These days, many people would fill in that blank with “Lyme disease”. Lyme disease, caused by an infection with the bacterium, Borrelia burgdorferi, is the most common tick-transmitted disease of humans worldwide.

But Borrelia burgdorferi isn’t the only pathogen transmitted by ticks. It’s not even the only Borrelia.

Ticks transmit the germs responsible for over 20 significant, and sometimes deadly, human infections in addition to infections that make pets and livestock sick, too.

Most pathogens transmitted by ticks (and mosquitoes) are acquired when one stage of the tick steals a blood meal from a host* that is both infected and infective (*the term reservoir-competent describes these animals).

But there are certain pathogens that CAN be passed on from an infected female tick through the egg stage and into the next generation of ticks, a process called transovarial (t/o) transmission. Pathogens capable of t/o transmission infect at least a portion of the new larval cohort, and conceptually, can be transmitted by the larvae when they bite.

Borrelia miyamotoi is a t/o transmitted bacterium in ticks. First reported in 1995 infecting Ixodes persulcatus ticks in Japan (1), strains of this microbe also have been recovered in other Ixodes tick species, including Ixodes ricinus ticks in Europe as well as deer ticks and western blacklegged ticks in the United States.

Previously, 1.9 – 2.5% of host-seeking nymphal deer ticks collected in RI, CT, NY & NJ were shown to be infected with B. miyamotoi (2).

In a preliminary study, TERC researchers recently found that 9% of egg-laying female deer ticks collected in Rhode Island passed B. miyamotoi infection to their offspring (larvae), and this study and estimates from other scientists suggest that 6 – 73% of larvae hatching from egg batches laid by B. miyamotoi-infected females may be infected. It’s still unknown how efficiently these t/o infected larvae are in transmitting infection to humans.

In fact, until recently there was no evidence that Borrelia miyamotoi caused human infection. However, a study reported in the journal Emerging Infectious Disease in 2011 (3) reported on 46 human cases of influenza-like illness with high fever, all associated with Borrelia miyamotoi infection in Yekaterinburg City, Russia.

The study was clear that these cases WERE NOT Lyme disease. In some of the cases, a relapsing fever syndrome was observed. Other strains of Borrelia in the U.S. and elsewhere are known to cause relapsing fever.

The geographic extent of relapsing fever disease caused by Borrelia miyamotoi remains to be determined. But given the comparable tick infection rates between the Yekaterinburg region in Russia and other places where this pathogen has been detected, including here in the U.S., human infection likely does occurs outside of Russia.

Just another reason to Get TickSmart!

*TERC strongly recommends extending tick-bite protection actions into August and September to keep larval deer ticks from attaching. Wearing permethrin-treated shoes and socks is a great TickSmart practice whenever walking, camping, picnicking or enjoying other activities in the shady, wooded places where larval deer ticks thrive. Prompt removal of larvae also is encouraged *

• (1) Fukunaga et al. Genetic and phenotypic analysis of Borrelia miyamotoi sp. nov., isolated from the ixodid tick Ixodes persulcatus, the vector for Lyme disease in Japan. Int J Syst Bacteriol (1995) 45:804-810.
• (2) Scoles et al. A relapsing fever group spirochete transmitted by Ixodes scapularis ticks. Vector Borne Zoonotic Dis (2001) 1:21-34.
• (3) Platonov et al. Humans infected with relapsing fever spirochete Borrelia miyamotoi, Russia. Emerg Infect Dis (2011) 17:1816-1823.