by: Keri Lewis
MSU Ag Communications

Mississippi State – When floodwaters recede, Mississippians in affected areas should take steps to reduce exposure to mosquitoes and the diseases they may carry.

Jerome Goddard, medical and veterinary entomologist with the Mississippi State University Extension Service, advises a common-sense approach to mosquito population control and encourages people to protect themselves from mosquito bites.

“Floods create many opportunities for mosquitoes to reproduce,” Goddard said. “There are holes left by uprooted trees and puddles created by tire tracks. Water ends up in unusual places.”

The first line of defense is reducing the mosquito population around the home by eliminating breeding sites. While most people are aware that standing water gives mosquitoes the perfect place to lay eggs, the distress caused by widespread flooding makes common practices, such as emptying buckets and birdbaths, easy to forget.

Some mosquito species are more than pests -- they can carry disease. Such is the case with the commonly occurring Southern house mosquito.

“Female mosquitoes feed on blood, and their saliva is capable of carrying West Nile Virus and other encephalitis viruses, including St. Louise encephalitis, Eastern equine encephalitis and La Crosse encephalitis,” Goddard said.

Symptoms of West Nile Virus include fever, headache, muscle aches, and nausea or vomiting, though most people who are bitten by a WNV-infected insect simply feel feverish and have a persistent headache. In more serious cases, WNV and related viruses can cause inflammation and swelling of the brain, leading to seizures, paralysis, coma and death. Other serious mosquito-borne illnesses, such as malaria, dengue and yellow fever, have been eliminated from the United States.

Wendy Varnado, entomologist with the Mississippi State Department of Health, specializes in mosquito surveillance and testing. She said in Mississippi there are five main types of viral diseases carried by mosquitoes, and the number of cases in the state fluctuates each year.

“In 2010, we had only eight cases of West Nile Virus, but we had 53 the year before,” Varnado said. “These viruses are here to stay, so people need to get into the habit of protecting themselves.”

As floodwaters recede, there are additional aggravations.

“Unlike the Southern house mosquito, floodwater mosquitoes lay eggs in the soil, and these will hatch only when inundated by water,” Varnado said. “Some species' eggs survive 3 to 10 years in the soil, so there is a huge build-up of eggs that then hatch days after the flood.”

While floodwater mosquitoes are not usually disease carriers, they are a nuisance.

“Floodwater mosquitoes are vicious, relentless biters,” she said. “Unlike other mosquitoes that are active primarily at dusk and dawn, floodwater mosquitoes are aggressive and will bite during the day.”

When water seems to be everywhere, combating mosquitoes can feel overwhelming. A few simple strategies can help reduce their numbers.

“Eliminate mosquito breeding areas around your house,” Goddard said. “Fill in or drain low spots as much as possible.”

Remove water that collects on tarps covering houses and property, clear ditches and roof gutters so water runs off properly, empty containers and objects that have collected water, and treat swimming pools or ponds with appropriate chemicals. Keep grass, weeds and vines trimmed, as mosquitoes rest in shady areas during the hottest hours of the day.

Both Goddard and Varnado recommend minimizing exposure to mosquitoes by staying inside at dawn and dusk, when these pests are most active. Wear light-colored clothing to reduce the attraction of mosquitoes and long pants and long-sleeved shirts when appropriate. Be sure window and door screens are tight-fitting. When camping or sleeping outdoors, use netting to create a physical barrier to keep out the insects.

Insecticides and insect repellants can be effective. It is important to note that some insecticides can damage plants, while others are extremely toxic to honey bees. Be sure to follow label directions and avoid spraying plants when they are in bloom.

“Insect repellants are relatively safe when used according to their labels,” Goddard said. “The Centers for Disease Control and Prevention, in conjunction with the Environmental Protection Agency, have identified the active ingredients DEET and Picaridin as effective, based on scientific trials. Oil of lemon eucalyptus is an herbal repellant and works for a short time, perhaps 30 to 40 minutes, before reapplication is needed.”

For more information on mosquitoes and related illnesses such as West Nile Virus, visit http://www.cdc.gov or look for the Extension Publication “Mosquitoes, West Nile, and Other Encephalitis Viruses: What You Can Do to Protect Yourself” at http://www.msucares.com.

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