Anne Minard, National Geographic News 25 Jun 08;
Even as floodwaters subside in parts of the Midwest, residents along the Mississippi River could find themselves knee-deep in another hassle: mosquitoes.
The first potential outbreaks, hatched out of the flood's still-standing backwaters, won't necessarily be the disease-carrying kind.
But mid-July marks the beginning of the prime season for the mosquito varieties that most commonly carry the West Nile virus—northern and southern house mosquitoes.
Linn Haramis, an entomologist with the Illinois Department of Public Health in Springfield, says the remaining Midwestern floodwaters could breed a bumper crop of West Nile-carrying mosquitoes—but only if temperatures are especially hot.
In that regard, flood-ravaged Midwesterners just might get a break.
Slow Start
So far this year, there have been no cases of West Nile reported in flood-affected Missouri or Illinois. But that's typical of the disease's pattern—most cases occur later in the summer.
Last year, 101 people in Illinois got sick from the disease, which causes neurological symptoms in one out of 150 infections, and four people died of it, according to the Centers for Disease Control and Prevention (CDC).
Seventy-seven people got sick and five people died in Missouri.
Only one local government in Missouri—St. Louis County—tests mosquitoes for the virus. Officials there announced on Monday that mosquitoes bearing the disease have been found in about a fifth of their samples.
"We know the virus is active," said Karen Yates, of the vector-borne disease program in the Missouri Department of Health and Senior Services in Jefferson City.
The Illinois Department of Public Health has also reported mosquitoes testing positive for West Nile in central and southern parts of the state.
Mild Summer?
The Midwest won't necessarily get a respite from the rain. Scattered storms are predicted for each of the next several days in southern Illinois and the St. Louis region of Missouri.
But the National Weather Service (NWS) predicts temperatures will be at or below normal through July in most of the flood-affected locales.
Jim Hladik, a NWS meteorologist based in Davenport, Iowa, said cool air masses have been pushing south from Canada and the Great Lakes, a pattern that is expected to continue.
"The general trend is probably near-normal to slightly below-normal [temperatures]" he said.
That may be good news for people worried about West Nile infections, which climbed in 2005 and 2006—both hot years—but dropped during last year's milder conditions.
New Breeding Grounds
Yates, the Missouri health department official, says she knows flood victims have much on their minds. But she hopes residents and cities in flood-affected areas will prepare for next month's West Nile mosquito season.
"The flooding that we're seeing now—it's not just agricultural areas or conservation areas," she said. "It's homes and businesses and communities. That brings in a whole other level of the creation of potential habitat."
Old appliances, for example, can become mosquito breeding grounds when they're left with standing water, she said.
Floodwaters also likely scoured out low-lying areas with little or no drainage, providing places for disease-carrying mosquitoes to breed.
Public health experts say they are hopeful that local governments will identify risky areas and spray low-impact larvicides as a first line of defense.
On the other hand, there's a chance the danger is no greater this year than in previous years.
Lyle Petersen directs the division of vector-borne Infectious Diseases for the Centers for the CDC branch in Fort Collins, Colorado.
He said increased risk of West Nile as a result of the flooding is going to be "minimal, if any," based on what's happened with disease-carrying mosquitoes in the wakes of past floods.
"Then again, we haven't had a flooding event like this since we've had West Nile" in the United States, he said.
The disease first appeared here in 1999.
