Cloning and expression of Rift Valley fever virus nucleocapsid (N) protein and evaluation of a N-protein based indirect ELISA for the detection of specific IgG and IgM antibodies in domestic ruminants
Serodiagnosis of Rift Valley fever (RVF) currently relies on the use of live or inactivated whole virus as antigens. The recombinant nucleocapsid (N) protein of RVF virus was tested for diagnostic applicability in an indirect enzyme-linked immunosorbent assay (I-ELISA), using sera from experimentally infected sheep (n = 128), vaccinated sheep (n = 240), and field-collected sera from sheep (n = 251), goats (n = 362) and cattle (n = 100). The N-protein based I-ELISA performed at least as good as VN and HI tests. In goat the diagnostic sensitivity (D-Sn) and specificity (D-Sp) of the I-ELISA was 100% when using the anti-species IgG conjugate. Using protein G as a detection system, the D-Sn and D-Sp in goats were 99.4% and 99.5%, in sheep field sera both 100%, in cattle 100% and 98.3%, respectively. The I-ELISA based on recombinant N-protein has the potential to complement the traditional assays for serodiagnosis of RVF. Advantages of the N-protein are its safety, stability and cost-effectiveness in use and production.The authors wish to thank the staff of the Cytokine Center (Utrecht University), Special Pathogens Unit (National Institute for Communicable Diseases) and Veterinary Faculty of the Eduardo Mondlane University for technical assistance in this study. The work was sponsored by the International Foundation for Science (IFS grant B/3212-1), Sweden and by a MacGillavry PhD Fellowship of the Royal Dutch Academy of Science (KNAW) and Utrecht University, The Netherlands
