Mosquito batch in Manchester tests positive for West Nile Virus

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CONCORD, NH – The New Hampshire Department of Health and Human Services (DHHS) has identified the first batch of mosquitoes in 2019 to test positive for West Nile Virus (WNV). The batch was collected in the city of Manchester on August 21, 2019. DHHS is working with the City of Manchester Health Department to notify Manchester residents and those in the surrounding towns of the positive WNV test.

The Manchester Health Department continues its proactive surveillance program, which provides important and timely data that helps determine the risk level of mosquito-borne illness and the appropriate steps to protect the public’s health.

“This is the time of the season that we can expect West Nile Virus to be identified in New Hampshire,” said NH State Epidemiologist Dr. Benjamin Chan. “It is important for residents and visitors to take steps to prevent mosquito bites, as WNV and other arboviruses can be transmitted to humans from the bite of an infected mosquito. From this point in the season until there is a statewide mosquito-killing frost, the risk of infection by mosquito-borne viruses will increase. Use an effective mosquito repellant that contains 30 percent DEET, avoid being outdoors at dawn and dusk, and remove standing water from around the home, where mosquitos reproduce, to limit the risks of catching these infections.”

WNV is an arbovirus transmitted from the bite of an infected mosquito. WNV was first identified in New Hampshire in August of 2000. Symptoms usually appear within a week after being bitten. Symptoms can include flu-like illness including fever, muscle aches, headaches, and fatigue. Many people may not develop any symptoms, or only develop very mild symptoms. A very small percentage of individuals infected with WNV can go on to develop more serious central nervous system disease, including meningitis or encephalitis. If you or someone you know is experiencing flu-like symptoms, including fever and headache, contact your local medical provider.

Prevention guidelines for WNV and other arboviruses can be found below. Anyone with questions about arboviruses, including WNV, can call the New Hampshire Bureau of Infectious Disease Control at 603-271-4496. Fact Sheets on West Nile virus and other arboviruses are available on the DHHS website at For more information, please visit the Centers for Disease Control and Prevention website at

Prevention Guidelines for West Nile Virus and Eastern Equine Encephalitis

  1. Eliminate standing water and other mosquito breeding locations.

In warm weather, mosquitoes can breed in any puddle that lasts more than 4 days!

  • Remove old tires from your property. 
  • Dispose of tin cans, plastic containers, ceramic pots, or other containers. Don’t overlook containers that have become overgrown by aquatic vegetation. 
  • Drill holes in the bottom of recycling containers that are left outside. 
  • Make sure roof gutters are clean and draining properly. 
  • Clean and chlorinate swimming pools and hot tubs. If not in use, keep empty and covered and keep covers free of standing water. 
  • Aerate garden ponds or stock them with fish. 
  • Turn over wheelbarrows and change water in birdbaths at least twice weekly. 
  • Turn over plastic wading pools when not in use. 
  • Remind or help neighbors to eliminate breeding sites on their properties. 
  1. Be aware of where mosquitoes live and breed and keep them from entering your home.
  • Mosquitoes lay their eggs in standing water. Weeds, tall grass, and bushes provide an outdoor home for adult mosquitoes, including several species commonly associated with West Nile virus and eastern equine encephalitis. 
  • Mosquitoes can enter homes through unscreened windows or doors, or broken screens. Make sure that doors and windows have tight-fitting screens. Repair or replace all screens in your home that have tears or holes. 
  • Resting mosquitoes can often be flushed from indoor resting sites by using sweeping motions under beds, behind bedside tables etc. and once in flight, exterminated prior to sleeping at night.
  1. Protect yourself from mosquito bites.
  • If outside during the evening, nighttime, and dawn hours when mosquitoes are most active and likely to bite, children and adults should wear protective clothing such as long pants, long-sleeved shirts, and socks. 
  • Consider the use of an effective insect repellent, such as one containing DEET. A repellent containing 30% or less DEET (N,N-diethyl-methyl-meta-toluamide) for children and adults. Use DEET according to the manufacturer’s directions. Children should not apply DEET to themselves. Repellents that contain Picaridin, para-menthane-diol or oil of lemon eucalyptus have also been determined to be effective.
  • Vitamin B, ultrasonic devices, incense, and bug zappers have not been shown to be effective in preventing mosquito bites. 

For more information on West Nile Virus or Eastern Equine Encephalitis, visit the Eastern Equine Encephalitis and West Nile Virus Website at

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NH Department of Health and Human Services