The Epidemiology of Rickettsial Infections in South India: Cohort Study

There is enough evidence to suggest that scrub typhus and spotted fever group rickettsioses are common causes of febrile illness in India. Serological evidence also exists for murine typhus, but is rarely tested for. Incidence, risk factors, clinical features and molecular epidemiology of these three infections are poorly understood. Delays in disease recognition and treatment may cause thousands of preventable deaths across India. The objectives of the research are to determine the incidence and risk factors of scrub typhus, spotted fever and murine typhus by severity, to determine clinical features of these neglected and often unrecognized infections. Further to study the effect of previous infection on incidence and severity of subsequent infections. Finally to study the association between vector parameters and scrub typhus risk. Enrolled will be 30,000 individuals who will be followed up for the development of fever using active and passive surveillance. Active surveillance will include household screening every 3-6 weeks. Fever cases occuring in the past two months will be tested for Scrub typhus, murine typhus and spotted fever IgG/IgM. 4000 individuals will be followed up by annual serological testing to identify asymptomatic infections. Participants notifying the study team with ongoing fever will undergo blood testing for acute diagnosis of rickettsial infection (IgM, PCR). In addition, we will enroll fever cases at study clinics who are not part of the main cohort. The research includes spatial and socio-economic risk factor analysis. Rodents carrying mite larvae will be trapped to compare the intensity of mite infestation between areas of high and low risk for human scrub typhus. The data on incidence, burden of disease and environmental determinants of scrub typhus, spotted fever and murine typhus will be used for health care planning and information campaigns for the public and medical professionals.