Eastern equine encephalitis (EEE), a deadly viral pathogen transmitted to humans by mosquitoes, has claimed one life in Massachusetts this year, and infected six other people. Several Massachusetts communities have been designated critical and high-risk zones for EEE by the Massachusetts Department of Public Health (DPH). Martha’s Vineyard is not among them.
Along with the Elizabeth Islands, the Vineyard was designated a remote risk zone. Per a DPH chart, remote risk means “EEE is not usually found in your area.” For remote risk, no preventive measures are recommended on the DPH chart. The two preparatory measures recommended are to repair screens and to check the DPH website. On the other end of the scale, in critical risk communities, Wareham and New Bedford among them, “an excessive risk of EEE exits.” Outdoor activities between dusk and dawn, “peak mosquito hours,” are recommended to be canceled or rescheduled in those communities. Falmouth, which anyone traveling aboard an SSA ferry from the Island has to go through, is a moderate risk community. The same DPH chart recommends wearing mosquito repellent when outdoors between dusk and dawn, and avoidance of “outside areas with obvious mosquito activity” in such a risk zone.
No mosquitoes captured by a longstanding Dukes County survey program have ever tested positive for EEE, according to Edgartown health agent Matt Poole. However, Tufts University researcher Sam Telford said one of the mosquitoes believed to be a carrier of the virus, Culiseta melanura, the black-tailed mosquito, can be found in Chilmark’s swamps. “They’re certainly there,” he said.
Asked if EEE could be found in those swamps, Telford said, “Likely, if I were to sample.”
Telford, who is known for his acumen on tick ecology and pathogens, is part of a state advisory committee on mosquitoes.
The black-tailed mosquito, he said, breeds in the water-filled hollows and crooks of trees found in swampland. Because of this, he said, they are “very hard to control.”
However, he said, the black-tailed mosquito isn’t thought to bite people, only birds. Therefore it can perpetuate a mosquito-bird reservoir of EEE, though it isn’t suspected of passing it to humans.
But another hollow- and crook-breeding mosquito,Telford said, Coquillettidia perturbans, the cattail mosquito, does bite people, and is the chief culprit in the Massachusetts cases. Telford said he believes it is probable the mosquito is on the Vineyard. A reed dweller, the cattail mosquito appears to enjoy dining on red-winged blackbirds and other migratory birds known to lay over on the Vineyard, he noted.
One reason why EEE has yet to turn up in county mosquito surveys is because Dukes County doesn’t trap either the black-tailed or cattail mosquitoes as a matter of course, according to Dick Johnson, who runs the program. Johnson said the county employs gravid traps, which capture a range of mosquitoes, but not those two, which require a light trap. The gravid traps catch native mosquitoes of Culex genus, Johnson said, which are difficult to differentiate by species, and also nonnative species from Japan and elsewhere. The goal is to look for West Nile virus, which in rare instances can cause brain inflammation like EEE. In 2013 and 2018, mosquitoes were collected by Johnson that tested positive for West Nile virus at a state laboratory. These amounted to five mosquitoes out of thousands harvested.
A terrible pathogen
Telford described EEE as “the worst vector-transmitted virus arguably one can get in North America.” Telford, who runs the New England Regional Biosafety Laboratory, said the federal government classifies EEE, along with pathogens like tularemia and anthrax, as a weaponizable danger.
Telford said EEE can present like meningitis, with a sudden, high fever and stiff neck. Antivirals are ineffective against EEE, he said, and typically there is little beyond palliative care that hospitals can provide. He said typically 30 percent of people who get an EEE cerebral infection die.
Those who survive are “so disabled neurologically they need special care,” he said. “Many of the survivors die within six years.”
Telford described EEE as a rapid cell-killer that progresses through the body more swiftly than other similar diseases like Russian spring-summer encephalitis or rabies.
Like with tick-borne Powassan virus and deer tick virus, Telford said, the young, the elderly, and the immunocompromised are most at risk for contracting EEE, but “no one is immune.”
Telford emphasized EEE isn’t common. “It’s a rare disease in the U.S. — not more than 20 cases a year.”
He also said not everyone infected with the virus develops encephalitis. People can be infected with EEE and mainly develop an “abrupt fever,” from which they survive without neurological damage.
Telford deemed it improbable an infected mosquito from a zone deemed more dangerous in Massachusetts, even Falmouth, would slip into a ferry-bound car or into a Steamship Authority ferry’s vehicle bay and hitch a ride over to the Vineyard.
Mosquito Report on the horizon
Steve Rich, director of the University of Massachusetts, Amherst, Laboratory of Medical Zoology, and a colleague of Telford’s in tick research, told The Times an infected mosquito crossing Vineyard Sound on a ferry isn’t out of the question. “That’s a possibility,” he said.
Rich pointed to a phenomenon known as “airport malaria.”
“‘Airport’ malaria,” according to the Centers for Disease Control, “refers to malaria caused by infected mosquitoes that are transported rapidly by aircraft from a malaria-endemic country to a nonendemic country. If the local conditions allow their survival, they can bite local residents, who can thus acquire malaria without having traveled abroad.”
In mentioning airport malaria, he cautioned that the prevalence of malaria is “astoundingly higher” than EEE, with hundreds of millions of people across the globe infected with malarial parasites annually. Rich said the black-tailed mosquito is probably on Martha’s Vineyard in very small numbers. He agreed EEE progresses rapidly, especially compared to rabies, which due to its relative sluggishness at traveling from a bite wound to the brain frequently provides time for medical intervention to stymie the virus.
Rich’s lab became the “nation’s mosquito testing laboratory” last year when the National Science Foundation’s National Ecological Observatory Network (NEON) greatly upped the number of mosquitoes it sent to UMass, with 15,000 vials (50 mosquitoes per vial) from 47 sites across North America.
“We’ve been testing ticks for NEON for a couple years, and we’re excited to now become the nation’s mosquito testing laboratory,” Rich said in a release last year. “This is a great opportunity for our state, since there is great interest in spread of mosquitoes in Massachusetts. Our lab will test these mosquitoes for a variety of known viruses such as Eastern equine encephalitis, West Nile virus, Zika, and dengue, plus a number of unknown viruses.”
Rich told The Times the mosquitoes are being tested as part of a massive ecological data analysis that will span 30 years, and is meant to study particular environments over time, including one in the Harvard Forest in Petersham.
Rich’s lab presently offers tick testing through Tick Report, a service where anyone can mail in a tick and learn what pathogens it harbors. By 2020, Rich said his lab intends to offer similar services for mosquitoes. Unlike Tick Report, Mosquito Report, as he said it will be called, won’t take one sample at a time, but a minimum of 50. This means, he said, those who send in mosquitoes will need to have a trap of some kind available to them. Rich also said his lab is refining the process of mosquito testing because there’s a “big difference” in analyzing mosquitoes. Rich said there are compounds in mosquito bodies, particularly mosquito eyes, that interfere with enzyme analysis. His team is taking additional steps, he said, so that the mosquito assays in his lab, which are already precise, will be so accurate that they will be considered the “gold standard” of mosquito testing.
Poole said even though the Vineyard has not risen above the lowest level of DPH concern, “we’re not risk-free by any means.”