Detection of Rift Valley fever virus antigen by enzyme-linked immunosorbent assay

Abstract

A double-antibody (sandwich) enzyme-linked immunosorbent assay (ELISA) was adapted to detect Rift Valley fever virus antigen. Antibodies were purified from hyperimmune mouse and rabbit sera by affinity chromatography, using CNBr-activated Sepharose 4B coupled to a .beta.-propiolactone-inactivated sucrose-acetone-extracted suckling mouse liver antigen. In the assay, antigen was captured by mouse antibody adsorbed to polystyrene plates and then detected by reacting sequentially with rabbit anti-Rift Valley fever virus antibody and swine anti-rabbit IgG conjugated to alkaline phosphatase. ELISA was useful in measuring viral antigen in different animal systems. Great variation was found in the amuont of antigen per PFU [plaque-forming unit] encountered in different circumstances. The ELISA system was optimized using supernatant fluids from infected Vero [African green monkey kidney] cell cultures and had a sensitivity of 105 PFU/ml. Hamsters developed progressive viremia much as seen in susceptible domestic animals, such as lambs; ELISA reliably detected 106 PFU/ml of viremic hamster serum. Rhesus monkeys with Rift Valley fever infection were positive by ELISA even when viremias were only 5 .times. 103 PFU/ml. ELISA was also useful in measuring viral antigen in infected mosquitoes.