Sustaining EEE-Environmental Conditions
March 21, 2010

As it turns out, weather and climate affect the transmission cycle of Eastern Equine Encephalitis (EEE). There must be specific environmental conditions present to sustain the disease and, as these conditions are present, we notice that cases of EEE spike.

The weather and climate of New Hampshire is some of the most dynamic in the world (Keim, 2004). In a calendar year, temperatures range from sub-zero to near triple digits. Precipitation in the form of snowfall and rainfall also occur in varying amounts across the state. Land elevation also plays a role in both temperature and precipitation as higher elevations experience lower temps and windward areas greater amounts of precipitation (Rainshadow Effect). Despite elevation, summers in New Hampshire are not unlike those in Miami or Atlanta as the warm, humid air mass can extend from southern Florida to New England. However, this is not the case during the winter as the polar front from Canada doesn’t normally extend too far down the east coast. (Keim, 2004).

Environmental factors conducive to EEE have the ability to linger across multiple seasons in New Hampshire. Mosquitoes that transmit EEE can survive in temperatures between 55.4-95 degrees Fahrenheit, but need significant rainfall to promote their longevity and provide habitat (Sellers, 1980; Thompson and Connor, 2001). In New Hampshire, these conditions can last from late spring to early fall (May-September).

Research by the Centers for Disease Control have noted that EEE is transmitted most commonly adjacent to freshwater hardwood swamps. Some research has noted that vegetation, such as the Papyrus Plant, has contributed to lower mosquito densities, specifically in swamps in highland Africa (McCrae, 1983). (Of course, the Papyrus research was done to support ways to combat Malaria. But both Malaria and EEE have striking similarities-both vector-borne diseases-and since Malaria research has been evolving for an extended timeframe, it is only the progression of science to compare both diseases and use methods which have worked in the fight against Malaria for the fight against EEE). EEE vectors are also known to originate in tall grass, wooded areas, and man-made items such as old tires and gutters.

As urbanization has spread in rural areas of New Hampshire there is growing concern of increased EEE incidence. As humans spread into natural vector habitats there must be a new plan to prevent EEE. Current methods of deterring EEE cannot be exclusively depended upon.

Keim, B. 2004. A Climate Primer for New England, Airmap.  Retrieved from: http://airmap.unh.edu/background/ClimatePrimer.

McCrae, A.W.R. 1983. Oviposition by African Malaria Vector Mosquitoes. I. Temporal Activity Patterns of Caged, Wild-Caught, Freshwater Anopheles gambiae Giles Sensu Lato.  Annals of Tropical Medicine and Hygiene, 77: 615-625.

Sellers, R.F. 1980. Weather, Host and Vector: Their Interplay in the Spread of Insect-Borne Animal Virus Diseases.  The Journal of Hygiene, Vol.85, No.1, pp.65-102.

Thompson, M.C., and Connor, S.J. 2001. A Framework for Research in Africa: Malaria Early Warning Systems.  Roll Back Malaria Cabinet Project, World Health Organization.

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