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Foot-and-mouth disease (FMD) is a highly contagious viral disease which affects both domestic and wild biungulate species. This acute disease, caused by the FMD virus (FMDV), usually includes an active replication phase in the respiratory tract for up to 72 h postinfection, followed by hematogenous dissemination and vesicular lesions at oral and foot epithelia. The role of the early local adaptive immunity of the host in the outcome of the infection is not well understood. Here we report the kinetics of appearance of FMDV-specific antibody-secreting cells (ASC) in lymphoid organs along the respiratory tract and the spleen in cattle infected by aerosol exposure. While no responses were observed for up to 3 days postinfection (dpi), all animals developed FMDV-ASC in all the lymphoid organs studied at 4 dpi. Tracheobronchial lymph nodes were the most reactive organs at this time, and IgM was the predominant isotype, followed by IgG1. Numbers of FMDV-ASC were further augmented at 5 and 6 dpi, with an increasing prevalence in upper respiratory organs. Systemic antibody responses were slightly delayed compared with the local reaction. Also, IgM was the dominant isotype in serum at 5 dpi, coinciding with a sharp decrease of viral RNA detection in peripheral blood. These results indicate that following aerogenous administration, cattle develop a rapid and vigorous genuine local antibody response throughout the respiratory tract. Time course and isotype profiles indicate the presence of an efficient T cell-independent antibody response which drives the IgM-mediated virus clearance in cattle infected by FMDV aerosol exposure.

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PROCEEDINGSdeveloped, particularly for detecting the circulation of FMD virus in a subclinical form in FMD-vaccinated populations.When adapted for use in sheep, the 3ABC MAt-ELISA showed similar specificity, giving negative results with sera from vaccinated animals and positive in experimentally infected sheep that developed antibodies to FMDV structural proteins. In field conditions, the test was able to detect silent infections in asymptomatic sheep. However, there was more variation in antibody levels in naturally exposed animals than in experimental animals and not all sheep suspected to have been exposed to infection scored positive to 3ABC, (in spite of the detection of antibodies to sructural proteins) The failure to detect 3ABC induced antibodies in such animals could reflect a possible, individual immuno-tolerance to 3ABC, a poor sensitivity of the test, or the occurrence of a previous, unknown vaccination. Alternatively, the delayed onset and the shorter half-life of anti-3ABC antibodies with respect to antibodies against structural proteins should be considered.In conclusion, the demonstration of antibodies to 3ABC is conclusive evidence of FMD infection. Following extensive validation, the 3ABC MAt-ELISA is indicated to detect viral circulation in FMD-vaccinated populations, representing a valuable diagnostic tool for FMD eradication campaigns and control programs. For the application on a single animal further research is required, mainly in two directions: i) the correlation between 3ABC antibodies and the carrier status, ii) the immune response to both structural and non-structural FMDV proteins in sheep and other species following infection. ACKNOWLEDGEMENTS