B. hermsii are transmitted to humans through the bite of infected soft-bodied ticks of the genus Ornithodoros. These ticks usually live within rodent burrows, feeding on the rodent as it sleeps. Humans typically come into contact with Ornithodoros spp. ticks when they sleep in rodent-infested cabins, where ticks emerge to feed briefly on the person who is sleeping. Unlike hard-bodied ticks (e.g. Ixodes spp and Dermacentor spp), which can burrow into human skin for days, soft-bodied ticks feed quickly, usually lasting less than half an hour. Due to the short period of attachment to humans and typically during sleep, most people do not find a tick on themselves and may be unaware that they have been bitten. Transmission from mother to fetus is also known to occur.
