Rain revives mosquito population

On the Farm

West Nile scare spurs stepped-up control program

September 02, 2007|By Ted Shelsby

The Maryland Department of Agriculture is boosting its mosquito control efforts in the wake of what health officials fear could be the first human case of West Nile virus in the state this year.

Agriculture officials have more than doubled mosquito trapping on the Lower Eastern Shore, said Cy Lesser, the department's chief of mosquito control.

The move followed a report last week by the state Department of Health and Mental Hygiene on what it suspects is a human case of the virus. Officials declined to say much about the case except that it involves a resident of Worcester County.

"The report has not been confirmed," said Karen Black, a health department spokeswoman. "That will take a couple of weeks."

For most of the year, the mosquito population had been well below average because of the drought, Lesser said. That changed a few weeks ago when a combination of rain and a new moon increased tidal flooding of several hundred thousand acres of Eastern Shore marshland.

No predators

The water revived the mosquito eggs that had lain scattered on the marshland mud for weeks, and they rapidly developed into adult mosquitoes. The drought had eliminated the minnows that usually feed on the mosquito larvae.

"There were no predators around to control the mosquito population," Lesser said.

The worst could lie ahead. September traditionally has heavy mosquito activity, he said.

"There is increased potential of mosquitoes carrying the virus," Lesser said. "We don't think people need to be unduly concerned, but they should take some efforts to reduce the threat."

Mosquito control is the key tool in the effort to ameliorate the risk of infection with all mosquito-borne diseases, said Maryland Agriculture Secretary Roger L. Richardson.

The department is intensifying its efforts with additional surveillance and more aggressive control activities on the Lower Eastern Shore for the rest of the mosquito season. Steps include increased flights by the twin-engine Beechcraft King used to spray mosquito-killing chemicals.

More than 50,000 acres were sprayed last week, and more spraying will take place this week, Lesser said.

The department also is using trucks to spray areas that can be reached from the road, and field workers have been meeting with residents to suggest ways to rid their yards of containers holding water and other areas where mosquitoes can breed.

Since 2001, there have been 136 cases of West Nile virus in Maryland and 18 deaths, health officials said. Six cases were reported last year, one more than in 2005. The disease peaked in the state in 2003, when 73 cases resulted in eight fatalities.

Health department officials said most mosquitoes do not pose a threat to public health because they are not infected with viruses or other pathogens. Also, fewer than 1 percent of the people bitten by mosquitoes carrying the West Nile virus become ill.

People older than 50 and those with compromised immune systems are at most risk for developing symptoms of the disease.

Common symptoms

The most common symptoms are fever, headaches, weakness and joint and muscle pain.

The state agencies suggest several steps that residents can take to protect themselves:

Avoid unnecessary outdoor activities at dawn and dusk, when mosquitoes are most active.

Wear light clothing, long pants, long-sleeved shirts and hats when outdoors.

Use mosquito repellents. The Department of Agriculture says that those containing DEET or Picaridin work better and last longer.

Remove standing water from flowerpots, tarps, receptacles and other containers.

Flush pets' food and water bowls and birdbaths regularly.

There is no vaccine against the West Nile virus for humans.

Vaccines are available for horses and some other farm animals. More than 230 horses were infected with the virus in 2003, but no cases were reported last year.

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