B miyamotoi disease is an emerging spirochetal disease caused by B miyamotoi subspecies, which are taxonomically closely related to Borrelia recurrentis and Borrelia hermsii, the agents of relapsing fever. Like Lyme disease, it is tick-borne via hard Ixodes ticks. It is not transmitted via the soft ticks associated with the Borrelia species that cause relapsing fever.
B miyamotoi is commonly found in regions with Lyme disease. It was initially identified as a cause of febrile illness in Russian adults and has subsequently been documented in North America and Europe as well.
Unlike B burgdorferi, the causative agent of Lyme disease in which the nymph or adult tick transmits the infection, B miyamotoi can be vertically transmitted to larval Ixodes ticks. In the United States, this can cause a shift in the peak months during which the risk of human disease is highest. The peak season for Lyme disease is late fall while the peak for B miyamotoi disease is into the summer and early fall. An additional contrast is that B miyamotoi disease may occur shortly after attachment of an infected tick, while Lyme disease risk is highest after 36–48 hours of attachment and feeding on a human host.
The epidemiology is evolving as new data come in, but the prevalence of B miyamotoi in different species of Ixodes ticks in the northern United States is generally 5% or less, compared to up to 30% for B burgdorferi. Rodents and birds are reservoirs for B miyamotoi.
Fever occurs in almost all cases. In contrast to Lyme disease, rashes are uncommon (less than 10% of cases). Symptoms may include severe systemic symptoms of fatigue, myalgia, chills, and nausea. Patients are often more acutely ill and likely to require hospitalization than with Lyme disease. In more severe disease or in elderly or immunocompromised patients, meningoencephalitis, headache, or cognitive impairment can predominate. While the fever of B miyamotoi disease can wax and wane, there is not an acute presentation as in true relapsing fever disease due to B recurrentis or B hermsii.
Laboratory findings include leukopenia, thrombocytopenia and elevated liver biochemical tests. If available, PCR of blood or CSF samples drawn during acute disease is recommended to detect B miyamotoi; negative results do not necessarily rule out B miyamotoi disease because laboratories may vary in expertise. If PCR is not available, spirochetes may sometimes be visualized on a blood smear using Wright or Giemsa-stain or by darkfield microscopy of CSF.
If using the recommended two step testing algorithm for B burgdorferi (EIA followed by immunoblot), the EIA may be positive in B miyamotoi disease due to cross-reactivity but the confirmatory immunoblot will be negative. This may be an indication that B miyamotoi, ...