West Nile Virus-Positive Mosquito Pool in 2009 Confirmed in Maryland

The Maryland Department of Agriculture (MDA) announces the first state detection of a West Nile virus (WNV) mosquito pool in Maryland in 2009. State Department of Health and Mental Hygiene (DHMH) laboratory results confirmed the presence of WNV in mosquitoes (Culex pipiens) collected on July 21 in the Pocomoke City, Worcester County. MDA mosquito control personnel are continuiong to work aggressively to reduce mosquito populations across the state, including aerial spray operations on the Eastern Shore.

"Because of spring rains in much of the state, mosquito populations are high and we know that West Nile virus may be present throughout Maryland. It typically appears at this time in the summer, so we are not surprised with this positive finding," says Secretary of Agriculture Buddy Hance. "The confirmation of virus-positive mosquitoes serves as a reminder to all residents to continue protecting themselves against mosquito bites and to conduct backyard mosquito control activities in addition to MDA's routine surveillance and spray activities."

The MDA mosquito control office, in cooperation with DHMH, is conducting state-wide surveillance activities to monitor mosquito populations and detect mosquito-borne viruses of public health concern. Surveillance activities for adult mosquitoes use traps and landing rate counts. Mosquito control activities conducted by MDA include larviciding and spray programs for adult mosquitoes in communities that voluntarily participate in the agency's program. Additional mosquito-borne disease surveillance is conducted by the U.S. Department of Defense on military installations in Maryland.

"Mosquito control remains especially important to decreasing the risk of infection with all mosquito borne diseases," said Michael Cantwell, MDA chief of mosquito control. "MDA is taking appropriate steps for mosquito surveillance and mosquito control activities in participating Maryland jurisdictions through the end of September."

Most mosquitoes do not pose a threat to public health because they are not infected with viruses or other pathogens. Less than one percent of people bitten by a mosquito carrying West Nile virus will become ill. People most at risk for developing symptoms of the disease are those over 50 and those with already compromised immune systems; however, all residents should continue to take measures to protect themselves from mosquito bites. These measures include:

  • Avoid unnecessary outdoor activities at dawn and dusk when mosquitoes are most active;
  • Wear insect repellents, according to product labels, especially if you will be outside between the hours of dusk and dawn when mosquitoes are most active.
  • Wear long sleeves and long pants to help avoid mosquito bites. Avoid mosquito infested areas.
  • Install and inspect window and door screens in homes and stables and repair any holes found.
  • Remove standing water from flower pots, tarps, trash receptacles, and other containers;
  • Vaccinate horses, mules, donkeys and ratites according to your veterinarian's advice.
  • Flush pet food and water bowls and bird baths regularly; and,
  • Remove unnecessary water-holding containers.

There is neither a specific treatment nor a vaccine against WNV for humans. There are, however, effective vaccines against the virus for horses, ostriches, and emus--also known as ratites. Owners are encouraged to get their animals vaccinated and boostered in a timely manner in consultation with their veterinarian.

For additional information about MDA's mosquito control program, please call 410/841-5870 or visit www.mda.state.md.us.

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