Rickettsia prowazekii is the agent of epidemic typhus. It’s only known host, outside of the instances of human prison camps and similar louse-infested conditions, is the flying squirrels of the eastern U.S. The vector of infection is generally the human body louse, which can transmit infection from person to person. The itching and attendant scratching of louse bites allows the introduction of infected louse feces into the bloodstream via skin abrasions. There is evidence that ticks and fleas may also be a part of the natural cycle of this organism.

Serologic tests for typhus group Rickettsia show very strong cross-reactivity between R. typhi and R. prowazekii. Both MIF and IFA tests are more sensitive to the LPS antigen, which is totally cross-reactive, and the OmpB protein antigens are nearly as strongly cross-reactive. Serologic differentiation of these two species relies on reciprocal cross-absorption studies, an expensive research protocol until it is commercially developed. Fortunately this product should be available here by June-July 2015.

The ELISA antigen currently used is a full-length OmpB passenger domain, but we are transitioning to the use of a recombinant OmpB passenger domain. This antigen has been provided with native methylation enzymatically in order to be as sensitive and specific as the antigen that previously was purified from live R. prowazekii.