Lyme Disease Microbiology - Life Cycle

Life Cycle

The life cycle of B. burgdorferi is complex, requiring ticks, rodents, and deer at various points. Mice are the primary reservoir for the bacteria; Ixodes ticks then transmit the B. burgdorferi infection to deer.

Hard ticks have a variety of life histories with respect to optimizing their chance of contact with an appropriate host to ensure survival. The life stages of soft ticks are not readily distinguishable. The first life stage to hatch from the egg, a six-legged larva, takes a blood meal from a host, and molts to the first nymphal stage. Unlike hard ticks, many soft ticks go through multiple nymphal stages, gradually increasing in size until the final molt to the adult stage.

The life cycle of the deer tick comprises three growth stages: the larva, nymph and adult.

The life-cycle concept encompassing reservoirs and infections in multiple hosts has recently been expanded to encompass forms of the spirochete which differ from the motile corkscrew form, and these include cystic spheroplast-like forms, straight non-coiled bacillary forms which are immotile due to flagellin mutations and granular forms, coccoid in profile. The model of Plasmodium species malaria, with multiple parasitic profiles demonstrable in various host insects and mammals, is a hypothesized model for a similarly complex proposed Borrelia spirochete life cycle.

Whereas B. burgdorferi is most associated with deer tick and the white footed mouse, B. afzelli is most frequently detected in rodent-feeding vector ticks, and B. garinii and B. valaisiana appear to be associated with birds. Both rodents and birds are competent reservoir hosts for Borrelia burgdorferi sensu stricto. The resistance of a genospecies of Lyme disease spirochetes to the bacteriolytic activities of the alternative immune complement system of various host species may determine its reservoir host association.