New bug arrives in state to whine, dine ... on us

Here's the latest buzz: A new mosquito has just hit town, one that could transmit the West Nile virus and a strain of encephalititis rarely seen in Minnesota.

The Japanese rock pool mosquito was found in Scott County, where inspectors were taking a routine sampling earlier this month. The Metropolitan Mosquito Control District announced its discovery Wednesday after identifying the exotic species earlier this week. Most of the 52 mosquito species in the metro area are mere nuisances: They bite but generally don't make you sick. But about six to eight species that make Minnesota home can be health threats.

They can transmit West Nile and other viruses to humans, said Kirk Johnson, a vector ecologist for the district.

"The concern is that there's another mosquito species capable of transmitting the West Nile virus and it's [a mosquito] that people are likely to come in contact with," Johnson said.

The Japanese mosquito lays its eggs in artificial containers, such as buckets and tires, that often are found in people's back yards, Johnson said. "So they're coming out in people's yards and humans are the most convenient source for a blood meal," he said.

"Our first priority is to eradicate them from this area of infestation," Johnson said, declining to identify the specific area where the mosquito was found.

The recent onslaught of wet weather means more mosquitoes have been hatching, Johnson said. But the cooler weather means that we may be slipping past the peak season for the mosquito-transmitted virsues. That could change a bit if warmer weather sets in, Johnson said.

In their native habitat, the Japanese rock pool mosquitoes can transmit Japanese encephalitis. Here in the U.S., lab experiments show the exotic species can carry local viruses, including the St. Louis encephalitis virus. Historical records show the St. Louis virus may have shown up in Minnesota in the 1970 but it wasn't confirmed, Johnson said.

Generally that virus is carried by the northern house mosquito, which isn't very common in Minnesota.

Johnson said he and other Mosquito Control District officials weren't very surprised by this week's discovery of the Japanese mosquito in Minnesota, because "we've been anticipating their arrival for the last few seasons."

The foreign species was first discovered in 1998 in New Jersey, Johnson said. "It's been leapfrogging rapidly across states," he said.

The Japanese rock pool mosquito is the second foreign mosquito capable of transmitting local viruses to hitch a ride into Minnesota recently.

The Asian tiger mosquito was first discovered in Minnesota in 1991. The fact that it can't survive a Minnesota winter hasn't stopped its intrusion into the state; it merely hitches a ride on a truck or a train transporting containers when the weather warms.

Mosquito Control District inspectors said this week was the first time this season the Asian tiger mosquito has shown up, chalking up its third consecutive season here.

Global warming that pushes Minnesota winter temperatures higher could mean the two foreign visitors will become permanent residents.

Although it's significant that we have yet one more disease-carrying mosquito in Minnesota, Johnson said, the species is too new to the U.S. to predict how much illness it might cause in Minnesota.

No one should panic, he said, noting that there have been 32 cases of West Nile virus reported in 22 Minnesota counties this season. Considering there are more than 5 million people in the state, the risk is low, he said.

And keep in mind that of the millions and millions of mosquitoes zeroing in on human hosts, a relatively low number are infected, Johnson said.

"The highest number of any mosquito species that we've seen in one week that is infected is 3 percent," Johnson said. "The odds of becoming sick is extremely low."

Mary Lynn Smith • 612-673-4788

KEEP THE BUGS AWAY

•Wear mosquito repellent containing up to 30 percent DEET (10 percent for children).

•Wear pants and long-sleeved shirts.

•Avoid outdoor activity at dawn and dusk, peak mosquito feeding times.

•Eliminate water-holding containers such as buckets and tires from your property.

Source: Minnesota Department of Health

Mary Lynn Smith • mlsmith@startribune.com