Foot-and-mouth disease (FMD) vaccination and control in cattle at the wildlife/livestock interface of the Mnisi communal area

Abstract

Foot-and-mouth Diseases (FMD) is an important livestock disease with economic implications on trade. In southern Africa, the epidemiology of FMD is complicated as a result of the role of African buffalo (Syncerus caffer) in the maintenance and transmission of the South African Territories (SAT) virus serotypes. The aim of this study was to evaluate the FMD vaccination of cattle at the wildlife/livestock interface. A structured questionnaire was administered to communal farmers through in-person interview using the local language (Shangaan) to evaluate their perceptions concerning the current FMD vaccination programme. Cross-sectional sampling by cluster at herd levels was used to estimate proportions of cattle with high titres to FMDV-structural proteins, which was assumed to indicate an immunological response to vaccine routinely administered bi-annually in the absence of recently recorded outbreaks. A prospective cohort study was employed to evaluate immune responses and the duration of antibody responses to an inactivated aqueous trivalent FMD vaccine (SAT 1, SAT 2 & SAT 3) with blood samples collected on fortnightly bases. One hundred and four farmers responded to the questionnaire with 73% (76/104) being cattle owners while the remainder being hired cattle handlers. The majority of the respondents (79%; 95%CI: 70%-86%) indicated high level of satisfaction with the current animal health programme. The education level of the farmers varied over levels of satisfaction with the median education level being standard 9 (IQR: 2-12) for non-satisfied respondents, standard 3 (IQR: 0-6) for the little satisfied and standard 7 (IQR: 2-11) for the very satisfied respondents (P=0.036). Non-satisfied respondents were more likely to treat sick animals themselves than seek veterinary assistance (P=0.002). The majority of respondents identified the African buffalo as a risk factor for FMD outbreak (92%, 95%CI: 85%-96%). Two hundred and eighty-six cattle were sampled within six months post-vaccination and relative to antibody titre of ≥1.6 Log10 (1:40 dilution), 20% (95%CI: 14%-26%) of cattle had serologically converted to SAT 1, 39% (95%CI: 32%-46%) to SAT 2 and 22% (95%CI: 17%-27%) to SAT 3. Overall, only 4%, 15% and 9% of cattle had antibody titre ≥2 log10 to SAT 1, SAT 2 and SAT 3 respectively over a median period of 189 days since the most recent vaccination. Within the longitudinal study, few cattle had evidence of pre-existing antibody responses to SAT viruses at the beginning of the study. However, 14 days post-vaccination, the proportion of seropositive cattle (≥2 log10 titre) to the three SAT type viruses varied between 39% - 77% with SAT 2 having the highest proportions. Antibody responses peaked up to 98%, 98% and 65% at 42 days post-vaccination for SAT 2, SAT 3 and SAT 1 respectively until starting to decline at 56 days-post-vaccination.