Pest control
The creatures of summer
bring exotic and scary diseases

By Diane Sussman
June 26, 2000

It’s the East Coast counterpart to the canary in the coal mine: three crows, all infected with West Nile virus, found dead recently in New York and New Jersey. The mosquitoborne virus, which causes encephalitis and was unknown in the Western Hemisphere before last year, killed seven elderly people and sickened 62 in the New York metropolitan region last summer.

The reappearance of the virus, which officials had hoped would not survive the winter, prompted the federal government to launch an aggressive surveillance and testing program of birds and mosquitoes in 17 states along the Eastern seaboard and Gulf of Mexico.

This will be a watchful summer for national and local health officials who, in addition to warning the public about the customary hazards of heat stroke, burns and snakebites, must contend with a growing list of exotic diseases carried by mosquitoes, ticks and rodents.

"For those of us in vectorborne illnesses [diseases transmitted through one or more insects or animals], it’s been a very busy past couple of years," said Julie Rawlings, epidemiologist with the Texas Department of Health, which is trying to thwart a second outbreak of dengue fever.

Last fall, the state experienced the worst outbreak in 20 years of this mosquitoborne illness, which had nearly been eradicated in the United States. Texas recorded 60 confirmed cases of the disorder, including a severe case of dengue hemorrhagic fever that killed a girl.

Dengue is usually characterized by high fever and joint and muscle pain severe enough to be incapacitating. Health department officials routinely caution health care practitioners to be on the lookout for unusual symptoms or clusters of the same symptoms among patients.

Texas is not alone in receiving a sobering reminder of the hazards of dengue.

According to the World Health Organization, incidence is up worldwide. Today, about 500,000 people contract dengue annually, up from fewer than 1,000 cases in the 1950s, WHO reports.

But dengue is just one piece in the pattern of rising incidence of vectorborne diseases worldwide.

According to WHO, mosquitoborne illnesses infect about 800 million people each year. More than 2.5 million die, many of them young children.

"I don’t know whether it’s better surveillance or there’s just more of it, but there’s definitely an increase in these diseases," said Tom Skinner, a spokesman for the national Centers for Disease Control and Prevention. "Certainly no one expected West Nile virus in New York City."

Expanded territory
Concerns also extend to what’s underfoot. Once confined to the arid Southwest, the potentially fatal hantavirus has migrated to California, where five cases have been reported in the past three months, officials said.

The virus is transmitted by wild rodents, primarily deer mice, who shed hantavirus into the soil through their urine, feces or saliva. Campers or hikers become infected by breathing in contaminated dust. Mono and Yolo counties, both rural, mountain communities, are considered "hotbeds," said Lea Brooks, spokeswoman for the California Department of Health Services.

The virus is rare but can be deadly, leading to hantavirus pulmonary syndrome, which starts with fever and muscle aches and can progress to coughing and shortness of breath that is severe enough to warrant intubation. There is no treatment.

Tickborne diseases, while no longer considered exotic, are becoming more common along the Pacific Coast, in the Midwest and in New England. Ticks carry Lyme disease, which sickened nearly 13,000 Americans in 1997, according to the CDC.

Ticks also carry two other diseases whose names are less well known: ehrlichiosis, a bacterial disease that is fairly new to the United States and can be far more dangerous to elderly patients than West Nile virus, and babesiosis, which is caused by a malaria-like parasite. It brings on high fevers and is responsible for the deaths of three elderly patients in Wisconsin.

Global warning
Experts attribute the upswing in exotic diseases to several factors, including global warming, global travel, a change in the distribution of disease-carrying animals and insects, human encroachment on uninhabited areas, and large populations moving to new areas.

Travel is the likely culprit in the spread of dengue fever and may account for some of the cases of hantavirus infection in California. According to the TDH, 43 of the cases of dengue fever occurred among people who had been abroad, mainly to Mexico, in the weeks before coming down with symptoms.

But officials are less clear on how West Nile virus migrated across continents. "It may have been imported on a bird," Skinner said. "We just don’t know."

After last year’s alarm bells, health officials are moving aggressively to step up education among health care workers and the general public. "We have been talking to health care workers about dengue fever for months," Rawlings said. "We want it to be in the forefront of their minds. We don’t want complacency to set in."

Health officials also are asking the public to avoid sleeping on bare ground in areas affected by hantavirus, to wear protective clothing in areas of Lyme disease and to eliminate areas of standing water where mosquitoes breed.

One of the best approaches for mosquitoes—and one that works equally well for health professionals and laypeople—is one of the simplest: a fly swatter and a sturdy screen.

"And watch a lot of TV," Rawlings said, half-jokingly. "Really. People who are inside watching TV are a lot less likely to get bitten by mosquitoes than people who are out on the porch talking to their neighbors all night."

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