas, and Indiana reported infections in their states last year. The virus entered the New World in the summer of 1999 in northern Queens and spread out from there. It was assisted by the worst drought recorded in the area in 100 years.
How does drought foster the establishment of the West Nile virus agent, since it is transmitted by mosquitoes, an aquatic insect? Although many species of mosquitoes have been shown to carry West Nile virus and often transmit it to birds and other animals, the main vector species for the human infection is the mosquito Culex pipiens. C. pipiens is a polluted water-loving organism that prefers to lay its eggs in raw sewage. Droughts are ideal climatic conditions for C. pipiens because people are habitually sloppy with water: Witness the role standing water played in the initial outbreak in Queens. Neglected swimming pools, half-filled bird baths, flower containers at grave sites, discarded liquid garbage, etc., are all sites that attract the attention of C. pipiens. Somehow, this mosquito finds these sites, and nearby humans become victim to the bites of emerging adult mosquitoes.
The severe winter drought of 2001-2002 has attracted the attention of epidemiologists who fear a worsening of the West Nile virus story. Will the virus reach the West Coast? Will retirement communities in the far west (e.g., in Arizona, New Mexico) experience fatal epidemics? What will be the fate of the numerous species of exotic birds of Florida and Utah (e.g., the California condor)? Only time will tell. If the drought up and down the East Coast continues into the summer, will the West Nile virus ravage the entire area?
In addition to people, another source of worry is the horses. While infected horses cannot maintain levels of West Nile virus, and thus cannot serve as sources of infection for people, the mortality rate in equines is over 30 percent. For thoroughbred horse breeders, the West Nile virus has become public enemy No. 1. Fortunately, a vaccine is currently being tested that appears to offer good protection, at least in mice, against the most virulent form of the West Nile virus. Should the vaccine prove efficacious, then undoubtedly it will be given to all horses, and perhaps field trials in the elderly may commence, as well. But the development of a vaccine takes time.
What can the ordinary citizen do in the meantime? Avoiding contact with mosquitoes is the best strategy for preventing infection with any of the mosquito-borne viruses. Clean up all spills, make sure that containers around the outside of the house or apartment do not have water in them, use insect repellent when out at night (e.g., at the ball park), and use mosquito-proof screening on all windows. In 1998, no one had to worry about West Nile virus unless they traveled to an endemic center. In the spring of 2002, 283 million people will go to bed each night with one more thing to worry about. The first cases of West Nile virus this year have already emerged in Florida, infecting a few unlucky chickens and horses. The old saw that goes nature abhors a vacuum has never been more true than in todays world.
For more information about the history of the West Nile virus, see http://westnilestory.com.
Dr. Dickson Despommier is professor of microbiology at P&S and professor of parasitology at the Mailman School of Public Health. Robin Eisner, editor of In Vivo, provides editorial guidance for Point of View contributions.