Evaluation of an Indirect Enzyme-Linked Immunosorbent Assay Based on Recombinant Baculovirus-Expressed Rift Valley Fever Virus Nucleoprotein as the Diagnostic Antigen

J Clin Microbiol. 2019 Sep 24;57(10):e01058-19. doi: 10.1128/JCM.01058-19. Print 2019 Oct.

Abstract

The increasing risk of Rift Valley fever virus (RVFV) infection 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 serodiagnostic 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 wild-type RVFV strains and sera from 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 serum samples from ruminants. The indirect ELISA detected N-specific antibody responses in animals with 100% sensitivity compared to the plaque reduction neutralization test (6 to 21 days postinfection) and with 97% and 100% specificity in sheep and cattle, respectively. There was a high level of correlation between the indirect N ELISA and the virus neutralization test for sheep sera (R 2 = 0.75; 95% confidence interval [CI] = 0.73 to 0.92) and cattle sera (R 2 = 0.80; 95% CI = 0.67 to 0.97); in addition, the N-specific ELISA detected RVFV seroprevalence levels 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 idea of the feasibility of using the recombinant baculovirus-expressed RVFV N-based indirect ELISA to assess RVFV seroprevalence in livestock in areas of endemicity and nonendemicity.

Keywords: ELISA; PRNT; Rift Valley fever virus; diagnostic test; livestock; nucleoprotein.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Antibodies, Viral / immunology
  • Antigens, Viral / immunology*
  • Baculoviridae / genetics
  • Enzyme-Linked Immunosorbent Assay*
  • Genetic Vectors / genetics
  • Immunoglobulin G / immunology
  • Livestock
  • Neutralization Tests
  • Nucleoproteins / genetics
  • Nucleoproteins / immunology*
  • Recombinant Proteins / genetics
  • Recombinant Proteins / immunology*
  • Rift Valley Fever / diagnosis*
  • Rift Valley Fever / immunology*
  • Rift Valley fever virus / immunology*
  • Sensitivity and Specificity
  • Sheep
  • Sheep Diseases / diagnosis
  • Sheep Diseases / immunology

Substances

  • Antibodies, Viral
  • Antigens, Viral
  • Immunoglobulin G
  • Nucleoproteins
  • Recombinant Proteins