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Published June 03, 2009, 12:00 AM

New mosquito threat emerges

Faced with a new mosquito species that could transmit disease in Minnesota, state health and mosquito control officials are urging residents to rid their property of water-holding containers.

Faced with a new mosquito species that could transmit disease in Minnesota, state health and mosquito control officials are urging residents to rid their property of water-holding containers.

The Minnesota Department of Health (MDH) and the Metropolitan Mosquito Control District (MMCD) confirmed that the Japanese rock pool mosquito (Aedes japonicus) is established in at least five southeastern Minnesota counties.

This mosquito could potentially transmit LaCrosse encephalitis virus (LAC) and West Nile virus (WNV) to humans.

"Spring is the perfect time to take simple steps to prevent mosquito-transmitted disease later this summer," said David Neitzel, an MDH epidemiologist who specializes in mosquito-borne diseases. "Several types of disease-carrying mosquitoes use water-holding containers, such as old tires, buckets, or cans, as breeding sites. If everyone dumps the water out of these containers and removes them during their spring yard work, we can reduce the number of mosquitoes that could transmit disease later this summer."

The Japanese rock pool mosquito, an Asian mosquito that was accidentally imported into this country, has been steadily moving across the United States since it was first found in New Jersey in 1998.

It was first identified in Minnesota in Scott County in 2007. During 2008, it was also detected in Dakota, Goodhue, Wabasha and Houston counties.

This spring, it was determined that these mosquitoes' eggs had survived the Minnesota winter.

"We suspect that we will soon find this mosquito in other counties as well," Neitzel said.

LaCrosse encephalitis is usually transmitted through the bite of an infected Eastern tree hole mosquito (Aedes triseriatus), a daytime feeding mosquito common to much of southern Minnesota.

This mosquito also uses water-holding containers as breeding sites. These same containers are also used by some types of Culex mosquitoes that maintain West Nile virus in the environment, but don't commonly bite people.

Removal of water-holding containers will control all three types of mosquitoes and help prevent both LaCrosse encephalitis and West Nile virus.

Here are some spring-cleaning tips that can help prevent mosquito-borne disease this summer:

•Inspect your yard, surrounding brush and woods, and neighborhood for any containers (e.g., tires, buckets, cans) that can hold a small amount of water.

•Properly dispose or recycle any unwanted containers and store all other containers indoors so they do not collect water.

•Change the water in bird baths and animal watering bowls or troughs weekly.

•Keep water moving in fountains, ornamental ponds and water gardens, or stock fish that eat mosquito larvae.

•Make sure that unused swimming pools, fountains, and boats are kept completely drained of water.

•Make sure that tarps do not collect pockets of water.

•Unclog rain gutters to ensure proper drainage.

•Be sure rain barrels are fitted with screens to prevent mosquitoes from using them as breeding sites.

•Check your trees for pockets of standing water. Often water collects between trunks or where a branch joins the trunk. Drain any water found and fill the pocket with sand.

Most of the mosquitoes produced in containers do not fly far from where they develop, so home cleanup helps to protect family and neighbors from mosquito-transmitted disease.

LaCrosse encephalitis affects the brain and central nervous system.

Severe cases occur primarily in children and adolescents younger than age 16 and are characterized by symptoms like high fever, headache, confusion and seizures.

Since 1985, 124 LAC cases (including one death) have been reported to MDH.

Most WNV cases experience fever, headache, fatigue, and sometimes a rash.

Severe WNV encephalitis cases tend to occur in older people, rather than children or adolescents. Since 2002, 451 WNV cases (including 14 deaths) have been reported to MDH.

Information on LAC, WNV, and mosquitoes can be found at the MDH website: and the MMCD website:

People who have questions about mosquito-transmitted diseases can call MDH at 1-877-676-5414 (outstate) between 8 a.m. and 4:30 p.m. Monday through Friday.