Rickettsia are zoonotic obligate intracellular bacteria of the family Rickettsiaceae. They are associated with arthropods, primarily ticks, but also including fleas, body lice and mites, which serve as the main reservoirs. These arthropods serve as vectors of rickettsiosis while feeding on both humans and animals.
The antibody response to infections by these agents is primarily directed against group-common (spotted fever or typhus groups) lipopolysaccharide (LPS) and 2 outer-membrane attachment proteins (OmpA and OmpB). The standard IFA and MIF methods detect antibody against the whole organism and remain the most commonly used diagnostic methods, not necessarily the best. IgM-specific antibody assays are particularly prone to false-positive reactivity with whole cell antigens due to the LPS antigen.
Typhus group (TG) Rickettsia
The antibody response to infections by these agents is primarily directed against group-common (typhus group) lipopolysaccharide (LPS) and 1 outer-membrane protein (OmpB). The standard IFA and MIF methods detect antibody against the whole organism and remain the most commonly used diagnostic methods, not necessarily the best.
For Rickettsia typhi and R. prowazekii the IgG ELISA utilizes both OmpB and TG LPS, while the IgM assay utilizes purified native OmpB (LPS-free). A 2-antigen MIF assay (FBT-12 slides) is available for R. typhi and R. felis in flea-borne typhus testing. For additional information see Flea-borne Typhus Poster
Spotted fever group (SFG) Rickettsia
For SFG species our ELISA IgG assay (SFG-96K) utilizes purified LPS, the major acute-phase reactant, to specifically detect reactivity to all SFG species equally. The LPS antigen is group specific, but parsing individual species requires a panel of multiple purified LPS-free protein antigens, each of which is surprisingly specific in the IgG assay, but such a panel is not for routine diagnostic use.
For SFG IgM the opposite is true, although the protein antigens must be totally LPS-free. The reactivity of IgM antibody is group-common to the β-peptide associated with the OmpB protein of both SFG and TG species. This recombinant antigen is LPS-free, avoiding the high level of non-specific responses (false-positive) due to the use of whole cell antigens (IFA and MIF tests). Please note information detailed in our 2018 ASR Poster presentation.
For more information on specific Rickettsia species and associated products click here.