West Nile may become bigger threat

West Nile virus is likely to be a bigger threat this summer than it was last year, according to a variety of experts who spoke at a conference in Baton Rouge April 30.

Citing the spread of the virus across a large portion of the country in just four years, officials said West Nile is changing the way many people look at the threat of mosquito-borne diseases.

Those comments and many more came during the 2nd Mosquito-borne Diseases in Louisiana Conference. The conference was coordinated by the LSU AgCenter, and other sponsors were the Louisiana Department of Health and Hospitals' Office of Public Health, the Louisiana Department of Agriculture and Forestry and the Louisiana Mosquito Control Association.

Among the experts from across the country who shared their perspectives on mosquito-borne diseases and ways to protect against them was Dr. Roger Nasci, a research entomologist with the Centers for Disease Control and Prevention.

“We only have a four-year history with West Nile virus,” Nasci said, pointing out that a variety of other mosquito-borne diseases, such as St. Louis encephalitis, eastern equine encephalitis, western equine encephalitis and LaCrosse encephalitis, have been around much longer. “But our experience shows that West Nile virus is changing the complexion of arboviral cases.”

Nasci pointed out the United States' first reports of West Nile virus in 1998 were confined to 26 of the 4,000 or so counties in the country. Four years later, the virus was found in 1,947 counties — and had spread to 42 states and the District of Columbia.

The CDC researcher said some mosquito-borne diseases have gone through a cycle where spreading increased rapidly and then declined as control efforts or other measures came into play. One such virus was St. Louis encephalitis. “Our concern is that West Nile virus is not going to be like St. Louis encephalitis (in leveling off and/or declining after a few years) but that it is instead going to be a more significant public health threat,” Nasci said.

Nasci wasn't alone in that concern. State epidemiologist Dr. Raoult Ratard of the Louisiana Department of Health and Hospitals said he expects the number of reported West Nile virus cases in the state to increase this year.

“I think you are going to see the same sort of pattern — but worse this year,” Ratard said, and he provided an example.

“There are 24 parishes with birds or mosquitoes that have positively tested for West Nile virus,” Ratard said. “Last year, there were only four at this time.”

Louisiana saw 329 human infections and 24 deaths from West Nile in 2002. No human cases have been reported so far this year, but officials say the virus appears to be spreading across the state again this season.

“Louisiana was one of the leading states in the number of West Nile virus cases and deaths in 2002,” said Dr. David Boethel, associate vice chancellor of the LSU AgCenter. “Our experience with St. Louis encephalitis in 2001 and West Nile virus last year makes it clear we have to do something to control mosquito-borne diseases.”

Boethel and others said that's why the LSU AgCenter has worked with state agencies and other organizations to form a mosquito control outline known as LaMAP, which is short for Louisiana Mosquito Abatement Plan.

That plan is being introduced to public officials and citizens across the state this spring with the hopes it will spur the state's 44 parishes that don't have organized mosquito abatement programs to move in that direction.

“The least expensive method of reducing mosquito-borne diseases is prevention,” said Madelyn McAndrew, assistant secretary of the Louisiana Department of Health and Hospitals' for its Office of Public Heallth. “It needs to become automatic for everyone to think about prevention.”

The state department is one of the partners in the LaMAP plan, as well as a variety of cooperative research and educational programs aimed at mosquito prevention and control.

Officials participating in the conference this week agreed such prevention methods as mosquito control and other means of protecting people from mosquito bites are the major ways to avoid the spread of West Nile and other mosquito-borne diseases in humans.

“Don't ask me why there's a West Nile vaccine for horses but not for humans,” said state veterinarian Dr. Maxwell Lea of the Louisiana Department of Agriculture and Forestry, while commenting on the effects such diseases have on animals. “But I have to say that we've had a hard time getting people to vaccinate horses even though an effective vaccine is out there.”

Tom Merrill is News Editor for LSU AgCenter Communications. ([email protected])

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