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 I 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. (c) 2008 Elsevier B.V. All rights reserved.