Detection of human antibodies to Crimean-Congo haemorrhagic fever virus using expressed viral nucleocapsid protein.

Diagnosis of Crimean-Congo haemorrhagic fever (CCHF) virus infections is hampered by the problems of handling this human pathogen, which requires the highest levels of biological containment. Recombinant antigens were examined for their potential as non-hazardous diagnostic reagents. The nucleocapsid (N) gene of the Greek AP92 isolate of CCHF virus was sequenced from cloned PCR products and the open reading frame was identified by homology to the N protein of a Chinese isolate of CCHF virus. The N protein was expressed to high levels in a baculovirus expression system. Three N protein-derived peptides were expressed in Escherichia coli as fusions with glutathione S-transferase and the antigenicities of these proteins and the baculovirus-expressed protein were tested by ELISA. When tested with laboratory animal sera representing all seven serogroups of nairoviruses, the only reactive sera were those raised to CCHF virus (Greek, Nigerian and Chinese isolates) and, more weakly, Hazara virus. When tested with a panel of known positive and negative human sera, the baculovirus-expressed N protein, and the peptide derived from the central region of the N protein, proved to be the best for identifying CCHF virus-specific IgG.