Type-specific antigenicity of the U.S. isolates of RHDV. Liver homogenates from experimentally infected animals were tested by antigen-capture ELISA using type-specific HRP-conjugated monoclonal antibodies (MAb). MAb 1H8 is specific for the original RHDV serotype, MAb 3B12 is specific for the new RHDVa pandemic strain, and MAb 2B4 recognizes a shared epitope. The four U.S. RHDV isolates, Mexico 1989 isolate, an Italian isolate, and Korean isolate were compared in comparison with a control liver homogenate derived from an uninfected rabbit (Normal Liver). All U.S. isolates were recognized by MAb 3B12 as belonging to the RHDVa pandemic strain.