view 2007 WNV and EEE activity in Massachusetts (MDPH)

view Historical WNV and EEE data in Massachusetts: 2000-2006 (MDPH)

view 2007 WNV Activity in the United States

From spring to late fall, the Massachusetts Department of Public Health monitors West Nile virus and eastern equine encephalitis activity in vulnerable mosquito and animal species. Because these "sentinel" species often contract the viruses well before a human case is identified, the presence of West Nile virus or EEE in these populations helps health officials predict and prevent human infections.

Birds that test positive for the West Nile virus are often the first indication that the disease is present in a community. (Note: Birds are not routinely tested for the EEE virus in Massachusetts because the results do not provide useful information on the level of human risk.

Horses are another sentinel for WNV and EEE because their high exposure to mosquitoes makes them more likely to be infected than people.

Once the virus has been detected in a community, health officials in many states (including Massachusetts) shift their attention to mosquitoes. Unlike monitoring birds or horses, mosquito-based surveillance provides quantifiable information on the potential risk of WNV infection to humans and domestic animals.

Trends

West Nile Virus

West Nile virus was first detected in birds and mosquitoes in Massachusetts in 2000. Since then, the severity of risk posed by the virus initially increased (2001-2002) and then declined throughout the Northeast through 2006.

In 2006 there were no human fatalities from the virus and in 2005 one 80-year old resident of the state died from this illness. Between 2001 and 2006, 71 Massachusetts residents were infected with West Nile virus, including five people who died.

Eastern Equine Encephalitis

Massachusetts has the second largest number of reported human cases of eastern equine encephalitis in the country. Between 1964 and 2005, 242 people in the U.S. were infected with the EEE virus. Of these people, 12% resided in Massachusetts.

Outbreaks of eastern equine encephalitis occur in Massachusetts about every 10 to 20 years. An outbreak typically lasts two to three years. The most recent outbreak of EEE in Massachusetts began in 2004 and included 13 cases with six fatalities through 2006. During this period, infected mosquitoes were detected in Plymouth, Bristol, Middlesex, Worcester, Norfolk, and Essex counties.