Reversed passive hemagglutination and inhibition with Rift Valley fever and Crimean-Congo hemorrhagic fever viruses.

Reversed passive hemagglutination (RPHA) tests were performed by coating glutaraldehyde-fixed and tannic acid-treated sheep erthrocytes with antibodies to Rift Valley fever (RVF) and Crimean-Congo hemorrhagic fever (CCHF) viruses. Cells coated with crude antibody, in the form of mouse immune ascitic fluid, reacted with high specificity and sensitivity in RPHA tests with live or inactivated virus antigens. In inhibition (RPHI) tests, RVF antibody titers in human and sheep sera were similar to those determined by hemagglutination inhibition test. RVF virus antigen could be detected in viremic sheep sera by the RPHA technique. RPHI antibody titers to CCHF virus in human and hare sera were similar to indirect immunofluorescence (IF) titers, but sheep and cattle sera with RPHI titers of 1:32 or less were negative in IF tests.