Indirect hemagglutination test of Rickettsia orientalis: its specificity for reference strains, Karp, Gilliam and Kato.

Amberlite XE-64 and bovine serum albumin-treated rickettsia suspension, which was prepared from the chicken yolk sacs infected with each of 3 reference strains of Rickettsia orientalis, Karp, Gilliam and Kato, was sonicated at 10 KC for 15 min at 4 degrees C and centrifuged at 10,000 rpm for 40 min at 0 degrees C. The supernatant was used to sensitize the formalinized and tanned sheep red blood cells (SFTSRC). This antigen (2.5%) could be preserved for at least 1 wk at 4-8 degrees C and at least a month, if merthiolate (1:10,000) was added. Each SFTSRCP of 3 reference strains was found to be specific in indirect hemagglutination (IHA) reaction with each homologous immune serum and there was little cross reaction with the heterologous one. This minor cross reaction might be due to the presence of a small amount of soluble antigen in SFTSRC. No cross IHA reaction with the typhus fever immune serum was observed. The IHA test was considered to be useful for the diagnosis of scrub typhus.