Development and evaluation of indirect antibody ELISA assay for early diagnosis and surveillance of Crimean-Congo hemorrhagic fever infection in humans.

Crimean-Congo hemorrhagic fever (CCHF) is an important tick borne zoonotic viral disease of humans. CCHF virus causes sporadic cases of severe illness across a huge geographic area across Africa to Europe to Asia including India. CCHF has emerged as a major public health concern in western Indian states including Gujarat and Rajasthan, where regular human cases were reported since the year 2011. Human serve as the dead-end host, and they gain infection via infected tick bite, in close contact with ruminants and from slaughter house. Currently, the detection of this fatal infection is limited to BSL-4 laboratory which is scarce even in developed economies. Thus, a safe, sensitive assay for early immunodiagnosis is crucial for disease management and containing the outbreak. In this study, the conserved recombinant nucleoprotein was exploited as a safe, scalable alternate antigen for development of indirect IgM and IgG ELISA detection platform. The indirect ELISA was evaluated using suspected clinical samples collected from hotspot areas in India. Comparison with reference MAC ELISA and IgG ELISA revealed a correlation of 95% and 100% respectively. The results indicate that the developed IgM and IgG indirect ELISA has high sensitivity and specificity for detecting CCHFV antibodies among human. These assays are easy to perform and can be employed for high throughput screening of human samples for clinical diagnosis as well as serosurveillance. These assays are also amenable for conversion to low-cost point of care testing formats for application in resource limited settings.