Insect-Borne Diseases Have Tripled. Here’s Why.

May 2, 2018

THE YEAR 2004 was a simpler time to be an infectious disease doctor in the US. Zika and chikungunya hadn’t yet emerged. Mystery RNA viruses weren’t spreading by tick bite around America’s heartland, killing farmers and ranchers. Certainly no one was on the lookout for a meat allergy caused by a tick with a white splotch on its back the shape of Texas. But that was then.

Since 2004, the number of people who get diseases transmitted by mosquito, tick, and flea bites has more than tripled, according to a new report released by the Centers for Disease Control and Prevention on Tuesday. Between 2004 and 2016, about 643,000 cases of 16 insect-borne illnesses were reported to the CDC—27,000 a year in 2004 (the year in which the agency began requiring more detailed reporting), rising to 96,000 by 2016. At least nine such diseases have also been discovered or introduced into the US in that same timeframe. Most of them are found in ticks. Many of them are potentially life-threatening.

What’s to blame for the surge in reported cases? Warmer weather for one thing, said the agency’s director of vector-borne diseases, Lyle Petersen, during a media briefing. Warmer temperatures allow tick populations to expand into new ranges and set up disease reservoirs where none existed before. Earlier springs and later falls also extend the length of tick season, exposing more people to risks longer. And the warmer it gets, the faster mosquitoes can breed and the higher the viral loads they carry around; outbreaks tend to occur when temperatures are higher than normal.

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