“This spread in animals gives increased concern about what is going to happen in 2003,” says Paul Epstein, associate director of the Center for Health and Global Environment at Harvard Medical School in Cambridge, Mass. “Heavy rains could also increase the bridge vectors that carry West Nile Virus to humans and horses.”
Increasing the threat of this virus are the weather conditions inherently part of southern summers. “Hot weather speeds maturation of the virus, and increases the number of viral particles transmitted by the mosquito. In addition, hot, dry weather conditions often decrease mosquito-eating frog populations, which amplifies the problem,” says Epstein.
In 2002, West Nile Virus attacked more than 4,000 people in 44 states, Washington, D.C., and five Canadian provinces, and resulted in 284 deaths. “It might be said that the mosquito-borne West Nile Virus represents a bigger threat than SARS because it jumps species, with more than 230 types of animals, including 138 species of birds, known to be infected to date,” says Epstein.
What’s more, it doesn’t appear we have reached a plateau in the number of species affected by West Nile, says Douglas Causey, senior biologist with the Museum of Comparative Zoology at Harvard University. For example, last year in the surveillance network system about 14,000 birds were found to be positive for the West Nile virus. The Centers for Disease Control estimates the numbers could be 100 to 1,000 times greater than that, he says.
Epstein says he expects the impact of West Nile Virus to be at least that of 2002, and says environmental impacts are setting stage for greater incidences of the disease in 2003.
According to Epstein, West Nile can be transmitted through blood transfusions, organ transplants, pregnancy, and possibly breast milk. In addition, he says, neurological symptoms of the disease can persist for some time.
“The attention focused on SARS recently might be considered a little excessive, but the impacts are strong. Diseases can exert enormous forces on economics, trade, travel and tourism, as we’ve seen with SARS and West Nile,” says Epstein. “These diseases can serve as a wake-up call about the force of diseases in history.”
The reality, Epstein says SARS is one of many diseases in a group of newly emerging infectious diseases and resurging diseases. Because of the threat they pose to humans, these diseases are “sending shockwaves” through the public health system, he says.
The problem with looking at the disease picture from a strictly human standpoint, Causey says, is that we are in this together with the animals. “Infectious diseases like West Nile that can jump species can have devastating effects in animals and humans. Today, many microorganisms are jumping species in several directions. SARS, like influenza, probably originated from the genetic reshuffling of animal viruses,” he says.
Of great concern, he says, is the fact that the West Nile virus has spread to 230 species of animals and birds, including dogs, cats, squirrels, bats, horses, skunks, rabbits, and even reptiles.
“We are particularly concerned about what we’re seeing with birds. Avian deaths increased five-fold over 2001,” Causey says. “The domination of urban landscapes by generalists birds, like crows, starlings, and Canadian geese, may contribute to the spread of West Nile, along with the numerous mosquito breeding sites, such as old tires and stagnant waterways.”
To combat this increasing problem, Epstein recommends improving surveillance and response systems and developing early warning systems based on climate forecasting and monitoring of wildlife.
“We know what the solutions are,” says Causey. “We need better disease surveillance and response systems, and we need greater collaboration among wildlife, insect, human health and climate specialists.”