A recently identified tick-borne illness has been detected in 2 patients in the northeastern United States, according to case reports published today in the Annals of Internal Medicine as the US tick season begins to ramp up.
In 1995, when Japanese researchers identified the pathogen that causes this illness, a new species of Borrelia bacteria called Borrelia miyamotoi, their work marked a new approach to identifying a novel infectious disease, according to an editorial published alongside the study. Most new diseases are identified after a person becomes ill, but these researchers sought to identify potential disease-causing agents in a known vector of other human pathogens, a tick of the Ixodes genus that transmits a related Borrelia bacterium that causes Lyme disease in Japan and elsewhere. The discovery subsequently led to the identification of B miyamotoi in ticks in Eurasia and North America. By 2011, human cases of illness associated with B miyamotoi infection had been documented in Russia.
The first reports of cases in US patients, documented earlier this year and described in the report published today, suggest that some cases of B miyamotoi may be misdiagnosed as human granulocytic anaplasmosis (HGA), a tick-borne disease caused by the bacteria Anaplasma phagocytophilum. The multi-institution team of researchers used a polymerase chain reaction assay and DNA sequencing to identify B miyamotoi in the blood of 2 patients with presumed HGA who exhibited a delayed response to therapy with doxycycline.
One patient, a 61-year-old man from Massachusetts, was hospitalized with fever, chills, and pain, and blood tests revealed signs of likely infection. The man received a presumptive diagnosis of HGA and was given intravenous doxycycline, but the man’s fever persisted for 3 days instead of responding almost immediately, which is expected in patients with HGA. He eventually recovered. The second patient, an 87-year-old man from New Jersey, was admitted to the hospital with similar symptoms. The lack of an immediate response to treatment and a failure to detect signs of A phagocytophilum led to the testing that ultimately identified B miyamotoi as the cause of the patients’ symptoms.
The researchers conclude that physicians should be aware that B miyamotoi infection is a possible cause of HGA-like symptoms, especially in individuals who don’t respond quickly to doxycycline. Sam R. Telford III, ScD, a professor of infectious diseases at Tufts University’s Cummings School of Veterinary Medicine, explained that B miyamotoi is susceptible to doxycycline, but other tick-borne illnesses are not. Of particular concern is babesiosis, which doesn’t respond to doxycycline and can persist in the blood of asymptomatic individuals, posing a threat to the blood supply.
“Be aware that there are a number of infectious agents transmitted by ticks,” said Telford. He said physicians appropriately begin treatment for suspected tick-borne illnesses before the cause has been confirmed, but suggests that testing to find the precise infectious agent will aid public health efforts.
Much remains to be learned about B miyamotoi infections, caution the authors of the editorial, noting that the range of illness from this infection and its prevalence are unknown. In fact, they note its prevalence may be quite low, since studies have suggested far fewer ticks carry B miyamotoi than the bacterium that causes Lyme disease.