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Mosquitoes pose threat: Keep their numbers down

Mosquitoes buzz around Louisiana every day of the year. More than 60 species inhabit the state. The tropical and subtropical climate in Louisiana creates conditions that support mosquitoes year-round. And while many are benign, some are carriers – or vectors – of several worrisome diseases. Female mosquitoes need a “blood meal” from a human or animal, often a bird, before they can lay eggs. And as they move among these hosts taking their blood, they may spread viruses and other agents that cause diseases.

Recent rains could cause a surge in the mosquito population. Read more.

Louisiana is host to several mosquito-borne diseases including St. Louis encephalitis, eastern equine encephalitis, LaCrosse-California encephalitis and most recently, West Nile virus.

West Nile virus was first detected in the United States in 1999 and in Louisiana in 2001. The virus can cause severe clinical disease in humans and horses. While human cases continue every year across the country, horse cases have dramatically declined because of the development and widespread use of an effective equine vaccine.

Since its detection n Louisiana in 2001, more than 1,000 cases and 63 human deaths have been reported to the Louisiana Department of Health and Hospitals through 2009. Many human cases result in a mild fever and flu-like illness and are never reported. Severe cases can result in encephalitis or meningitis, and deaths attributed to West Nile virus have been recorded in Louisiana every year since 2002. The cases occur across the state and, on a yearly basis, typically peak in July and August when vector mosquito populations are most abundant.

In Louisiana, West Nile is carried mostly by urban mosquitoes during a long season. The best way to identify mosquitoes with West Nile virus is to collect them and test them for the virus.

A group of AgCenter entomologists, extension agents and other faculty members worked with the Louisiana Department of Health and Hospitals to establish mosquito abatement districts in Louisiana parishes that don’t have them. Some parishes have had mosquito control districts since the 1960s. Others have established districts more recently when the West Nile virus began to be seen as a problem. And some still haven’t developed a mosquito control district.

Local mosquito control districts in Louisiana do wild bird surveillance, using nets or baits to catch, sample, band and then release the birds. 

“Wild birds are a good indicator for viral activity,” said Lane Foil, LSU AgCenter entomologist . “They serve as a source of information, and most aren’t affected by the virus.”

The AgCenter is learning more about the spread of West Nile virus by studying the relationships between mosquitoes and birds. Researchers are tapping both mosquitoes and birds to see which birds the mosquitoes feed on. They’re also tracking bird counts and mosquito populations to discover if there are relationships between different species of mosquitoes and different types of birds.

“Abundance is as important as the kinds of birds,” Foil said. “There’s still a lot we don’t understand as well as we would like to.”

Because the West Nile virus thrives in hot temperatures, late summer is the most dangerous season. Experts recommend practicing source reduction – altering mosquito breeding sites or potential breeding sites to make them less hospitable for mosquitoes. Some of these include:

  • Remove water-holding containers, such as tires and other debris.
  • Keep flower pots and similar yard and patio containers empty of standing water.
  • Drain ornamental ponds or swimming pools no longer being properly maintained.
  • Fill low-lying depressions to eliminate standing water.
  • Ditch to promote rapid runoff of rainwater.

Of concern now is the threat of dengue fever, which has been confirmed in Florida.

“We haven’t had cases of dengue transmitted in the continental United States in 50 to 60 years.” Foil said.

Because West Nile virus is now an established virus, Foil fears the same thing could happen with dengue virus.

Helpful links:

LSU AgCenter West Nile Virus fact sheet

Centers for Disease Control West Nile Virus site

National Biological Information Infrastructure West Nile Virus page

Louisiana Department of Health and Hospitals West Nile Virus site

Taking the bite out of mosquitoes

The LSU AgCenter is one of 11 institutions of higher education in the Louisiana State University System. Headquartered in Baton Rouge, it provides educational services in every parish and conducts research that contributes to the economic development of the state. The LSU AgCenter does not grant degrees nor benefit from tuition increases. The LSU AgCenter plays an integral role in supporting agricultural industries, enhancing the environment, and improving the quality of life through its 4-H youth, family and community programs.

Last Updated: 8/1/2011 7:44:09 AM

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Bogren, Richard C.
LSU AgCenter