Gelatin particle agglutination test for early serodiagnosis of Japanese spotted fever.

A gelatin particle agglutination (PA) test for Japanese spotted fever has been developed. Gelatin particles were sensitized with a sonicated causative rickettsia and used as antigens. The antibodies by PA test were detected as early as days 4-7 after the onset, whereas those by indirect immunoperoxidase (IP) test were detected after days 8-11. In addition, PA titers were higher than IP titers before days 20-23. The agglutinins detected by PA test were proven to be IgM because they were all sensitive to dithiothreitol. PA test was, however, less specific than IP test, giving a little nonspecific reaction to the sera from patients with scrub typhus and from individuals unrelated to those two rickettsioses. Nevertheless, PA test, which is simple, rapid, and easy to interpret the results, is useful for the early serodiagnosis of Japanese spotted fever.