Development and optimisation of a diagnostic IgG ELISA against Crimean-Congo Haemorrhagic Fever virus

Crimean-Congo Haemorrhagic Fever virus (CCHFv) is endemic in over 30 countries, primarily affecting Low- and Middle-Income Countries (LMICs) in Africa, the Balkans, the Middle East, and Asia, with an estimated 3 billion people at risk. The expanding geographic range of the tick host and the trade in infected but asymptomatic livestock are contributing to the spread of CCHFv. Unfortunately, there is currently no effective or recognised vaccine, and importantly, few recognised or commercial diagnostic assays for detecting and monitoring virus infection.

In our study, we developed and optimised a new diagnostic human IgG ELISA assay. We utilized flashBAC Ultra to optimise expression and purification of recombinant nucleoprotein (NP) from CCHFv using a novel insect cell line. From this we established protocols to produce high yields of CCHFv.NP antigen that minimised other contaminating proteins. The assay was developed to ensure that we used optimum antigen coating conditions, drying method, assay buffers and incubation times. Alongside, we have generated a novel positive antibody control for the assay using in silico humanisation from hybridomas isolated from CCHFv.NP-immunised mice.

The optimised assay was successfully used to screen a panel of serum samples identified as CCHFv-positive from Turkey, along with a wide range of negative serum samples.

As a result, we have produced a functional assay that is currently undergoing further evaluation in a range of laboratories, including plans for assessment in CCHFv endemic countries. Our aim is that this diagnostic ELISA for CCHFv exposure will be accessible to a broad range of laboratories, enabling them to conduct routine investigations, thus enhancing the efficiency of diagnosis and the subsequent management of infected patients. The ELISA will also be useful in screening patients for participation in future CCHFv vaccine trials and sero-surveillance studies to continue monitoring exposure to this important pathogen.