Evaluation of an indirect enzyme-linked immunosorbent assay based on recombinant Baculovirus-expressed Rift Valley Fever virus nucleoprotein as the diagnostic antigen

Authors: FABURAY, BONTO - Kansas State University; Wilson, William - Bill; SECKA, ARSS - West African Livestock Innovation Centre (WALIC); Drolet, Barbara; McVey, David; RICHT, JUERGEN - Kansas State University

Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2019
Publication Date: 9/24/2019
Citation: Faburay, B., Wilson, W.C., Secka, A., Drolet, B.S., McVey, D.S., Richt, J. 2019. Evaluation of an indirect enzyme-linked immunosorbent assay based on recombinant Baculovirus-expressed Rift Valley Fever virus nucleoprotein as the diagnostic antigen. Journal of Clinical Microbiology. 57(10):e01058-19. https://doi.org/10.1128/JCM.01058-19.
DOI: https://doi.org/10.1128/JCM.01058-19

Interpretive Summary: Global veterinary and public health threats demand the development of safe and accurate diagnostic tests for pathogens of increasing risk such as Rift Valley fever virus (RVFV). This study evaluated the use of a recombinant RVFV nucleoprotein (N) fas sero-diagnostic antigen in an indirect enzyme-linked immunosorbent assay (ELISA). This serological assay was evaluated using antisera from sheep and cattle experimentally infected with two genetically distinct wildtype RVFV strains, and sera of indigenous sheep and goat populations exposed to natural RVFV field infection in The Gambia. The high specificity and correlation with the virus neutralization test support the feasibility of using the recombinant RVFV N-based indirect ELISA to assess RVF seroprevalence in livestock in endemic and non-endemic areas. This is allows safe generation of a serological assay for antibodies to RVFV that can be lethal to humans in an non-endemic country such as the US.

Technical Abstract: The increasing risk of Rift Valley fever virus (RVFV) as a global veterinary and public health threat demands the development of safe and accurate diagnostic tests. The aim of this study was to assess the suitability of a baculovirus expression system to produce recombinant RVFV nucleoprotein (N) for use as sero-diagnostic antigen in an indirect enzyme-linked immunosorbent assay (ELISA). The ability of the recombinant N antigen to detect RVFV antibody responses was evaluated in ELISA format using antisera from sheep and cattle experimentally infected with two genetically distinct wildtype RVFV strains, and sera of indigenous sheep and goat populations exposed to natural RVFV field infection in The Gambia. The recombinant N exhibited specific reactivity with the N-specific monoclonal antibody and various hyperimmune sera from ruminants. The indirect ELISA detected N-specific antibody responses in animals with 100% sensitivity when compared to the plaque reduction neutralization test (6-21 days post infection); and 97% and 100% specificity in sheep and cattle, respectively. There was high correlation between the indirect N ELISA and the virus neutralization test for sheep (R2 = 0.75; 95% CI = 0.73 - 0.92) and cattle (R2 = 0.80; 95% CI = 0.67 - 0.97) sera; in addition, the N-specific ELISA detected a RVFV seroprevalence of 26.1% and 54.3% in indigenous sheep and goats, respectively, in The Gambia. The high specificity and correlation with the virus neutralization test support the feasibility of using the recombinant baculovirus-expressed RVFV N-based indirect ELISA to assess RVF seroprevalence in livestock in endemic and non-endemic areas.