The relationship between cellular immune response to foot-and-mouth disease virus Asia 1 and viral persistence in Indian cattle (Bosindicus).

Foot-and-mouth disease (FMD), the most contagious animal disease, is associated with persistent viral infection in ruminants, despite the induction of systemic immune response. The present study was performed to decipher the relation between the persistent FMD virus (FMDV) infection and cellular immune response in Indian cattle (Bosindicus) following experimental inoculation of FMDV Asia 1. Persistent viral infection (carriers) was detected by antigen capture RT-PCR on the oesophageal-pharyngeal fluid. Viral excretion was found to be intermittent and strongly variable among the persistently infected Indian cattle. Lymphocyte proliferative (LP) response, assessed as reactivity of peripheral blood mononuclear cells to FMDV Asia 1 antigen (Ag) was of low magnitude indicating a weak primary cellular immune response following infection. LP response to FMDV Ag was higher among the non-carriers than carriers of FMDV Asia 1. An enhanced LP response was associated with the lack of virus shedding in the OPF. The findings of this study are suggestive of relationship between cellular immune response and virus excretion during persistence of FMDV Asia 1 in infected cattle.

Immune response and viral persistence in Indian buffaloes (Bubalus bubalis) infected with foot-and-mouth disease virus serotype Asia 1.

Despite their potential role in the spread of foot-and-mouth disease (FMD), the immune response and viral persistence in FMD virus (FMDV)-infected Indian buffaloes (Bubalus bubalis) have been unexplored. We found similar kinetics of neutralizing antibody responses in the sera and secretory fluids of buffaloes following experimental FMDV Asia 1 infection, but the lymphocyte-proliferative response in infected buffaloes was of low magnitude. Despite inducing a significant systemic and secretory immune response, viral persistence seems to be a common outcome in buffaloes following FMDV Asia 1 infection, which is associated with a weak cellular immune response.

Enhanced mucosal immune response in cattle persistently infected with foot-and-mouth disease virus.

The mucosal immune response to foot-and-mouth disease virus (FMDV) type Asia 1 was examined in experimentally infected cattle by assaying antibodies by the virus-neutralizing test (VNT) and IgA ELISA in two secretory fluids, oesophageal pharyngeal fluid (OPF) and oro-nasal fluid (ONF). Out of 17 animals infected by the intradermo-lingual route, 12 became persistently infected (carriers), as defined by positive antigen capture RT-PCR reactions for FMDV RNA in OPF samples collected at 28 days or later after exposure. This proportion of carriers (71%) with FMDV Asia 1 is comparable to other serotypes of the virus. When the two groups were examined, the carriers and non-carriers showed no difference in the serum antibody titre until the end of the experiment at 182 days post-infection (DPI). However, despite an initial similarity significantly higher neutralizing antibody titres and FMDV-specific IgA response were detected among the carriers than the non-carriers in both of the secretory fluids. The response was higher and more stable in ONF compared to OPF. Thus, mucosal antibody assays have the potential to be used as a means of differentiating carrier from non-carrier cattle. Furthermore, the findings are consistent with the higher mucosal antibody response in carriers being an effect of persistent infection rather than the cause.