West Nile Virus Risk Levels in Massachusetts
From the Public Health Director 08/30/18
Important Information regarding West Nile Virus and Protecting Yourself from Mosquito Bites
In early August and also today, “Culex” species mosquitoes collected from South Wayland tested positive for West Nile Virus. We were recently informed by MDPH that they are seeing many mosquitoes testing positive for WNV in Massachusetts and as a result they have raised the risk level in the entire state to “moderate” risk for WNV. Also, 4 humans have been diagnosed with West Nile Virus, all connected with the greater Boston Area which has now been raised to a “high” risk level for WNV. We will continue to monitor the situation and any new information we receive from the Mass Department of Public Health (MDPH). Most importantly, we would like people to be aware of this information and we strongly encourage people to use precautions for protection against mosquito bites when engaging in outdoor activities. Especially people over 50 and those who are immunocompromised who are more likely to develop WNV disease. We also advise people to check your yards for items that can collect water and harbor mosquito breeding. As outlined further below in this memo we have provided recommendations for avoiding mosquito bites and how to prevent your yard from becoming a mosquito breeding area.
Catch basins have been treated for mosquitoes
The catch basins in town have been treated with ALTOSID XR Briquettes supplied by the Wayland Board of Health and distributed by the East Middlesex Mosquito Control Project. This treatment is done every year to control mosquito larvae to reduce mosquito-borne illness. Altosid is a larvicide in a briquette form that disrupts the normal growth pattern of immature mosquitoes in water and prevents them from becoming breeding, biting adults. ALTOSID is a long-term (up to 150 days), cost-effective and environmentally responsible mosquito control larvicide.
The treated catch basins have been marked with a white dot. The Town of Wayland contracts the services of the East Middlesex Mosquito Control Project for mosquito control including helicopter spraying using BTI larvicide in the spring and catch basin treatments in the early summer. Our program during mosquito season also includes mosquito trapping, identifying populations and surveillance for diseases and species.
Mosquito habitats in Wayland and why treating catch basins is important
The “Culex” mosquito species is common in suburban communities such as Wayland. This mosquito species prefers to breed/lay eggs in small artificial containers such as birdbaths, old tires, buckets, clogged gutters, and other standing water sources which can be found in people’s backyards and other similar areas of the suburbs (including catch basins).
Culex mosquitoes are the primary vectors of West Nile Virus. West Nile Virus (WNV) is a mosquito-carried virus that can cause illness in people ranging from a mild fever to more serious disease like encephalitis or meningitis. WNV is most commonly spread to people through the bite of an infected mosquito. The Culex species are also known as “bridge” vectors that will feed on birds and people. As the summer continues to progress, birds could be infected with West Nile Virus and the virus could be transmitted to a human when a mosquito bites a bird carrying the WNV virus and then subsequently bites a person.
The catch basin treatments using Altosid will reduce the population of Culex mosquito larvae that could be growing in catch basins (standing water environment), decreasing the risk of West Nile Virus infection in humans.
To prevent a yard from becoming a source for Culex mosquitoes and potentially invasive mosquito species, homeowners should make a thorough inspection of their property and remove, empty, cover or treat water-holding containers. During the summer, mosquito larvae can complete their development in water within a week.
What to do in your yard to prevent mosquito breeding, West Nile Virus (WNV) and other Arboviral Diseases:
- Mosquito proof your home and drain standing water in your yard
- Containers where mosquitoes commonly lay eggs include neglected swimming pools, water in loose-fitting pool covers or tarps, unscreened rain barrels, rimless tires, and plastic toys, flower pots, trash barrels/containers. Check rain gutters, including all fittings and drains.
- Tires should be disposed of properly or stored inside.
- Rubbish barrels, wheelbarrows and small boats should be covered or stored upside down.
- The water in wading pools and birdbaths should be changed weekly.
- Infrequently used pools should be covered or properly maintained.
- Some mosquitoes like to come indoors. Keep them outside by having tightly-fitting screens on all of your windows and doors. Fix any holes in screens and screen doors and replace worn weather stripping.
- Keep the grass in your yard cut short and shrubs trimmed.
- Once a week empty and scrub, turn over, cover or throw out any items that hold water.
- Rainwater collection barrels tips:
- Always use a mosquito-proof screen to seal and cover the rain barrel or other water-saving container. Mosquito-proof screen is a very fine mesh, usually 1/16 of an inch. If the barrel is covered, this will reduce the likelihood of mosquitoes becoming a problem.
- If the barrel is holding a lot of water consider mosquitofish, or consider treating with products containing Bti (always read the product label and use according to the instructions).
- Keep the rain barrel lid and connectors sealed to help keep bugs out.
- Be sure to always remove the water that pools at the top of the barrel at least once or twice a week.
- If possible, place your barrel on a surface that will soak up any water that overflows so it doesn’t pool and create a mosquito habitat.
- Regularly inspect your rain barrel system. Check for cracks or leaks. Be sure that all fittings and seals are intact and that no water accumulates on the ground around the barrel.
- Clean the barrel on a regular basis. Drain it completely and clean it out at least twice a year.
What you should do to avoid mosquito bites
At this time of year mosquito populations are on the rise and residents should take precautions to avoid mosquito bites.
Be aware of peak mosquito hours:
- The hours from dusk to dawn are peak biting times for many mosquitoes. Mosquitoes are more active in damp, shady areas, during cloudy humid days, and at night. Consider rescheduling outdoor activities that occur during evening or early morning. Also, take extra care to use repellent and protective clothing.
- There are some emerging mosquito species that are out and active during the day. Be sure to protect yourself and family members during the day also.
Wear protective clothing:
- Clothing can help reduce mosquito bites. Although it may be difficult to do when it’s hot, wearing long-sleeves, long pants and socks when outdoors will help keep mosquitoes away from your skin.
- Cover up the arms and legs of children playing outdoors. Baby carriages and playpens should be covered with mosquito netting.
Apply insect repellent when you go outdoors.
- Use a repellent with DEET (N, N-diethyl-m-toluamide), permethrin, picaridin (KBR 3023), IR3535 (3-[N-butyl-N-acetyl]-aminopropionic acid) or oil of lemon eucalyptus [p-menthane 3, 8-diol (PMD)].
- DEET products should not be used on infants under two months of age and should be used in concentration of 30% or less on older children.
- The Center for Disease Control has has recently listed Oil of lemon eucalyptus as providing protection against mosquitoes, however, it should not be used on children under three years of age.
- Permethrin products are intended for use on items such as clothing, shoes, bed nets and camping gear and should not be applied to the skin.
- Protect pets and horses from mosquito bites.
- Always follow the instructions on the label of any repellent. More information on choosing and using repellents safely is listed below.
For further information on WNV or EEE, log unto the Massachusetts Department of Public Health web site at:
If residents have any questions about mosquitoes or how to control them: the East Middlesex Mosquito Control Project can be reached at:
Choosing and using repellents safely:
The National Pesticide Information Center (NPIC) toll free at 1-800-858-7378 or online at http://npic.orst.edu/index.html. If you can’t go online contact MDPH at (617)983-6800 for a hard copy of the fact sheet.
MDPH 2017 Arbovirus Surveillance and Response Plan
MDPH Mosquito-borne Diseases
Julia Junghanns, R.S., C.H.O.
Director of Public Health