Absence of transovarial transmission of Borrelia duttonii, a tick-borne relapsing fever agent, by the vector tick Ornithodoros moubata.

We examined the vector competence of the tick, Ornithodoros moubata, using laboratory-reared gerbils as hosts. Transmission of the relapsing fever agent Borrelia duttonii occurred efficiently from infected ticks to uninfected gerbils and from infected gerbils to uninfected ticks. Spirochetes were maintained stably in the ticks for at least 3 months, but they disappeared from the bloodstream of infected gerbils after three episodes of spirochetemia. We also examined transovarial transmission of B. duttonii during the gonotrophic cycle and filial generation. No spirochetes could be detected from the offspring generation of the ticks by culture and polymerase chain reaction (PCR) methods, although spirochetes were still found in the female ticks. The results indicate that, because of the rarity of transovarial infection, the role of transovarial passage of B. duttonii to eggs and larval O. moubata ticks is limited in maintaining B. duttonii. Our findings strongly suggest that B. duttonii is maintained through the O. moubata tick-human transmission cycle in tick-borne relapsing fever endemic areas.