the onset of symptoms for there to be diagnostically significant titers of r. tyhpi. and so the diagnosis is often confirmed after the patient has either recovered or died. r. typhi are not able to grow in axenic or sterile conditions, and must be grown in tissue, or embryo samples. even when stringent physiologic conditions are met, when grown in media that mimics the environment of host cytoplasm, pathogen activity cannot survive very long. a common method for growing r. typhi is through the yolk sacs of embryonic eggs. laboratory techniques such as real-time pcr and microimmunofluorescence can be used to identify rickettsia down to the species level. microimmunofluorescence is a highly sensitive test that is often used in endemic areas to confirm infection by r. typhi. the use of real-time pcr can allow for the detection and confirmation of r. typhi earlier than serological tests. membrane protein ompb and prsa gene fragments have been shown to be identifiable markers in qpcr for r. typhi. vitellus or "yolk" of an embryonic egg is a commonly used site for growth of the obligate intracellular bacterium r. typhi differentiation from r. prowazekii symptoms of r. typhi and r. prowazekii can be very similar, with r. typhi infections usually being less severe. r. typhi and its typhus group member r. prowazekii are composed of very similar genomes, r. typhi can be differentiated from r. prowazekii by 12000 base pairs inserted into r. prowazekii. there are various methods to differentiate among the typhus group members. one method is through restriction fragment length polymorphism (rflp), which can differentiate the two species based on the ompb gene and associated enzymes, which has a unique sequence for each species. serological methods are also useful. it has been shown that utilizing indirect fluorescent antibody assays and western blot analysis together provide reliable differentiation among the species. serum cross-adsorbent analysis alone is also a reliable method for differentiation, as cross reaction between the two species is common. bibliography mcleod, michael p.; qin, xiang; karpathy, sandor e.; gioia, jason; highlander, sarah k.; fox, george e.; mcneill, thomas z.; jiang, huaiyang; muzny, donna; jacob, leni s.; hawes, alicia c. 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