Virus-spreading mosquito expanding its reach in Minnesota

Health officials are urging Minnesota residents to empty standing water from old tires, buckets and other containers to stem the hatching of a mosquito species that is new to the state and may transmit dangerous diseases to people.

The Japanese rock pool mosquito was found in Scott County in 2007 and in Dakota, Goodhue, Wabasha and Houston counties last year. The mosquito, which hatches in relatively small pools of stagnant water, is a potential carrier of LaCrosse encephalitis virus and West Nile virus.

"We have found [the new mosquito] in several different places along the Mississippi River valley from the Iowa border to the Twin Cities area, and it could be elsewhere in the state," said Dave Neitzel, a Minnesota Department of Health specialist in diseases spread by mosquitoes and ticks.

This mosquito prefers reproducing in relatively small pools of stagnant water, Neitzel said.

"It could be a gallon ice cream pail sitting out in the woods, or a tire or two behind the garage. They could even be in a plastic tarp over a wood pile, if a pocket forms and there's water in it."

He said investigators aren't yet sure how effective the Japanese rock pool mosquito is at spreading encephalitis or West Nile. But the mosquito is a known carrier of other forms of encephalitis. In Minnesota, the tree hole mosquito has been a transmitter of encephalitis since the early 1960s. Another mosquito common in open farmland in western Minnesota is a known carrier of West Nile virus.

"The Japanese rock pool mosquito could potentially transmit both," Neitzel said. "Time will tell how important they are in passing these viruses on. But we want to get the message out now, early in the season, that if people get rid of these container habitats, it can really make a difference."

There will be no eradication efforts aimed specifically at the new mosquito, he said. If people are diligent about eliminating stagnant water from containers, the reproduction rate of the new mosquito could be cut significantly, Neitzel said.

He recommends changing the water in bird baths at least once a week. In fountains or ornamental pools, keep water moving or add goldfish to eat mosquito larvae. Rain barrels should be fitted with screens to prevent mosquitoes from using them as breeding sites.

The Japanese rock pool mosquito was first found in the United States in 1998, in New Jersey. Neitzel said the insect, which is native to Japan and Korea, likely got here in eggs that were deposited in some of the millions of tires that are shipped from Asia each year. The mosquito has since spread west and reached Minnesota, Iowa and Missouri. Neitzel said the mosquito also has been found along the West Coast in Washington and Oregon.

The new mosquito hatches a little earlier than Minnesota natives and a few may already be flying around, Neitzel said. It looks pretty much like the roughly 50 other types of mosquitoes in Minnesota, with a brownish body but signature black-and-white striped legs. It's also shy: Neitzel said that unlike the Minnesota natives that swoop in to suck some blood, "They're tentative biters that will hover for a while and look for a good place to bite.

"I recommend you just slap them," he said.

Encephalitis and West Nile cases tend to peak in mid-to-late summer. LaCrosse encephalitis affects the brain and central nervous system, and the most serious cases are generally seen in children under age 16. Symptoms include high fever, headache, confusion and seizures. Since 1985, 124 cases and one death linked to the disease have been reported to the state.

West Nile symptoms include fever, headache, fatigue and sometimes a rash. The most severe cases tend to appear in older people. Since 2002, 451 West Nile cases, 14 of them resulting in death, have been reported to the state.

Mary Jane Smetanka • 612-673-7380