The ultimate guide to Boston bug battling
Boston listed as high risk for West Nile virus by the Massachusetts Department of Public Health
Though returning to campus may feel like the end of summer, Massachusetts mosquito season lasts long beyond the end of MIT’s summer break, stretching all the way to November. Although the Institute’s more urban location within Cambridge and distance from wetlands like the Alewife Brook Reservation does lead to fewer mosquitoes, people playing sports in Briggs field or socializing on Kresge Lawn in the evenings may still be painfully aware of the insects’ presence.
This year, mosquitoes are more than just a mild annoyance. Earlier in the summer, researchers at the Massachusetts Department of Public Health announced that mosquitoes sampled around the state tested positive for West Nile virus (WNV), a generally mild but potentially serious mosquito-borne illness. Two days before the bulk of freshmen arrived at MIT for Orientation, the Boston Public Health Commission announced that a man in his 60s tested positive for WNV, the first case in Boston this year. As of time of publication, Boston is considered high-risk for the disease, and seven people have tested positive for WNV in Massachusetts this year.
What is West Nile virus?
West Nile virus is the most prevalent mosquito-borne illness in the continental U.S. and is generally spread by mosquitoes in the genus Culex. In Massachusetts, there are three common disease-spreading species in this genus, two of which primarily live near urban areas like Boston and Cambridge. Those species, Culex pipiens and Culex restuans, are most active during the summer and early fall. Nationwide, the number of people who test positive for WNV peaks around early September.
For people bitten by infected mosquitoes, there is often not much of a noticeable change in health. While around 2,000 people per year are typically diagnosed with WNV nationwide, this is generally assumed to be an underestimate of how many people actually have the disease. Mild symptoms of WNV are often confused with generic flu-like illnesses, with many infected people even being asymptomatic. However, elderly people and those with weakened immune systems or other chronic health conditions are at higher risk of more severe illness due to WNV. Severe WNV cases can cause infection of the central nervous system, resulting in swelling around the brain and paralysis. Of those with severe infections, about 10% of cases are fatal.
While most people are not at risk of serious disease or death, the city of Boston has encouraged residents to protect themselves against mosquito bites. These measures include limiting time spent outdoors between dusk and dawn, using EPA-approved mosquito repellents as directed, wearing long-sleeved shirts and long pants while outside, and removing or covering bodies of standing water.
New hope for “mosquito magnets”
For some, avoiding mosquitoes does not feel as easy as simply covering up. Some people who are fed up with constantly being bitten jokingly refer to themselves as “mosquito magnets” and resign themselves to their misfortune. While scientists still do not entirely understand which exact factors make some humans more attractive to mosquitoes than others, past research has shown that human scent plays a large role. Even then, there is likely no single recipe for becoming a “mosquito magnet,” just an unlucky combination of skin microbiota, amount of sweat, diet, and other factors.
More recently, researchers at Florida International University (FIU) led by PhD student Kaylee Marrero have discovered that even if a person is particularly attractive to one species of mosquito, they might not be as attractive to other species. Marrero and her colleagues had 119 participants take turns placing their arms in a tube separated from mosquitoes by a mesh layer and counted the number of mosquitoes attracted to the specific person. The procedure was repeated for two mosquito species, and researchers asked participants to wear a nylon sleeve for 12–16 hours for capturing scent used to measure a third species’ attraction. One of the most striking results of the study was that in most cases, no individual person was highly attractive to all three species. Marrero’s team also identified the specific compounds present in participants’ scent profiles in order to find commonalities between participants that were highly attractive to the bugs.
Though this type of per-species research is fairly new and the FIU study’s sample size was relatively small, the idea of different types of mosquitoes being attracted to differently-scented humans makes sense from an evolutionary perspective. By using distinct factors to select targets, mosquitoes could reduce competition between species. Given how complicated human scent is, even small variations like the presence or absence of a specific compound could make an impact from a mosquito’s point of view, leading to different people becoming “magnets” for different species.
The FIU team’s findings could give new hope for any self-identified “mosquito magnets” by shedding light on the specific compounds different mosquito species are attracted to. With that information, it could be possible to create regional, species-specific strategies to help people more at risk of being bitten by disease-carrying mosquitoes. Unfortunately for those in Boston, the three species Marrero’s team surveyed are currently not commonly found in Massachusetts. Until more research is carried out on other species’ preferences, the most you can do to avoid being bitten is by using broader methods: cover up, use bug spray, and limit time outside when mosquitoes are active. Thank goodness for the Infinite!