Seroprevalence of scrub typhus infection in patients with pyrexia at some malaria clinics in three western provinces of Thailand

In Thailand, the epidemiological data on scrub typhus infection represents only "the tip of an iceberg" especially in malaria clinics where patients c ome to seek attention because of other febrile illnesses that may have init ial clinical signs that are indistinguishable from malaria. The objectives of this study were to determine the prevalence of antibody titers to Orient ia tsutsugamushi, and its various strains, among patients at some malaria c linics in three western provinces of Thailand. The. sample was represented by 200 patients from 6 malaria clinics in Ratchaburi, Petchaburi and Kancha naburi provinces between June and November, 1994. Blood specimens were coll ected with their consent. Immunofluorescent antibody assays (IFA) were used for measuring IgM and IgG antibody titers for scrub typhus infection. The results showed that the prevalence rate for scrub typhus infection (IgM and /or IgG titer greater than or equal to 50) was 59.50% (119 cases). The immu nofluorescent antibody response to various strains of O. tsutsugamushi show ed that co-infections with the Karp, the Gilliam and the Kato strains were the most common (found in 68.10% of cases). Geometric mean antibody titers (GMT) were highest for the Karp strain, followed by the Gilliam then Kato s trains. In conclusion, this study indicates that the prevalence rate of scr ub typhus is not rare in these areas.