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Differentiation of murine typhus due to Rickettsia typhi and epidemic typhus due to Rickettsia prowazekii is critical epidemiologically but difficult serologically. Using serological, epidemiological, and clinical criteria, we selected sera from 264 patients with epidemic typhus and from 44 patients with murine typhus among the 29,188 tested sera in our bank. These sera cross-reacted extensively in indirect fluorescent antibody assays (IFAs) against R. typhi and R. prowazekii, as 42% of the sera from patients with epidemic typhus and 34% of the sera from patients with murine typhus exhibited immunoglobulin M (IgM) and/or IgG titers against the homologous antigen (R. prowazekii and R. typhi, respectively) that were more than one dilution higher than those against the heterologous antigen. Serum cross-adsorption studies and Western blotting were performed on sera from 12 selected patients, 5 with murine typhus, 5 with epidemic typhus, and 2 suffering from typhus of undetermined etiology. Differences in IFA titers against R. typhi and R. prowazekii allowed the identification of the etiological agent in 8 of 12 patients. Western blot studies enabled the identification of the etiological agent in six patients. When the results of IFA and Western blot studies were considered in combination, identification of the etiological agent was possible for 10 of 12 patients. Serum cross-adsorption studies enabled the differentiation of the etiological agent in all patients. Our study indicates that when used together, Western blotting and IFA are useful serological tools to differentiate between R. prowazekii and R. typhi exposures. While a cross-adsorption study is the definitive technique to differentiate between infections with these agents, it was necessary in only 2 of 12 cases (16.7%), and the high costs of such a study limit its use.

A sensitive assay based on the polymerase chain reaction for the detection of Ockelbo virus RNA was developed. Two primer pairs from the gene coding for the E2 glycoprotein were chosen. By use of a nested strategy for the primers, as few as 1 to 10 PFU could be detected. The amplified products were visualized as bands of appropriate size on ethidium bromide-stained agarose gels. The primer pairs allowed amplification of several Ockelbo and Sindbis virus isolates but discriminated between these and other alphaviruses. Ockelbo virus RNA was detected in 4 of 10 skin biopsy specimens collected during the acute stage of the disease. The identities of the amplified products were confirmed by restriction endonuclease cleavage. Acute- and convalescent-phase sera as well as lymphocytes collected during the convalescent phase were negative by the polymerase chain reaction. No infectious virus could be recovered from any of the specimens.

Since April 1986, microimmunofluorescence assays have been employed at the Department of Virology at the National Bacteriological Laboratory in Sweden to investigate the presence of specific IgM and IgG antibodies to C. burnetii and R. conorii in patient sera.