The Mosquito-Borne Disease 'Triple E' Is Spreading In the US As Temperatures Rise

An anonymous reader quotes a report from Wired: A 41-year-old man in New Hampshire died last week after contracting a rare mosquito-borne illness called eastern equine encephalitis virus, also known as EEE or 'triple E.' It was New Hampshire's first human case of the disease in a decade. Four other human EEE infections have been reported this year, in Wisconsin, New Jersey, Massachusetts, and Vermont. Though this outbreak is small, and triple E does not pose a risk to most people living in the United States, public health officials and researchers are concerned about the threat the deadly virus poses to the public, both this year and in future summers. There is no known cure for the disease, which can cause severe flu-like symptoms and seizures in humans four to 10 days after exposure and kills between 30 and 40 percent of the people it infects (Warning: source paywalled; alternative source). Half of the people who survive a triple E infection are left with permanent neurological damage. Because of EEE's high mortality rate, state officials have begun spraying insecticide in Massachusetts, where 10 communities have been designated 'critical' or 'high risk' for triple E. Towns in the state shuttered their parks from dusk to dawn and warned people to stay inside after 6 pm, when mosquitoes are most active.

Like West Nile virus, another mosquito-borne illness that poses a risk to people in the US every summer, triple E is constrained by environmental factors that are changing rapidly as the planet warms. That's because mosquitoes thrive in the hotter, wetter conditions that climate change is producing. 'We have seen a resurgence of activity with eastern equine encephalitis virus over the course of the past 10 or so years,' said Theodore G. Andreadis, a researcher who studied mosquito-borne diseases at the Connecticut Agricultural Experiment Station, a state government research and public outreach outfit, for 35 years. 'And we've seen an advancement into more northern regions where it had previously not been detected.' Researchers don't know what causes the virus to surge and abate, but Andreadis said it's clear that climate change is one of the factors spurring its spread, particularly into new regions.

Studies have shown that warmer air temperatures up to a certain threshold, around 90 degrees Fahrenheit, shorten the amount of time it takes for C. melanura eggs to hatch. Higher temperatures in the spring and fall extend the number of days mosquitoes have to breed and feed. And they'll feed more times in a summer season if it's warmer -- mosquitoes are ectothermic, meaning their metabolism speeds up in higher temperatures. Rainfall, too, plays a role in mosquito breeding and activity, since mosquito eggs need water to hatch. A warmer atmosphere holds more moisture, which means that even small rainfall events dump more water today than they would have last century. The more standing water there is in roadside ditches, abandoned car tires, ponds, bogs, and potholes, the more opportunities mosquitoes have to breed. And warmer water decreases the incubation period for C. melanura eggs, leading one study to conclude that warmer-than-average water temperatures 'increase the probability for amplification of EEE.' Climate change isn't the only factor encouraging the spread of disease vectors like mosquitoes. The slow reforestation of areas that were clear-cut for industry and agriculture many decades ago is creating new habitat for insects. At the same time, developers are building new homes in wooded or half-wooded zones in ever larger numbers, putting humans in closer proximity to the natural world and the bugs that live in it. The report notes that the best way to prevent mosquito bites is to 'wear long sleeves and pants at dusk and dawn, when mosquitoes are most prone to biting, and regularly apply an effective mosquito spray.' Local health departments can also help protect the public by 'testing pools of water for mosquito larvae and conducting public awareness and insecticide spraying campaigns when triple E is detected,' notes Wired.

A vaccine for the disease exists for horses, but because the illness is so rare 'there is little incentive for vaccine manufacturers to develop a preventative for triple E in humans,' adds the report.

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