Immunopathogenesis and pathology of experimental persistent infection with foot-and-mouth disease vims in cattle

In the present study, cattle were experimentally infected with foot-and-mouth disease virus Asia 1 to determine the pathological and immunological changes that occur in persistently infected animals (carriers) fbr better understand ing of pathogenesis. 15 out of the 23 cattle infected with FMDV Asia 1, developed persistent infection indicating that carrier state is the most common sequel following the infection. The serum neutralizing titres were significantly high following FMDV infection, but there was no significant difference between carriers and non-carriers. Interestingly secretory neutralizing titres of carriers were significantly higher than non-carriers. An enhanced lymphocyte (T-cell) stimulatory response 49 days after infection was associated with decline in the viral shedding which supported the role of cellular immune response in clearance of persistent infection. Histologically, lymphoid tissue of pharyngeal region, the site of viral persistence, showed many active follicles indicating lymphoprolifération. An absolute lack of cytopathological changes at this site favours the persistence of FMDV in presence of recognisable systemic and secretory immune response.