Serological Evidence of Scrub Typhus in Mizoram, North Eastern Region of India

Objective: Differentiating scrub typhus from other acute febrile illnesses is difficult due to non-specificity of clinical symptoms and relative absence of eschar in Indian population. Antibody based serological tests are mainstay of scrub typhus diagnosis. To order to determine the performance of immunochromatography and IgM ELISA, immunochromatography and scrub typhus IgM ELISA were performed to detect the presence of antibodies against Onentia tsutsugamushi in acute serum of patients with acute febrile illness. Materials and Methods: A cross-sectional study was carried out in the Department of Microbiology, Civil Hospital Aizawl and Department of Microbiology, Civil Hospital Lunglei, Mizoram over a period of one year from October 1, 2018 to September 31, 2019. Serum samples from patients with acute febrile illness were processed for the detection of scrub typhus. A total of 253 samples were subjected to immunochromatography and IgM ELISA.Results: Using scrub typhus IgM ELISA as gold standard, the sensitivity, specificity and negative predictive value were calculated. Of the 253 serum samples tested, 36 were positive by both scrub typhus rapid test and IgM ELISA. 27 samples which were negative by scrub typhus rapid test reacted positive by IgM ELISA. 66 samples which were positive by scrub typhus rapid test were negative by IgM ELISA.Conclusion: Owing to the limitations of scrub typhus rapid test and immunfluorescence assay (IFA), commercially available recombinant IgM ELISA which has a good sensitivity and specificity may be an alternative in laboratories with moderate set up.