Immunity to foot-and-mouth disease virus in guinea pigs: clinical and immune responses.

Clinical and immune responses were determined for guinea pigs infected with different doses of foot-and-mouth disease virus (FMDV) type A12, strain 119, administered by different routes. Vesicles developed on the tongue or heel pad 1 day after these areas were intradermally inoculated with FMDV. However, vesicles did not develop on the feet and tongue until 3 to 4 days after the intradermal inoculation of FMDV in the flank skin or after intracardiac or subcutaneous inoculation. Infected guinea pigs developed neutralizing antibody, immediate skin reactivity of the Arthus type (4 h), and delayed skin reactivity. In addition to a delayed skin response, the presence of a cell-mediated immune response to FMDV was shown by the specific production of macrophage migration inhibition factor by peritoneal exudate cells in response to FMDV. Kinetic studies showed that neutralizing antibodies were detected at 3 days postinfection, and Arthus and delayed skin reactivity were detected at 4 days postinfection. Some guinea pigs developed either mild or subclinical infections. Regardless of the dose of infectious virus, the route of inoculation, the severity of disease, or the time of clinical onset of disease, infected guinea pigs developed similar immune responses.