The only reasonable prevention is to be strong enough [vitality] to throw off the illness. This means that prior to being bitten , one has so strengthened the vitality by constitutional means , that it is able to deal with any problem.

As Clarke pointed out - using V Grauvogl's words - " From the same cause , on the same day , and indeed in the very same hour , one may get a syphilitic ulcer, one a sycotic ulcer and one escape without any infection".

Thr point being that there is a predisposition involved in any infection.