Because the quantity of rickettsiae injected into the mice was comparable to the quantity reported in the literature for human blood during natural infections, scrub typhus could present a risk in blood collected from donors in endemic areas. This may especially be true, because people can be rickettsemic before illness, after successful antibiotic treatment, and chronically after resolution of disease.
Cell-free extracts of disrupted Renografin-purified Rickettsia typhi and R. prowazekii were evaluated as antigens in lymphocyte transformation assays for cell-mediated immunity to typhus group rickettsiae in 19 individuals with and 9 without histories of exposure to these organisms. Exposure consisted of clinical disease, vaccination with epidemic typhus vaccine, or occupational exposure to these agents. Both the soluble and membrane fractions of disrupted purified rickettsiae were used, and transformation of peripheral blood lymphocytes (PBL) was determined in microcultures by incorporation of ['H]thymidine. Of the antigen concentrations tested (1 to 400 ,tg/ml), 10,ug/ml appeared to be the most
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