Detection of IgG antibody against Crimean-Congo haemorrhagic fever virus using ELISA with recombinant nucleoprotein antigens from genetically diverse strains.

Crimean-Congo haemorrhagic fever virus (CCHFV) has the propensity to cause nosocomial infections with a high fatality rate. Handling the virus requires biosafety level-4 facilities， limiting accessibility for many laboratories. Advances in molecular techniques have allowed preparation of safe recombinant antigens that have application in diagnosis and serosurveillance of CCHFV. The aim of this study was to determine genetic diversity in CCHFV based on all available complete sequence data for the S gene encoding CCHFV nucleoprotein (NP) and antibody cross-reactivity between the NP of a South African isolate and the NP of a Greek isolate (AP92)， the most genetically diverse CCHFV strain. The nucleotide sequence diversity and amino-acid diversity between genotypes， within genotypes and the pairwise distances were calculated for a dataset of 45 CCHFV isolates retrieved from GenBank. The most diverse virus， AP92， isolated from a tick in Greece， displayed the highest amino-acid difference (8·7%) with SPU415/85， isolated from a human infection in South Africa. Recombinant NP encoded for by codon-optimized S genes of SPU415/85 and AP92 were expressed in a bacterial host system and used to develop an in-house ELISA to detect IgG antibody against CCHFV in South African patients who survived infection. A total of 14/14 sera reacted with the South African recombinant NP and 13/14 reacted with the Greek recombinant NP. The serological cross-reactivity of the two NP antigens suggests that recombinant antigens prepared from geographically distinct CCHFV will have diagnostic and epidemiological applications worldwide.