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Borrelia burgdorferi, the cause of Lyme disease. from the Public Health Image Library, CDC.gov

Tickborne Diseases: Widespread, Serious, and Taking Us By Surprise

I spent most of last week at the International Conference on Emerging Infectious Diseases, a 1,500-person meeting of epidemiologists, physicians and microbiologists that is co-sponsored by the Centers for Disease Control and Prevention and the American Society for Microbiology. The ICEID, as it’s known for short, happens every two years, but this iteration was way overdue, postponed twice from its initial date of spring 2014 because so many potential attendees were working on the international outbreak of Ebola.

As a result, when this scary-disease convocation assembled, there was a lot to talk about—and in fact, a good portion of the meeting was devoted to re-examinations of the public health response, medical strategy and vaccine research that swirled around the Ebola epidemic. But at less-attended speeches, and in the afternoon hours when the newest research debuts on big posters, other public health concerns—less headline-grabbing but equally serious—peeked through.

I came away thinking we ought to be a lot more worried about ticks.

Some people already are, of course. As I described last month, the CDC has redrawn its maps of Lyme disease, the disease most commonly carried by ticks, to display how rapidly risk of it is rising in the northeastern US: 260 hot-spot counties now, compared to 69 20 years ago. (Two years ago, the CDC raised its estimate of the number of new Lyme infections that occur each year in the US from 30,000 to 300,00—10 times as much.) Also last month, the Entomological Society of America released a “policy statement” on ticks that amounted to an urgent call for action, saying in part: “…Environmental, ecological, sociological, and human demographic factors [have] created a near ‘perfect storm’ leading to more ticks in more places throughout North America.”

What’s at stake in the tickborne disease explosion flagged by the ESA and displayed in the ICEID presentations isn’t only Lyme disease (but more on that later). It is also other diseases carried by ticks—anaplasmosis, babesiosis, ehrlichiosis and more—that are less well-known and, because of that, often not detected or treated. Here, from the conference, are a few examples.

A group of researchers working at the Minnesota Department of Health suspected that the number of tickborne diseases recorded in Minnesota was too low. That’s important, because the state’s count of infections becomes part of the national record, and those numbers determine whether tick-related diseases become a priority for funding. To test the state’s record, the team randomly selected medical charts from hospitals and clinics in a Minnesota county where Lyme and its brethren are common, and checked them for billing codes that would indicate whether the patient was tested for or diagnosed with a tickborne disease. The result: There were three times more cases three times more cases of Lyme, anaplasmosis and babesiosis occurring than the state knew about.

Those high rates in Minnesota turn out not to be unusual. In Arizona, one-fourth (11 out of 42) of high school kids attending a summer football camp came down with another tick-related illness, tickborne relapsing fever. Five of the 11 had to be hospitalized. It was the largest outbreak of the disease in Arizona in 30 years. Even though they were staying in rustic cabins, the students had no idea they were in danger of ticks, and that turns out not to be unusual. In Georgia, researchers from Georgia Southern University interviewed people visiting the university health center about whether they thought they might have been exposed to ticks, and then compared the accounts with blood tests that could confirm tick bites. Out of 258 people, only 4 percent of them knew they had been bitten by a tick—but 56 percent had antibodies showing they had been bitten.

And more of us are going to have to start wondering about our risks. Until now, a built-in protection against tickborne diseases has been that the tick species that carry particular pathogens have specific geographical ranges. That’s why, for instance, Lyme disease clusters in the northern United States, while the illness that sickened the Arizona high schoolers flourishes in the Western US. But as climate change affects animal and insect ranges, those guarantees are collapsing. In Maryland, researchers for the first time have found local ticks carrying babesiosis, a parasitic infection (sometimes called “America’s malaria”) that can be passed undetected by blood transfusions and until recently has been confined to the Northeast.

New tickborne diseases are emerging as well—and often, flying under radar. Dr. Bobbi Pritt of the Mayo Clinic described an illness that affected two men seeking care at a Mayo satellite clinic in Eau Claire, WI: one a healthy 54-year-old who liked to spend time outdoors and was bitten by a tick at a woodland cabin, the other a 23-year-old cystic fibrosis patient, recovering from a double lung transplant, who was bitten in his own backyard. Thanks to alert lab workers who noticed the men’s test results were a little off—a finding later backed up by a US Army lab, and then by the CDC—the cause was identified as a never before seen infection related to a tickborne illness carried by mice. The disease is so new that the organism hasn’t yet been given a name (Ehrlichia muris eauclairensis has been proposed, to mark the location where it was first spotted), but already, Pritt said, 80 patients have been identified in five states. One-third had to be hospitalized. It’s not clear how wide a range the disease might have.

Finally—because descriptions of tick-related diseases seem to focus on fever and headache and not very serious-sounding symptoms—it was troubling to be reminded by Dr. Paul Mead of the CDC how serious Lyme in particular can be. He described the national detective work that swung into action after a young Massachusetts resident passed out while behind the wheel of a car; the car rolled to a stop, paramedics attempted to revive him, and when he could not be brought back, his tissues were given for transplant. A careful worker at a tissue bank noticed signs of inflammation inside his heart—and that led to a discovery that the victim’s undiagnosed Lyme disease had caused sudden cardiac death. Scouring patient reports, Mead said, revealed 45 patients who survived “heart block”—an interruption of the heartbeat—because of Lyme infection, and five others who died when their Lyme disease triggered what looked like a heart attack.

I’ve written elsewhere about the recent recognition of Heartland virus, Powassan virus and Borrelia miyamotoi in the US, and additional tickborne diseases in places as far apart as China (severe fever with thrombocytopenia) and Sweden (Neoehrlichia mikurensis). But to hear so many reports in such a short period of time just underlines: Tickborne diseases are increasing, in range and in severity. Whatever we’re doing to protect ourselves, it isn’t enough.