NEW HAVEN, CT – Most people think of mosquitoes as a nuisance every summer, but a few of the over 3,000 types of mosquitoes can spread diseases which can be fatal. According to the Centers for Disease Control and Prevention (CDC), the mosquito is “one of the world’s most deadly animals.”
“Spreading diseases such as malaria, dengue, West Nile, yellow fever, Zika, chikungunya, and lymphatic filariasis, the mosquito kills more people than any other creature in the world,” the CDC noted on its website, adding that “in 2018, the number of severe cases of West Nile virus was nearly 25% higher in the Continental U.S. than the average incidence from 2008 to 2017.”
Last year, there was an increase in cases of Eastern Equine Encephalitis (EEE), a virus spread by infected mosquitoes which is a rare cause of brain infections (encephalitis). According to the CDC website, only a few cases are reported in the United States each year and most occur in eastern or Gulf Coast states, but approximately 30% of people with EEE die and many survivors have ongoing neurologic problems.
Greek-American Dr. Theodore Andreadis is the Director Emeritus of the Center for Vector Biology & Zoonotic Diseases of the CDC Northeast Regional Center of Excellence in Vector-Borne Diseases at The Connecticut Agricultural Experiment Station in New Haven, and Clinical Professor of Epidemiology of Microbial Disease Division at the Yale University School of Public Health. He spoke with The National Herald about mosquitoes and mosquito-borne diseases in the Northeast United States and what we can do to stay as safe as possible this summer.
Dr. Andreadis told TNH that “after 42 years at the Agricultural Experiment Station, the last six as director, I retired on April 1, nothing to do with the [corona] virus but I had already planned that, so I’m in retirement right now, I still have emeritus status, trying to keep my hands on a few things, but it’s a little bit different now, I’m not in the trenches, so to speak, any longer.”
Dr. Andreadis has expertise in the following areas: insects of medical and veterinary importance, insect pathology, microbial control of insects, mosquito biology, epidemiology of vector-borne diseases, electron microscopy, and the biology of microsporidia.
About EEE, he told TNH, “Last year was sort of an anomaly, we had never seen that much activity over such a wide geographic region. So it had been over 50 years since we had seen anything to that magnitude in terms of human cases, and so it was quite unusual and I think we just seemed to have the perfect storm going into that season with weather conditions and high populations of that particular type of mosquito that was responsible for transmitting the virus, everything came to a head very early in the season, and we don’t know what we’re going to see this year, every year is a little bit different on all of these different viruses and a lot has to do with weather conditions. For example, with EEE typically if we have a really wet summer, a mild winter, heavy rainfall and snowfall during the winter months then that will sometimes lead to high levels of activity during the summer. Now in the case of West Nile Virus, which has a totally different ecology, typically with that particular virus we see a lot of activity when we have really hot, dry summers, and especially when we have these early heat waves that come sometimes in late June when we have temperatures in the 90s here in the Northeast. These viruses are very, very different. EEE typically occurs in more rural locations because the virus is concentrated and focused in these hardwood, red maple and cedar swamps. West Nile Virus is very different, it’s more common in the densely populated urban and suburban centers because the mosquitoes that transmit that virus typically are an urban species, we call it a peridomestic, Culex pipiens, and it develops in storm drains and catch basins and when those numbers are high then we see high levels of West Nile Virus activity. So each year is very, very different, that’s why it’s so important that the states maintain their surveillance programs which generally involve trapping mosquitoes in local areas, states and various regions, and testing them for the presence of the virus and that provides an early warning system so that we know if the virus is beginning to build up in the mosquito population and then the necessary control measures have to be put in place.”
When asked about the types of mosquitoes that spread viruses, Dr. Andreadis told TNH that “there are key species that are responsible for driving these epizootics, epizootics occur in animal populations and epidemics occur in humans, with all of the viruses that we deal with in the Northeastern United States, these are all zoonotic, and what I mean by that is zoonotic diseases are caused by an organism or virus that normally occurs in wild or domestic animal populations and then can be carried over into human populations and all the viruses that are transmitted by mosquitoes here in the Northeast are all of this variety and there are a number of different types. West Nile Virus, in terms of the number of human cases, is the most prevalent and the most important followed by EEE we have some La Crosse virus that occurs, others called Jamestown Canyon, which causes mostly mild flu-like symptoms and rarely if ever would prove to be fatal. But the two most important would be West Nile which occurs every single year and EEE which is a bit more sporadic it its occurrence, at least in the Northeast. We do not have any malaria, we don’t have any Dengue, we don’t see yellow fever or Zika, or chikungunya, primarily because we don’t have the major vector of those viruses which is Aedes aegypti, that’s more of a southern tropical species that would not survive here in the Northeast.
When asked if climate change is a factor affecting mosquitoes and the spread of mosquito-borne disease, Dr. Andreadis said, “I think it’s partially a factor, it’s hard, everybody wants to say ‘this is related to climate change’ and we can’t say for certain, it’s probably a combination of factors, and some of the factors that may be involved in the reemergence and spread of EEE could be the fact that we are seeing milder winters, that seems to be fairly conclusive, and that results in greater survival of the mosquitoes during the winter months and we’re seeing warmer summers, higher temperatures which can extend the mosquito season.
“Mosquitoes will develop more quickly under warmer temperatures, they will feed more frequently on humans, on other animals, and the viruses can develop more quickly in the mosquitoes at warmer temperatures. The other factor is that we really have seen quite a bit of encroachment of suburban development especially into many of these wetland sites and there have been major changes that have occurred over the last century and if you think back to the early 1800s most of the forested areas of the Northeast were clear cut for farming and for fuel and for building houses and with the reforestation that has occurred, we are creating more habitat for these mosquitoes, developing these wetland swamps.
“A great example of that that you can see every day is you can go for a hike in these wooded areas and you will see stone walls running through these wetland sites so you know that at one time these areas were under agricultural cultivation, so you can see firsthand, so I think it’s a combination of factors, not simply climate change, but I think undoubtedly that is one piece of the puzzle here.”
When asked how people can avoid being bitten, Dr. Andreadis told TNH, “If you’re going to be out in areas with mosquito activity where they’re biting, you certainly want to use a repellant and protect yourself. And more importantly, most of the states do have these surveillance programs, they’re monitoring mosquitoes, so in a particular community or location where they report that they have found mosquitoes that are infected with EEE or West Nile Virus, then you really want to pay particular attention, avoid going into these wetland swamp areas where virus activity has been noted and if you are camping out or hiking, use a repellant to protect yourself.
“Many of these mosquitoes will bite principally during the early evening hours, or early morning when you really want to protect yourself. Generally, with a couple of exceptions, if you’re out in an open field in bright sunlight there’s not much of a risk, because most mosquitoes, there are some examples, don’t like to feed under those conditions, they like dark, shaded places so when you’re in the woods, and you know especially if you had a recent rain and you have high humidity, mosquito biting activity will be quite heavy.
When asked about ticks and Lyme Disease, Dr. Andreadis explained, “Lyme disease is transmitted by ticks and you have a much higher likelihood of picking up Lyme disease than you do of picking up any mosquito-borne disease. Lyme disease is quite prevalent in testing that we do at the Connecticut Agricultural Experiment Station, the testing done in the surrounding states as well seem to indicate that 30-40% of the ticks that are submitted for testing always test positive for Lyme disease, so it’s quite high. It’s very, very prevalent. People who are hiking, going out in the woods, exposing themselves, really need to be prudent, number one using repellant, checking yourself very, very closely when you come back, especially with the nymphal ticks that are about the size of a poppyseed. They’re really tiny, the size of a pinhead. A lot of the time people will pick these up and they’ll bite and they won’t even know that they’ve been bitten, so you really have to be cautious and we advise [people] to wear long-sleeved clothing, light colored clothing so you can see them, tuck your pants into your socks, but oftentimes in the summertime that’s not really practical, so the best way is when you come back from being out in these areas, just check yourself completely.”