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Table II.
A model (i.e. an hypothesis) of the sequence of steps for the determination of the susceptibility of a host to infection of a given LB spirochete strain/species (one component for determination of reservoir status) and transmission success from tick to vertebrate (βT-V). Susceptibility status is determined in the midgut of the feeding tick and is the outcome of interactions between the particular LB spirochete species and strain and the host species complement of the innate immune system. See text for more explanation of the tick to vertebrate transmission coefficient (βT-V) [219]. The relationship between spirochete load and βT-V may not be linear.
| Step |
I. ricinus-persulcatus complex nymph infected with a particular LB spirochete species or strain |
||
|---|---|---|---|
| Strain 1 | Strain 2 | Strain 3 | |
| (1) Host blood enters midgut of infected nymphs; spirochete population is mainly expressing OspA | Yes | Yes | Yes |
| (2) Can spirochetes bind host species-specific regulatory proteins of the complement pathway and avoid detection and destruction? (Outcome may vary with host species.) | Yes | Somewhat | No |
| (3) Spirochete status in the tick midgut | Multiplies profusely | Multiples moderately | Destroyed |
| (4) Spirochete population begins to upregulate OspC and downregulate Osp A as they migrate from the tick midgut through hemocoel to the salivary glands, and then are transmitted to the host | Yes | Yes | None |
| (5) Transmission efficiency (βT-V) to the host, if all else equal. | Higher spirochete inoculum contributes to greater βT-V | Moderate spirochete inoculum contributes to lower βT-V | No transmission (βT-V = 0) |