Antibody responses induced by experimental West Nile virus infection with or without previous immunization with inactivated Japanese encephalitis vaccine in horses.

A group of horses immunized with inactivated Japanese encephalitis (JE) vaccine (JE-Immune Group) and a group of non-immunized horses (Non-Immune Group) were infected with West Nile virus (WNV). After WNV infection, neutralizing (Nt) antibody (Ab) titers to WNV were higher than those to JE virus (JEV) in the Non-Immune Group, but the NtAb titers to JEV were higher than those to WNV during most of the post-challenge observation period in the JE-Immune Group. Immunoglobulin M (IgM) Abs to WNV tested positive in the Non-Immune Group but negative in the JE-Immune Group, except for in one horse. These results suggest that diagnosis of WNV infection in JE-immunized horses requires serological tests for NtAb and IgM titers to both WNV and JEV.