Published on September 12, 2016

The buzz about West Nile and other mosquito-borne viruses

The buzz about West Nile and other mosquito-borne viruses

It’s been a summer for mosquitoes in the news.

By mid-August, West Nile virus had been found in mosquitoes trapped in Falmouth and Marstons Mills, and a mosquito carrying Eastern equine encephalitis had been caught in Yarmouth, according to the Cape Cod Times. And, all this happened as the battle against Zika, another mosquito-borne virus, plays out around the world.

Kumara Sidhartha, MD, MPH, medical director at Emerald Physicians, took a simple action to allay patients’ fears: He created and distributed a fact sheet about mosquito-borne illness in the Emerald offices. The message: Understand the risks, protect yourself and do what you can to help prevent mosquitoes from becoming a public health hazard in the community.

“Sometimes the perception of risk by the public can be something that is not matching the real risk,” Dr. Sidhartha said. “That just requires more education to understand what the risk really is.”

Dr. Sidhartha and Gabrielle Sakolsky, entomologist and assistant superintendent with the Cape Cod Mosquito Control Project, the local outpost of the state’s monitoring efforts, recently discussed the risks of mosquito-borne illnesses and what actions you can take.  The Massachusetts Executive Office of Health and Human Services also has extensive resources about mosquitoes, insect repellents and bite prevention on its website.

  1. Understand the risks.

Eastern equine encephalitis is a serious disease that occurs sporadically in the state, according to the Massachusetts Department of Public Health. There were no cases in Massachusetts in 2014 or 2015, and not a single human case has ever been found on Cape Cod, according to Sakolsky. The disease has a 30 to 50 percent mortality rate and can cause life-long neurological damage in survivors. There is no vaccine.

According to Dr. Sidhartha, symptoms of EEE include:

  • An abrupt fever of over 101 degrees
  • Headache
  • Severe body aches
  • Vomiting and/or diarrhea
  • A change in mental state within two to 10 days of a mosquito bite

“The big clue is in the mental status – if the person is becoming unusually drowsy or sleepy or has more than normal agitation, and all that is happening in an abrupt manner in the presence of a mosquito bite,” he said.

Those most at risk, as with all viruses, are children, the elderly and those with chronic medical condition,he said.  If these symptoms develop within two weeks of a mosquito bite, he recommends calling your doctor.

Only four EEE-bearing mosquitoes have been found on the Cape since testing began in 1972, said Sakolsky, who sends samples to the state during the mosquito season. “I was very surprised,” she said about the recent finding in Yarmouth. “I send them in almost every week expecting them to be negative.”

Traditionally, the Cape has been outside the parameters for EEE since the mosquitoes that carry it like to breed in pools created by tree roots in swamps more common in Bristol and Plymouth counties, she said. And even odder, the one found carrying it in Yarmouth was a Culex mosquito, a type that prefers drier weather and is more likely to carry West Nile. Because it tends to be dryer, the Cape is home to only about 25 common species of mosquitoes, she said, as compared to more than 50 in the rest of the state.

West Nile first appeared in the United States in 1999 and is carried by birds, then spread by mosquitoes. The majority of people infected will have no symptoms at all and less than 1 percent will develop serious symptoms. In Massachusetts, there were at least nine fatal cases between 2002 and 2015 and all were people over 60, according to the DPH. As of Aug. 30, the state had one case this summer, according to the  U.S. Centers for Disease Control. She was a woman in her 70s from Middlesex County, according to the DPH.

  1. Protect yourself.

The best protection against mosquito-borne illness is to avoid being bitten. The old standbys still apply, according to experts like Dr. Sidhartha and Sakolsky.

  • Wear long pants and long sleeves.
  • Use insect repellent. Look for a repellent that says on the label that it is approved by the U.S. Environmental Protection Agency, said Sakolsky. That includes those containing DEET (N, N-diethyl-m-toluamide) or other chemicals, as well as so called “natural” repellents such as lemon eucalyptus oil. Just be sure to pay attention to the warnings on the label about sensitivities and appropriateness for children. The DPH has detailed information about repellent ingredients and how to apply repellent on its website.
  • Avoid outdoor activity from dusk to dawn when mosquitoes are their most active. Rest assured that in Massachusetts, the season will come to an end in a few weeks. The mosquito risk is greatly reduced once the temperature drops below 50 for more than three hours at a time, said Dr. Sidhartha.
  • Keep your window and door screens in good repair.
  1. Help protect the community. Mosquitoes breed in standing water and the Culex species in particular, Sakolsky said, seeks out manmade water traps like watering cans, clogged drains, swimming pool covers and the inside of old tires. Even though it’s been a dry summer, run-off from lawn watering systems and sprinklers runs into catch basins, another favorite breeding ground. Do what you can to avoid pools of water around your yard. Change the water in birdbaths at least once a month.

The discovery of EEE in Yarmouth is disconcerting, but it doesn’t change the public health message, said Dr. Sidhartha.

“Just continue the regular precautions for mosquito bites that we already have in place. Even though it’s a new finding, the risk is relatively low and we just need to be aware of prevention and be aware of the very, very rare possibility of a human case, which has never happened on the Cape.”