Invasive Ticks Carrying New Diseases Are Spreading Through the Northeast

New species of ticks are moving to the Northeastern U.S.—and bringing along unfriendly visitors with them. In a recent study, scientists have reported the first human case of a particular tickborne bacteria in Connecticut and the greater Northeast region. The bacteria are being spread by ticks that were previously confined to the Gulf Coast but have since begun to emerge north.

Ticks and the microbes they transmit to people and other animals via their bloodsucking have become an increasingly bigger public health problem in recent years. While Borrelia burgdorferi, the bacteria that causes Lyme disease, remains the most common tickborne germ, other pathogens are becoming more prevalent in endemic areas or are emerging in new places, including the bacteria Rickettsia parkeri. The scientists behind this new research, published last month in the journal Emerging Infectious Diseases, are now warning that R. parkeri has clearly made itself comfortable in Connecticut and likely beyond.

The growing tick threat

Infections caused by Rickettsia bacteria are broadly known as rickettsiosis, with the most well-known of these diseases being Rocky Mountain spotted fever (RMSF). As the nickname suggests, the most common symptoms of RMSF are fever, headache, and rashes starting along the wrists and ankles that can extend widely throughout the body. However, more serious cases can lead to life-threatening complications like organ damage, especially if not treated promptly with antibiotics. R. parkeri infections tend to cause symptoms similar to but generally milder than RMSF, though it can be difficult to tell the two apart early on.

In 2021, researcher Goudarz Molaei and others published a study showing that the Gulf Coast tick (Amblyomma maculatum)—the primary vector of R. parkeri in the U.S.—had established a population in Connecticut, while other studies have found populations living in New York and New Jersey. A substantial proportion of the ticks that his team discovered—about 30%—were also found to carry R. parkeri, though no human R. parkeri infections were reported in the area back then. Still, Molaei suspected that it would only be a matter of time before such reports would show up.

“At the time, we raised awareness, but some of the agencies, they did not even believe that there would be human cases,” Molaei, director of the Tick Testing Program for Lyme and Allied Diseases at the state-run Connecticut Agricultural Experiment Station (CAES), told Gizmodo over the phone. Just two years later, his fears would be confirmed.

A fortunate intervention

The case involved a 29-year-old woman who found a tick at the nape of her neck after visiting a beach in Fairfield County in August 2023. The tick was sent to Molaei’s team at CAES, where it was confirmed to be a Gulf Coast tick. Due to the busy season, Molaei initially didn’t test the tick for anything, but he was curious enough to reach out to the health department to see how the patient was faring.

He soon learned that she wasn’t doing so great, and both he and a technician drove out to Fairfield to meet with the patient and her doctor. He explained that the tick they found wasn’t the typical blacklegged tick responsible for Lyme disease; that same day, he tested and eventually confirmed the woman’s tick to be carrying R. parkeri. With his help, the woman’s blood was collected and also later confirmed to test positive for R. parkeri by the Centers for Disease Control and Prevention, and she was given a different course of antibiotics to treat the infection. The woman subsequently made a speedy recovery.

Factors behind the spread

While this case may have a happy ending, the expanded and now continued presence of R. parkeri in the state doesn’t bode well for the rest of us. There are several reasons why this and other tickborne germs are widening their range. For instance, one factor could be the restoration and preservation of grassland habitats, the Gulf Coast tick’s preferred environment, in states like Connecticut or New York (the researchers highlight the former Freshkills landfill, now a park, in Staten Island as a example). But make no mistake about it, climate change is a major driving force in making ticks a bigger problem in the U.S.

“For those native tick species that we have, like blacklegged ticks, climate change causes those tick species to move further north. But when it comes to invasive species, this provides a conducive environment for them once they land here,” Molaei said. With Gulf Coast ticks, it’s likely that they were brought to the Northeast via migratory birds. And the milder winters now common in the region mean that they’re able to survive the cold and establish a sustained foothold.

Molaei, who also is a tick and mosquito researcher at the Yale School of Public Health, notes that local and federal agencies are now making a more concerted effort to study, track, and hopefully mitigate the tick invasion. His team at CAES and Yale are working on several projects to better understand the spread of R. parkeri and other tickborne diseases in the area, including the rare condition that makes someone allergic to red meat, which has become a growing local issue. He adds that only some invasive tick species that have arrived in a new part of the U.S. have been able to establish local populations. But the team’s research also shows that we’re not going to be lucky every time.

So Americans, especially people living in the Northeast and other tick hot spots, will need to be more vigilant about tick prevention and detection moving forward. Common tips for avoiding ticks include using EPA-approved repellents and wearing long-sleeved clothing when visiting woody or grassy areas, and making sure to check yourself (and your pets) for ticks after coming inside. This particular case also illustrates the importance of holding onto any ticks that manage to bite and potentially sicken you.

“There is a need for doctors and patients in our state and throughout the northeastern U.S. to recognize that we are dealing with several invasive tick species, and each one of these tick species carry their own diseases,” Molaei said. “Therefore, once someone is bitten by a tick, it’s absolutely important for them to at least get the tick identified. If they don’t want to get it tested, fine, but if they can identify the tick, then they and their primary care physicians will be in a better position to assess the risk of infection with different tickborne diseases, and to come up with proper and prompt treatment.”