| [Image: mosquitoes in dish] |
| [Image: old tires] |
| [Image: mosquito trap] |
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.
Louisiana is host to several mosquito-borne diseases including St. Louis encephalitis, eastern equine encephalitis, LaCrosse-California encephalitis and most recently, West Nile virus. This virus was first reported in Louisiana in 2001. By 2002, the state reported more than 300 human cases of West Nile virus and 25 deaths. Since then, the number of reported cases and deaths has dropped off.
Mosquitoes early in the spring aren’t as dangerous as West Nile virus vectors as mosquitoes later in the summer. The mosquitoes that transmit West Nile virus over-winter as adults, so populations aren’t high until late summer. The prime time for West Nile virus to be spread is late July through September.
“In Louisiana, West Nile is carried mostly by urban mosquitoes during a long season,” said Wayne Kramer, LSU AgCenter entomologist and mosquito biologist. Kramer said researchers across the country are learning more about mosquito ecology and control.
Kramer said West Nile virus infections go in cycles. They start with rather large outbreaks of the disease. As people build immunity, the occurrence of the disease will diminish. Then, when a new generation of people without immunity comes along, the cycle may start over again. Many people will develop immunity by having been exposed to the disease but never display any symptoms. Others may have mild, flu-like symptoms, while still others may experience encephalitis or meningitis and require hospitalization.
“People with a milder case of the disease may never be diagnosed,” Kramer said. “We see a whole gradation of responses in the human population. Most people develop antibodies and never know they’ve been exposed.”
The best method of identifying 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 have been working with the Louisiana Department of Health and Hospitals to help 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 are doing more 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,” Kramer said. “They serve as a source of information, and most aren’t affected by the virus. Unfortunately, testing wild birds is labor-intensive. “The primary, most effective sources are mosquitoes themselves.”
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,” Kramer 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.
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.
(This AgCenter Lead was updated on June 5, 2008, by Linda Benedict.)