Plymouth County Mosquito Control Project

 

Introduction: Eastern Equine Encephalitis (EEE) is a rare form of viral encephalitis that is transmitted by mosquitoes. (The word encephalitis is a medical term for swelling of the brain.).   EEEV found along the Atlantic and Gulf coasts of the U.S. as well as Michigan, Ohio and upstate New York. With the most human cases occurring in Florida, Georgia, Massachusetts and New Jersey.  Eastern Equine Encephalitis is one of the most deadly mosquito borne diseases in the United States.  The CDC reports that about 35% of the people who contract the disease will die and of the survivors 35% will have long term neurological deficits.  People at greatest risk for developing EEE are people under the age of 15 or over the age of 50.

While EEEV has undoubtedly been in Massachusetts for a long time, the virus was first recognized in the state in 1938. Between 1938 and 2005 there have been 83 human cases in Massachusetts, 47 of them died. The majority of human cases in Massachusetts have occurred in Norfolk and Plymouth counties.  In 2005 there were 4 human cases reported in Massachusetts all of the cases occurred in Plymouth County.  


Transmission Cycle: The transmission cycle of EEEV is complex, and involves several different mosquito species. The mosquito Culiseta melanura transmits EEEV to our wild birds. The birds in turn infect more mosquitoes. The virus may leave the Culiseta melanura-bird cycle through the infection of additional mosquito species. When these other mosquito species become involved mammals, including people, are in danger of infection. While the risk of infection is usually very low, human cases may occur from late July to October.

EEEV State Wide Program: The state of Massachusetts has a EEEV monitoring and control program that is designed to assess the level of risk and dictate appropriate action for both health agencies and the general public. Every summer the Massachusetts Department of Public Health (DPH) sets out mosquito traps in areas that have historically had EEEV activity. In recent years Plymouth County Mosquito Control Project has also set traps that are designed to supplement the trapping DPH has been doing.  Mosquitoes are collected from these traps every week and tested for EEEV. When the virus is isolated from mosquitoes, DPH notifies mosquito control districts and local boards of health and issues a press release to the public. This press release contains information describing personal protection measures and proper use of mosquito repellents. DPH also issues recommendations to state mosquito control officials based on the estimated level of risk to humans. It is the policy of Plymouth County Mosquito Control Project to take special action against EEEV only if the DPH has recommended it.


EEEV in Plymouth County: Since 1938, Plymouth County has had 33 human EEEV cases. This is the highest number of human cases for any county in Massachusetts. Plymouth County Mosquito Control Project expends considerable effort to identify areas that produce the mosquitoes likely to be vectors of EEEV to people. While some of these areas are targeted in an effort to reduce nuisance populations, mosquito control focuses on reducing EEEV transmission only if the DPH has recommended it.


Protecting Yourself and Your Family: Unfortunately, there is no commercially available vaccination for people. The best way to protect yourself is to prevent mosquito bites. The Public Health Department makes the following recommendations:

1. If you must be outdoors at dawn and dusk when mosquitoes are most active, wear long-sleeved shirts and long pants. Use mosquito repellent that contains DEET, permethrin, or  picaridin.  Please see Repellents for more information.   

2. Take special care to cover up the arms and legs of children playing outdoors near swampy areas. When you bring a baby outdoors, cover the baby's carriage or playpen with mosquito netting.

3. Fix any holes in your screens and make sure they are tightly attached to all your doors and windows.

4. Mosquitoes can breed in water that collects in ditches, clogged gutters, old tires, wheelbarrows, and wading pools. Don't let stagnant water collect around your home. (information taken from Public Health EEEV fact sheet)

EEEV and Horses: EEEV is a very serious disease for horses. Horse mortality ranges from 80-90% of the horses infected. Symptoms include unsteadiness, erratic behavior, loss of coordination and seizures. There is no cure for the disease and death usually occurs within 48-72 hours after onset of the first symptoms.  Infected horses cannot pass the virus to humans through contact, body fluids or any other physical mechanism. Also, a sick horse cannot infect additional mosquitoes because it does not circulate sufficient amounts of virus in the blood. Transmission between horses is not possible.  The only way to prevent a horse from contracting EEEV is through a vaccination. A veterinarian should administer the vaccination each year. Please check with your veterinarian for additional information on the vaccine.

Links to more EEEV information:

Eastern Equine Encephalitis and Horses - New Jersey Mosquito Control

Massachusetts Department of Public Health Eastern Equine Encephalitis Fact Sheet

 

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