A team of experts believe they’re confirmed the first U.S. case of tickborne illness caused by a particular bacteria. The case involved a 75-year-old Alabama man who likely caught the germ from a lone star tick. Thankfully, the man was successfully treated with antibiotics.
The case was detailed in last month’s edition of Emerging Infectious Diseases, a journal run by the Centres for Disease Control and Prevention. Its authors include scientists from the CDC, as well as doctors and researchers from the University of Alabama at Birmingham and the University of Washington.
According to the report, the 75-year-old Alabama resident first saw doctors at The Kirklin Clinic of UAB Hospital in April 2019. For about a month, he had been experiencing extreme fatigue along with recurring bouts of fever, chills, sweating, headache, and dizziness. The man hadn’t travelled recently, but four weeks before the trouble started, he found a tick feeding off him. Tests then revealed that he had a kind of spirochete bacteria in his blood — a broad group of spiral-shaped bacteria, some of which are known to be spread by ticks. Doctors soon placed him on antibiotics.
Following the first dose, the man developed a high fever and became stuporous (a condition in which someone becomes nearly unresponsive). But he recovered within 24 hours and finished the full course of treatment with no other issues. Over the next few months, any remaining signs of infection cleared up as well.
It would take three months to confirm the man’s diagnosis: tickborne relapsing fever (TBRF). TBRF is known to be caused by several species of Borrelia bacteria, distant cousins of the bacteria responsible for Lyme disease. But when they looked at the man’s blood under a microscope and analysed the bacteria’s genetics, they didn’t find any of these known germs; instead, they found Borrelia lonestari bacteria. Given the evidence at hand, the researchers say this is likely the first documented U.S. case of TBRF caused by B. lonestari.
B. lonestari has an interesting history. It’s frequently seen in lone star ticks and was first found to infect humans more than two decades ago. The bacteria was initially suspected as the cause of southern tick-associated rash illness (STARI), a tickborne disease with similar symptoms to Lyme, including a bull’s eye rash, spread by the lone star tick. But subsequent research failed to confirm this link, and to this day no one knows what causes STARI.
In this case, though, it’s already known that a close relative of B. lonestari, called Borrelia miyamotoi, can sometimes cause TBRF. Most TBRF infections are caused by different bacteria spread by “soft ticks,” but, if confirmed, B. lonestari would be the second TBRF germ known to be spread by hard ticks.
B. lonestari might be less able to cause disease than other notorious tickborne germs, according to the study authors. The man in this case was on immunosuppressants to keep his slow-growing lymphoma in check, which could have contributed to his illness. That said, they also note that B. lonestari is hard to identify using typical lab methods, meaning that doctors might have missed many potential cases up until now. Either way, it’s likely that we’ll eventually have a better understanding of how often it can make people sick.
“In future years, increased awareness of the pathogenic potential of B. lonestari and the use of molecular diagnostics may give us an approximation about the real burden of human illness caused by this bacterium,” study author and infectious disease specialist Vazquez Guillamet told Infectious Disease Special Edition.
In general, tickborne diseases are expected to become more common and widespread in the U.S. as tick populations continue to expand their range in a warmer climate.