Mosquito Surveillance & Control: The Importance of Prevention

The New Hampshire Department of Health and Human Services reports that 18 mosquito pools tested positive for West Nile Virus last week.  This has led to the recommendation that a public health threat be declared for the state.

The positive results were found in different cities and towns throughout the state and up significantly from 2011. According to Amherst’s newly appointed Health Officer Dr. Katherine Lockwood, "I am not surprised by the increased positive findings in New Hampshire this year” adding that the potential does exist for more mosquito-borne virus positive finding to appear in additional New Hampshire communities before the 2012 season ends in late October.

"Most people bitten by an infected mosquito don't get sick. Those people who do get sick usually have a mild flu-like illness; but in some more severe cases, people suffer from encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord)," Dr. Lockwood said. "The elderly and children in the community are at highest risk of suffering a serious illness or death from the disease." According to the NH Department of Health and Human Services risk level assessment map, available at www.dhhs.state.nh.us, Amherst is presently right on the border of communities such as Nashua, Bedford and Merrimack whose current risk level category is HIGH.

"The key to preventing the spread of West Nile virus and EEE is to control the mosquito population," said Lockwood. Controlling the mosquitoes can involve three primary activities: educating the public on eliminating mosquito breeding areas around homes, eliminating or treating standing water on property and larvaciding to prevent the development of adult mosquitoes. "Spraying adult mosquitoes should only be used as a last resort. A pro-active program to eliminate areas where mosquitoes breed in Amherst may significantly reduce the possibility of mosquito-borne illnesses and the need for emergency spraying down the road."

Public health officials recommend a four pronged approach to dealing with these disease threats.

• Establish a local or regional mosquito surveillance program.
• Eliminate or treat now any mosquito breeding sites.
• Develop systems for responding to citizen concerns of mosquitoes or standing water.
• Educate citizens on West Nile virus and how to eliminate mosquito breeding areas. 

"Mosquitoes can breed in very small amounts of water that is stagnant for more than five days," Lockwood said. "Some kinds of mosquitoes breed in containers such as buckets, potted plant trays and garbage cans and can breed in water that collects in trash, such as old tires, tin cans, styrofoam cups and yogurt cups. Some prefer to breed in marshes, flood plains, backed-up ditches, mud puddles and small ponds less than a foot deep with emerging vegetation." Bodies of water that are usually not a concern for breeding mosquitoes include permanent ponds, streams, moving bodies of water or any water with existing fish populations.

"The two most useful methods for mosquito surveillance are traps for adult mosquitoes and dip sampling for larval mosquitoes. Adult mosquitoes are usually trapped using battery-powered light traps baited with CO2," Lockwood said. "The traps are generally set up on a regular schedule at designated areas, but may be moved around to investigate potential problem areas. Once a local mosquito species is identified, you can usually determine the source of the mosquito based on its breeding and flight habits."

In addition to a contracted professional mosquito surveillance and response plan, public education is an important tool in combating West Nile virus and EEE, because the types of mosquitoes most likely to carry it are those that breed in containers found around the home. “A big part of the battle to control mosquitoes lies with community residents” Lockwood said.

"Citizens need to know how to prevent mosquitoes from breeding in their yards by turning over or removing containers that collect rainwater such as old tires, potted plant trays, boats, buckets and toys. Birdbaths and wading pools should be cleaned once a week," Lockwood said. "Roof gutters and downspout screens should be cleaned regularly and standing water should be eliminated on flat roofs."

"We also want to encourage the public to properly protect themselves from mosquitoes when they are outside by wearing long, loose and light colored clothing. They should follow label instructions when using insect repellent. The repellents for adults should contain no more than 20 to 30 percent DEET and less than 10 percent for children," Lockwood said.

For more information in understanding the State of New Hampshire Public Health Services “Arboviral Illness, Surveillance, Prevention and Response Plan” please visit: http://www.dhhs.state.nh.us/DHHS/CDCS/LIBRARY/Policy-Guideline/arboviral-response-plan.htm