Add the deadly eastern
equine encephalitis (EEE) virus to the list things we might find more of in our
climate-changed future.
As mosquito testing
for EEE gets underway this month in Massachusetts and Rhode Island, a
recent report from the New England Journal of Medicine draws
a potential link between climate change and a 10-year upswing in the number of
infections as well as the northward expansion of the virus.
If warmer winters, hotter summers, and more drought and precipitation are likely, so is EEE. The article by Philip M. Armstrong and Theodore G. Andreadis says rainfall and accumulated groundwater increase the habitats for mosquito larvae growth. Warmer winters may help infected insects survive longer and facilitate the migration to once-cooler regions. Warmer summers speed up the development and breeding of infected mosquitoes, which also increases their number and range.
A spike in EEE
infections shows that the virus might already be spreading. Between 1991 and
2002, eight cases of EEE were reported in the Northeast. By contrast, 42 cased
were report between 2003 and 2012.
Cases were mostly
confined to mid- and lower New England, until 2004 when New Hampshire had its
first human case of EEE, followed by seven cases and two deaths in 2005. Last
September, Vermont reported its first human cases of EEE, which killed two men,
ages 89 and 49. After documenting about one case a year from 1990 to 2003,
Massachusetts reported 20 human infections between 2004 and 2012. Six of the
cases were new to areas such as central Massachusetts and the North Shore,
including two people who died from EEE last year.
History of EEE
Armstrong and
Andreadis also examine the long-term patterns of EEE. The virus was discovered
in the United States in 1933. The first human cases occurred in 1938, when an
outbreak in southeastern Massachusetts resulted in 34 EEE infections and 25
deaths. In 1959, another epidemic hit New Jersey, resulting in 32 cases and an
equally high mortality rate. Since then, limited outbreaks had occurred in
Massachusetts and southern New Jersey. A small number of cases were reported in
central New York and Rhode Island.
Although overall cases
of EEE have increased, the outbreaks are intermittent and influenced by
weather, according to the report's authors. Infections are still considered
rare, as each summer the virus makes a complicated jump from mosquitoes to
songbirds living in freshwater swamps. The virus is then transmitted back from
birds to mosquitoes that infect humans and other mammals. Although mosquito
infections occur in early summer, it may take a month before human cases
appear. The infection season typically ends with the first frost.
Armstrong and
Andreadis suspect the increase of human cases is attributed to wetlands restoration,
suburban development and population growth near EEE habitats. But weather, they
say, is likely the most dominant cause. Above-average rainfall, mild winters
and EEE activity during the previous year are the biggest factors for giving
stamina to the virus.
The New Hampshire and
Vermont cases are part of the 10-year increase in EEE infections in humans in
new regions while infections are increasing in the usual regions.
“We are now seeing
recurrent EEE cases each year and their expansion into northern New England for
the first time, a phenomenon that requires further scrutiny,” according to the
report.
Climate change may
also make the Northeast more hospitable to other rare mosquito borne diseases
such as malaria and dengue, according to Armstrong and Andreadis.
EEE is the most deadly
mosquito-borne disease in North America, with a survival rate of about 50
percent. Half of survivors suffer severe neurological impairment. Long-term
care costs an estimated $3 million per patient during their lifetime. Symptoms
begin three to 15 days after a bite from an infected mosquito. Symptoms include
fever, headache, nausea, rash, stiff neck, muscle weakness and
disorientation.
There is no vaccine
and or treatment for EEE. Targeted spraying with trucks is most common in
Massachusetts after multiple detections of EEE. Aerial spraying is typically
employed after EEE appears in clusters of communities. The pesticide
combination of sumithrin and prallethrin is the most popular treatment.
Last year, 21
communities in Bristol and Plymouth counties of Massachusetts received aerial
spraying. Environmental groups such as the Northeast Organic Farming
Association oppose such pesticide treatment.
Due to its heavy
proportion of wooded swamps, southeastern Massachusetts is typically one of the
first regions to detect EEE-infected mosquitoes. In 2006, a 58-year-old Everett
woman and a 9-year-old Middleboro boy died from EEE. Another person died in
2008 and a Raynham man died in 2011.
Armstrong and
Andreadis note that the reasons for the increase in cases and northern
expansion aren’t verified. But the changing climate, so far, seems to show the
EEE has found a hospitable environment.
Outdoor testing for
EEE begins this week in Rhode Island and will continue through September.
Massachusetts begins testing June 17.