Environmental clues sought for West Nile

SIOUX FALLS — The challenge of trying to predict human risk of West Nile virus each summer will have researchers studying satellite images of South Dakota and Ethiopia.

This ecological forecasting will look for clues in how precipitation, vegetation and temperature might influence mosquito populations and the resulting spread of West Nile Virus in the Northern Plains and malaria in the highlands of Ethiopia.

“The basic idea is that if we can understand something about the environmental relationships, the environmental drivers that are influencing the mosquitoes, the virus, the birds — that is going to allow us to do some sort of forecasting of the particular times and places where the risk of disease transmission is going to be the highest,” said Mike Wimberly, an associate professor at South Dakota State University and the principal investigator.

The four-year study is funded with a grant of just over $1 million from the National Institutes of Health.

Mosquitoes transmit West Nile from infected birds to humans. In Ethiopia, the insects transmit malaria among humans.

Key to the research will be weekly satellite images collected and processed at the Earth Resources Observation and Science Center near Garretson and interpreted by Gabriel Senay, a remote sensing hydrologist.

“We can see what’s happening with the vegetation and that, in effect, serves as a recorder of what’s going on in terms of the temperature and the moisture on the earth’s surface,” said Wimberly.

Researchers will use those readings to look for correlation with spikes in reported cases of malaria or West Nile.

West Nile has killed 26 people and sickened 1,716 since it was first discovered in South Dakota in 2002. The 39 human cases last year with no deaths was the lowest summer total since 2002.

Lon Kightlinger, epidemiologist in the South Dakota Health Department, said people are doing a better job protecting themselves from mosquitoes by using repellent, wearing appropriate clothing and avoiding the outdoors when virus-carrying mosquitoes are most likely to be active.

“Many more cities now have mosquito control programs, so that’s a plus in our direction. We’re waging those battles, plus the human population has become more immune,” he said.

Humans bitten by an infected mosquito are thought to develop lifelong immunity.

Kightlinger said 80 percent of people bitten by an infected mosquito show no symptoms of West Nile virus. Others may develop a mild illness with fever, headache and body aches. Extreme cases can result in inflammation of the brain or spinal cord lining, or death.

Only certain species of mosquitoes carry the virus. Their population peaks in mid-July, leading to a peak in human cases in mid-August. The state’s worst outbreak was in 2003 when there were 14 deaths and 1,039 human infections.

The following year, the Health Department started a grant program to help local governments control mosquitoes.

State funding for control programs dropped substantially this year because federal money dried up and state government as a whole curtailed spending. The total of annual grants had ranged from $411,819 to $908,082 in each of the past five years, but is only $200,000 this year — all in the form of chemicals given to local programs.

“This was the best we could do,” said Tom Martinec, director of the Division of Health Systems, Development and Regulation within the Health Department.

The state provided an average of $1,100 worth of chemicals to 177 city, county and tribal programs.

“For the bigger (control) programs it’s certainly not going to be near enough for what they will need,” Martinec said. “For some of the smaller programs, that will get them though a good part of the summer.”

Martinec said the grant program was never designed to be ongoing but was meant to help local governments buy equipment and cover their upfront costs to get a mosquito spraying or larvaciding program in place.

Wimberly said investigators will spend about two years compiling data, doing research and developing some forecasting tools. Then they’ll shift to making forecasts, validating them and getting response from public health officials on how useful the forecasts are.

“We’re not going to be able to point to a very precise location and say in this week people are going to get West Nile here,” he said. “We know we can predict something, but at what scale, how much and how useful is it?”

“It may turn out to be very useful just to be able to say we can tell you with a fairly high certainty that in this year things are going to be bad in eastern South Dakota but not so much in western South Dakota, or it looks like a hot year is coming up for North Dakota but maybe it won’t be so bad in the south.”

Tags: west nile, news