Published on August 15, 2016

Can Zika mosquitoes migrate to New England?

Can Zika mosquitoes migrate to New England?

With the first domestic cases of the Zika virus  now confirmed in a neighborhood in Miami, Florida, the Centers for Disease Control and Prevention has issued a warning for pregnant women to avoid that area.

So what does this mean for us living 1,500 miles away? Could the virus that can cause birth defects in infants and severe neurological illness in adults come here?

To look at the issue, OneCape Health News talked with Dr. Catherine Brown, deputy state epidemiologist and state public health veterinarian, and Gabrielle Sakolsky, assistant superintendent and entomologist for the Cape Cod Mosquito Control Project.

Two Different Types of Mosquito

The answers to these questions revolve around the two species of mosquitoes that carry the Zika virus. The main carrier of the virus is Aedes aegypti. It bites only humans, according to Dr. Brown.

“Aegypti, also called the Yellow Fever mosquito, is the really super-spreader mosquito,” she said. “Wherever they are (in large amounts) there’s a relatively high incidence of mosquito-borne disease.

“They sort of like to bar hop. The typical mosquito bites someone and gets their whole meal there. Aegypti go from person to person to bite – usually three to four people.”

According to mosquito expert Sakolsky, Aegypti has not been found on Cape Cod, and has not been known to survive in cold climates. However, the CDC posts maps online that project a future range for Aegypti mosquitoes up the East Coast through New York City and into southwestern Connecticut.

“In the future, Aegypti could be established throughout Massachusetts,” Dr. Brown said.

The less common mosquito that can serve as a Zika vector is Aedes albopictus, also known as the Asian tiger mosquito. It bites humans and animals. Unlike Aegypti, “it has gained some cold capacity,” Dr. Brown said.

The CDC map shows a range for the  Albopictus mosquito that extends through most of New England, with the exclusion of far northern Vermont and New Hampshire, and all but the southern portion of Maine. The CDC web page includes a caveat that the maps “are not meant to represent risk for spread of disease.”

Albopictus was found a few years ago in the New Bedford area near a tire recycling facility, and it may have hitched a ride via water pooled in tires sent there, according to Sakolsky. These mosquitoes prefer to breed in standing water in manmade containers, making them difficult to control. They are small, with black and white markings, and known for biting legs.

Unlike common mosquitoes, they bite in the day. On Cape Cod, they might be confused with saltwater mosquitoes that also bite during the day, but those are bigger and more aggressive, Sakolsky said.

“We have been doing surveillance for a couple of years (since Albopictus was found in New Bedford area) and we’ve never trapped one,” she said.

Of more immediate concern is the threat posed by travelling to an area where there is a Zika outbreak, or contracting one of the mosquito-borne diseases already in Massachusetts, such as Eastern Equine Encephalitis (sometimes called Triple E) or West Nile virus.

“There is some West Nile and Triple E in Massachusetts,” Dr. Brown said. “Surveillance done so far this year shows low level of Triple E, and West Nile is about moderate.”

But outbreaks of Zika will likely spread in the Deep South, where the climate favors Aegypti mosquitoes, she said.

An Expected Outbreak Pattern

“What is happening could be called expected,” Dr. Brown said. Epidemiologists tracking Zika expect it to follow patterns set by similar diseases of dengue fever and chikungunya.

“When we have seen other outbreaks they have been very small, very localized,” she said.

The case with more isolated populations, such as those on islands, is different. The New York Times reported that Dr. Lyle R. Petersen, CDC’s chief of vector-borne diseases, expects one-quarter of the residents of Puerto Rico will have been exposed to Zika by year’s end.

“We really expect a large population will be infected (in an outbreak area), and then develop an immunity,” Dr. Brown said. “You lose the ability to have an outbreak.”

“On islands, 50 to70 percent of the population (gets infected),” she said. “Once it has done that, it completely dies away.”

The following criteria must be met for an outbreak to occur, according to the CDC:

  • One of the two species of carrier mosquitoes must bite an infected person during the first week of infection when the virus is in the blood.
  • That mosquito must live long enough for the virus to multiply in its body.
  • The infected mosquito must bite another person.
  • The three steps must be repeated numerous times.

Former Cape Cod resident Melanie Lauwers, who now lives in Ft. Meyers, FL, said she is not worried about contracting Zika, nor is she concerned about the risk to her stepdaughters, ages 21 and 25, when they visit.

“Though that could change next week,” she said. “I’m a moderately young person with a pretty good immune system.”

Lauwers, the former health page editor for the Cape Cod Times, said she uses bug repellent before going out, whether in Florida or visiting Southeastern Massachusetts.

“It’s always good to be vigilant,” Sakolsky said. “We consider West Nile virus to be present in all of our towns at a low level.”

Some Tips for Avoiding Mosquito Bites

Sakolsky and Dr. Brown gave these tips for staying safe in a mosquito-friendly environment:

  • Remove any outdoor containers that could collect and hold water
  • Use EPA- approved insect repellent
  • Repair holes in window screens
  • Wear clothing that covers as much skin as possible

Of note is that Zika may be fairly harmless to most people who contract it. According to an advisory from the state Bureau of Infectious Disease and Laboratory Sciences, updated Feb. 15, 2016, about 80 percent of people infected with the virus have no symptoms. Those with symptoms first have an incubation period of three to 12 days, after which they may have fever, a rash, painful joints or conjunctivitis. These last a few days to a week.

Severe illness is uncommon, with the main exception being the children of women infected during pregnancy, who may suffer from microcephaly and other health effects.

Because the virus may live six months in men’s semen, health officials advise women who are pregnant or planning to be to use condoms during oral, anal and vaginal sex or to abstain from sex with men who may have been exposed to Zika.