Monitoring the Spread of West Nile Virus, EEE
Common Methods Include Mosquito Control and Monitoring Birds
Aug 19, 2008
For the past decade, West Nile Virus (WNV) and Eastern Equine Encephalitis (EEE) have been a concern among cities and towns throughout the northeastern United States, spurring the implementation of testing operations for mosquitoes and birds.
These monitoring efforts have been combined with more frequent mosquito spraying operations in attempt to control the mosquitoes, which are the primary transmitters of the potentially deadly viruses.
West Nile Virus and Eastern Equine Encephalitis are both blood-borne illnesses, meaning they spread when an uninfected person’s bloodstream is contaminated as the result of direct contact with infected blood. A common mode of transmission involves a bite from an infected mosquito, after the mosquito has bitten a West Nile Virus or Eastern Equine Encephalitis carrier.
The spread of West Nile Virus and Eastern Equine Encephalitis is monitored in three ways: by testing mosquito populations; by testing dead birds (blue jays and crows, specifically); and any cases in humans or other domestic animals are also logged.
WNV, EEE and Mosquito Control
Mosquito control efforts begin in early spring and authorities credit this for slowing the spread of the WNV, which was first discovered in the West Nile region of Uganda in 1937. The West Nile Virus was first found in North America in the summer of 1999. Shortly thereafter, it was discovered that these same mosquitoes were transmitting Eastern Equine Encephalitis.
Mosquitoes are the main mode of transmission for the blood-borne West Nile Virus and Eastern Equine Encephalitis. Therefore, authorities from the mosquito agencies throughout the nation begin each season by using pesticide tablets to treat the water of culverts, ponds and other areas of stagnant water that tend to serve as mosquito nurseries.
Sporadically throughout the summer, mosquito control efforts continue by treating the water directly, and through the utilization of aerosol truck-mounted spraying operations. Throughout the late spring and early summer, mosquito control agencies conduct mosquito spraying operations using truck-mounted sprayers, which target problematic neighborhoods.
Using data from past years and by analyzing the geography of a community, officials determine which areas are most likely to be at-risk of having high mosquito populations, such as those neighborhoods that are located near marshes or areas of wetlands. The spraying operation is then scheduled, announced publicly and in the local newspapers in the days prior to the spraying, which is performed at dusk.
Monitoring Birds and Mosquitoes for WNV and EEE
State public health agencies across the nation team up with mosquito control agencies to perform regular mosquito collection operations using traps. The mosquitoes are then tested for West Nile Virus and/or Eastern Equine Encephalitis.
When a mosquito tests positive, this is significant in that the virus can then be transmitted to a human or animal when a mosquito bite occurs. So to some degree, the locations where positive mosquitoes have been discovered are at greater risk when it comes to the spread of WNV and EEE.
Many states also perform a bird testing program. According to David Henley, Superintendent for the Eastern Middlesex Mosquito Control Project, which oversees the region north of Boston, culex mosquitoes are a primary transmitter of WNV and EEE. Culex mosquitoes tend to target birds. And birds such as robins, blue jays and crows have been found to be especially sensitive to West Nile Virus in particular. So monitoring the bird population and these species in particular provides authorities with a snapshot of the WNV/EEE prevalence.
Notably, it’s up to members of the community to turn in dead birds for West Nile Virus and Eastern Equine Encephalitis testing. If the sample is reasonably fresh, the bird will be accepted by the community’s Health Department and submitted to the State Department of Public Health laboratories for testing.
For additional information concerning West Nile Virus and Eastern Equine Encephalitis, contact your local health department or state department of public health.
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