West Nile Virus Claims More Lives

By Cat Lazaroff

WASHINGTON, DC, August 15, 2002 (ENS) - The number of U.S. human cases of West Nile Virus is rising, with new cases now reported in Florida, Mississippi, Maryland, Massachusetts and Washington DC. While most states are combating the virus with low impact tactics such as larvicides, and advising residents to take steps to avoid mosquito bites, some states are taking the controversial step of spraying pesticides.

Mississippi State Health Officer Dr. Ed Thompson reported the first death from West Nile virus in the state on August 12, followed the next day by the announcement of another death. Officials have now tallied 48 human cases in the state. The watery southern region has been hard hit, with neighboring Louisiana confirming that seven people have died from the virus this month.

On Wednesday, Maryland announced the state's first human case of West Nile virus (WNV), an 80 year old man who has tested positive for the mosquito borne disease. The unidentified man was hospitalized on August 1 with symptoms of encephalitis, a swelling of the brain, but has since been discharged and is recovering, according to the Baltimore Health Department.


The mosquito Culex pipiens is the primary transmitter of West Nile virus in the United States, though other mosquito species can also carry the disease. (Photo courtesy National Safety Council)
In nearby Washington DC, a 55 year old man remains in serious condition after being diagnosed with West Nile virus on August 7. The man, whose immune system is weakened by leukemia, remains at the National Institutes of Health hospital in Bethesda, Maryland. His is the only confirmed human case of the virus in the District of Columbia this year.

Two other states have recently reported their first 2002 cases of the disease. A 38 year old woman in Massachusetts was diagnosed with West Nile virus earlier this month after a 10 day visit to Missouri, where she is suspected to have contracted the disease. There were three confirmed human cases of West Nile virus in Massachusetts last year.

And in Florida, the first human West Nile virus case of the year is an unidentified Sumter County resident who may have contracted the disease in Louisiana.

Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. Infected mosquitoes can then transmit West Nile virus to humans and animals while biting to take blood. The virus is located in the mosquito's salivary glands. During blood feeding, the virus may be injected into the animal or human, where it may multiply, possibly causing illness.

According to the Centers for Disease Control, there have been 156 confirmed human cases of WNV so far this year, including nine deaths - two in Mississippi and seven in Louisiana, site of the worst outbreak of the disease, with 85 confirmed cases this year.

Mississippi has the second largest number of WNV cases, with 48 confirmed or probable human cases and two deaths.


A Culex mosquito on a human finger. (Photo courtesy CDC)
Nationwide, 34 states have had confirmed cases of West Nile virus since the disease first appeared in this country in 1999. The disease has now claimed 27 lives, out of a total of 305 confirmed cases.

States have adopted a variety of tactics to reduce the risk of additional West Nile virus infection. Most involve attempts to cut mosquito populations by eliminating their breeding sites and treating water sources to kill mosquito larvae.

Through a special surveillance program initiated by the Centers for Disease Control (CDC), 49 states, five cities and the District of Columbia are now monitoring the disease by testing wild birds, sentinel chicken flocks, veterinary cases, mosquitoes and their breeding areas.

Where pools of infection are found, some states are using larvicides - special pesticides that target mosquitoes in their larval, water dwelling form. In Washington DC, for example, city health department workers treated 1,161 water catch basins with larvicides after the city's first human case was diagnosed.

Washington DC workers also launched a massive public education campaign, visiting 7,000 houses in the area where most infected birds and mosquitoes had been found to distribute information on how to eliminate areas where mosquitoes breed, and how to avoid mosquito bites.

"By the end of the day, we will have reached homes in every ward of the city, and I'm very, very proud of that," said Washington DC Mayor Anthony Williams on Wednesday.

The CDC recommends that residents police their property for standing water sources where mosquitoes may breed, including rain gutters, bird baths, open garbage cans, window wells and swimming pools. To avoid mosquito bites, the CDC recommends that adults use bug repellent containing at least 10 percent DEET (N,N-diethyl-meta-toluamide). Children should use repellents with less than 10 percent DEET, and children under two should not use repellents at all, the agency says.


Water standing in a pail is a perfect mosquito breeding ground. (Photo courtesy CDC)
Most states have adopted these guidelines as well, and say that such citizen actions are the best way to reduce WNV cases.

"Mosquito control remains one of the oldest and most basic public health activities," said Mississippi's Dr. Thompson.

A few areas are taking an aggressive approach to mosquito control: spraying to kill the adult insects. On Wednesday, the Pennsylvania Department of Environmental Protection (DEP) announced plans to spray in one Bucks County community where DEP sampling has shown unusually large numbers of mosquitoes.

"Adult mosquito control is an unusual step for us to take, but we feel it is better to be out front in dealing with the large mosquito population we face this summer," said southeast regional DEP director Joseph Feola. "Spraying will be directed onto vegetation and in wooded areas. The pesticide has no impact on human health and breaks down very quickly in the environment."

"Normally, we control the West Nile potential and mosquito population by controlling mosquito larvae," Feola added. "But with the wet weather much of the state experienced in May, producing high numbers of adult mosquitoes, and the presence of the virus we decided spraying for adult mosquitoes is appropriate at this time in these municipalities."

In New York, two Queens neighborhoods were sprayed last night from trucks. Spray trucks have been operating for weeks in Florida and Louisiana as well.

The Pennsylvania DEP is using backpack sprayers, other areas are using spray trucks, and in past years, some regions have used planes to spray pesticides from the air. All of these spray techniques can do more harm than good, warn environmental and public health groups.

The Safer Pest Control Project, a non-profit group dedicated to reducing pesticide use and implementing safer alternatives, warns that spraying pesticides will not eliminate mosquitoes. Spraying does not reach many enclosed areas, the group says, and does not affect mosquitoes in the egg, larva or pupa stages, leaving new mosquitoes to hatch out within 12 to 16 days.

Mosquitoes can also become resistant to the pesticide sprays after repeated exposures, the group warns. As mosquitoes become resistant, increasingly toxic chemicals may be used to eliminate them.


Thirty-four states and the District of Columbia (shown in orange) have had confirmed human cases of West Nile virus since 1999. States where people have died from the disease are cross hatched. (Map courtesy CDC)
The Environmental Illness Society of Canada argues that pesticide spraying "presents a significantly higher risk to the health of the general population than the risk posed by WNV," because of the toxicity of many pesticides.

Other groups warn that pesticide spraying can devastate local insect populations, including harmless and beneficial species.

"The seductiveness of aerial pesticide spraying, devastating to butterflies and other non-target species, and frightening and potentially harmful to many humans, should be the last, not the first, approach to controlling disease spread," wrote Michael Gochfeld, professor of environmental and community medicine at the Robert Wood Johnson Medical School and School of Public Health, in the summer 2000 issue of the journal "American Butterflies."

"Spraying to control adult mosquitoes is considered a last resort to be used only when local infestations become a serious nuisance or health threat," Gochfield added.

In April 2001, an international group of health experts met at a conference sponsored by the New York Academy of Sciences to share reports and new studies on WNV. Citing epidemic outbreaks of WNV in Israel, Russia, Romania and South Africa, the experts agreed that surveillance, public education, eliminating breeding sites and targeting mosquito larvae were the best tactics for controlling WNV outbreaks.

Almost no one argued for pesticide spraying targeting adult mosquitoes.

An overview of West Nile virus information and issues is available at: http://www.nyas.org/scitech/sum/conf_01_0405_2.html

The Centers for Disease Control and Prevention's West Nile virus website is located at: http://www.cdc.gov/ncidod/dvbid/westnile/index.htm