In a US first, a case of tickborne relapsing fever caused by a particular species of bacteria has been reported, according to the Centers for Disease Control and Prevention (CDC). The pathogen in question is Borrelia lonestari, a distant relative of the bacteria responsible for Lyme disease, which has never before been found to cause this particular illness.
Tickborne relapsing fever (TBRF) is a rare infection characterized by recurring fever, headaches, muscle and joint aches, and nausea. It is most common in the western US and is often linked to sleeping in rustic, rodent-infested mountain cabins. The condition is known to be caused by Borrelia bacteria – although not B. lonestari, until now – transmitted to humans through the bite of infected “soft ticks”.
The unusual case was reported last month in the CDC-run journal Emerging Infectious Diseases and involved a 75-year-old man from Alabama. Back in 2019, he reported experiencing relapsing fevers, as well as chills, sweating, headache, dizziness, and fatigue for around a month. He admitted to having removed a tick several weeks prior to his symptoms emerging. Fortunately, he was successfully treated with antibiotics.
Doctors initially identified spirochetes – spiral-shaped bacteria often spread by ticks – in his blood, and after months of investigation arrived at a diagnosis of TBRF caused by B. lonestari.
B. lonestari was first detected in the lone star tick in 1996 and was found to infect humans over 20 years ago. A close relative of these bacteria, called B. miyamotoi, which is transmitted by hard ticks, is known to cause TBRF.
“This case report sheds light onto the potential of B. lonestari to cause human illness and contributes to the body of knowledge on TBRF,” study author Dr Laia J. Vazquez Guillamet told Infectious Disease Special Edition. “It is the second tickborne Borrelia species transmitted by hard ticks that has been identified as a causative agent of relapsing fever, being the previous ones [were] transmitted by soft ticks.”
It is important to note, however, that the patient was on immunosuppressant drugs for lymphoma, meaning it’s not possible to tell whether he developed TBRF because B. lonestari is particularly pathogenic or because his medication made him more susceptible to infection.
“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,” Vazquez Guillamet added.
The study is published in Emerging Infectious Diseases.