Emerging rickettsioses in Northeast India.

Background: In India, rickettsial infections were first reported from Assam and West Bengal lay back during 1947. Since then, sporadic cases have been reported from different parts of the country except in the north eastern (NE) states. However, after a gap of 68 years, scrub typhus was reported to resurge in three states of NE region in 2012. This long serenity may be due to lack of surveillance and low index of suspicion for scrub typhus and other rickettsial infections. Therefore, a two year study was undertaken to study the sero-epidemiology of rickettsial infections viz., Scrub typhus (ST), Spotted fever group rickettsia (SFGR) and typhus group rickettsia (TGR) in Northeast India. Methods & Materials: We investigated scrub typhus reporting areas of three states viz., Assam, Arunachal Pradesh and Nagaland during 2013-2014. About 908 human blood samples were collected from healthy volunteers with informed consent. All collected human sera were screened for antibodies against ST, SFGR and TGR using a four step indirect ELISA with respective antigens. A sample whose total net absorbance was = 1.000 was considered as sero-positive. Positive samples were further titrated using 1:100, 1:400, 1:1600 and 1:6400 sample dilutions. Results: Overall, 33.5% (305/908), 11.2% (102/908) and 3.9% (35/908) were found to be seropositive for ST, SFGR andTGRrespectively. Co-circulation of ST and SFGRwasfound in all the three states whereas TGR were detected in samples collected from Arunachal Pradesh only. People engaged in agricultural and forest sectors were predominantly affected with a higher male to female ratio. Rural setting and lack of hygiene was a notable feature in the affected areas. Conclusion: Our findings indicated a wide circulation of rickettsial infections in this region. This is also the first evidence of SFGR and TGR circulation in NE region of India. Continuous surveillance, understanding eco-epidemiology of these diseases and consideration of these agents for diagnosis of febrile illness by public health workers is warranted in future. [ABSTRACT FROM AUTHOR]