States Prepare for West Nile Season

May 26, 2008— -- SIOUX FALLS, S.D. (AP) - Officials have found that controllingWest Nile virus is as much about educating the public as it iskilling mosquitoes.

South Dakota, with the nation's highest rate of seriousinfections, is entering its seventh summer of the sometimes fatalvirus that is transmitted by mosquitoes from infected birds tohumans.

Not every mosquito species transmits the virus. Early in springit's a nuisance mosquito called Ades vexans that's bothering peoplein the eastern part of the state but seldom carries the virus. It'sfirst to show up because eggs laid in fall hatch in spring.

"Just add water and poof, you've got mosquitoes," said MikeHildreth, a professor and researcher at South Dakota StateUniversity.

But the real threat of West Nile virus comes later in summerfrom the Culex tarsalis mosquito, which lays eggs in the spring andneeds to repopulate and find infected birds before it turns itsattention to humans.

That's why the number of human West Nile cases generally peaksin the second week of August and why public policy and personalprecautions often are driven by the less-dangerous nuisancemosquito that shows up earlier.

"Last year, with the dry summer, what we were hearing frompeople is, `There's no mosquito problem, why are you spraying?',and yet the tarsalis, which handles the drier conditions much, muchbetter, was in plentiful numbers," Hildreth said.

South Dakota had 208 human infections and six deaths last year.Twenty-six people have died in South Dakota from West Nile since itfirst appeared in 2002. More than 300 have developed the seriousneuroinvasive complications of encephalitis and meningitis.

The virus already is circulating in some states. Human caseshave been reported in Arizona, Mississippi and Tennessee, said LonKightlinger, epidemiologist in the state Health Department.

South Dakota's per-capita rate of serious complications fromWest Nile is the highest in the nation. Wyoming ranks second,Nebraska third and North Dakota fourth, Kightlinger said.

"For some reason the upper Great Plains is a good home for thatCulex tarsalis mosquito," Kightlinger said.

"We're cooped up all winter here ... and people enjoy theirsummers (outdoors) right at the apex of the West Nile season."

Hildreth and other researchers are trying to piece together howprecipitation and temperature can influence populations of thevirus-carrying mosquito so a town can get the most out its mosquitocontrol efforts by focusing on the virus carriers.

"They have a tough job in that they have to make the (mosquitocontrol) decisions that will affect their community and theyoftentimes have to go against the people's perceptions," Hildrethsaid.

Two years ago, the Culex tarsalis population was down but thepercentage infected with West Nile virus increased.

"So in that particular year we should have seen very few humancases, and yet we saw a surprisingly large number considering howdry things were," Hildreth said. "And I think it's because peopleare just not taking any precautions when it's dry and they'resaying, `There's no problem."'

The state Health Department has $500,000 available this year forlocal mosquito control programs but has changed the distributionformula. Rather than a 50-50 matching grant, towns will receivefunding that takes into account their history of West Nile casesand population.

The department identified 223 entities eligible for funds thatcan be used to buy chemicals or equipment. The money will bedisbursed shortly.

"The way we chose to do it this year -- and this was part of therisk-based approach -- is we wanted to drill down as far as we couldto where the cases where," said Bill Chalcraft, director of publichealth preparedness in the Health Department.

In past years, some counties applied for funds and then handledmosquito control in smaller towns. Those cooperative agreements cancontinue this year if towns agree to pass their funding to thecounty, he said.

"That's one area we've received some questions on. We're nottrying to discourage counties from conducting control operations,"Chalcraft said.

No human vaccine is available for West Nile, so people involvedin outdoor activities need to eliminate standing water that is amosquito breeding ground and protect themselves by using repellant,limiting exposed skin, and avoiding the outdoors when mosquitoesare most active.

West Nile showed up in South Dakota in 2001 with 37 human cases.The virus exploded in 2002 with 1,039 human cases and 14 deaths,leading the state to undertake a late-summer aerial sprayingeffort.

The virus mushroomed in 2002 because people and birds hadn'tbuilt up an immunity and only a handful of communities were doingany mosquito control, Kightlinger said.

"This past summer we resurveyed all those communities with aquickie kind of survey and found 195 were doing some kind ofadultacide (spraying), 155 were doing larvaciding, and 147 weredoing both. We've come from virtually nothing in South Dakota to alot of communities doing a lot of mosquito control," he said.

Seventy-eight applicants shared in $411,819 in initial mosquitocontrol grants last year. The state later distributed $101,000 inemergency larvacide grants to James River Valley towns after recordrainfall in May and another $150,000 to a dozen communities.

(Copyright 2008 by The Associated Press. All Rights Reserved.)