Efficacy of foot-and-mouth disease vaccination in goats and movement patterns of livestock amongst smallholder farmers in Mnisi, Bushbuckridge, South Africa

Abstract

Foot-and-mouth disease (FMD) is a transboundary animal disease that has a major impact on livestock production, regional and international trade and livelihoods of smallholder farmers in endemic settings. The disease is caused by infection with foot-and-mouth disease virus (FMDV), a single stranded RNA virus that affects cloven-hoofed livestock and wildlife. Goats are susceptible to infection with FMDV, but their role in the epidemiology of the disease and response to vaccination is poorly understood. In southern Africa, FMDV serotypes Southern African Territories (SAT) 1, 2 and 3 are known to be endemic. In this study, we described the clinical presentation of FMDV SAT1 in goats, the efficacy of an oil emulsion FMD vaccine against heterologous challenge with a pool of field SAT1 FMDVs and described the patterns of livestock movements among smallholder farmers within a section of the FMD protection zone of Mpumalanga Province, South Africa. For this study, forty FMD sero-negative goats (6-12 months of age) of mixed sexes obtained from the FMD free zone of the country were randomly allocated to one of five treatment groups: G1 full cattle dose (2 ml), G2 (0.67 ml), G3 (0.33 ml), G4 (0.16 ml) or G5 (unvaccinated placebo) control. Goats were vaccinated with an inactivated FMD vaccine containing FMDV serotype SAT1 on day 0 and revaccinated at day 20 post vaccination. Thereafter, thirty-four goats were challenged by tongue inoculation at day 41 post-vaccination using 104.57 50% tissue culture infective dose (TCID50) of a FMDV SAT1 pool. Animals were examined daily, and clinical signs were scored. Rectal temperatures were measured daily, with temperatures ≥40°C defined as fever. Clinical specimens (nasal, oral and rectal swabs) were collected on days 0, 2, 4 and 6 post challenge. Viral shedding was determined using reverse-transcriptase real-time PCR. A semi-structured questionnaire and focus group discussions employing participatory mapping and semi-structured interviews were conducted among smallholder goat farmers within three animal health wards in the Mnisi Tribal Authority, a communal farming area within the FMD protection zone with vaccination of Mpumalanga Province. All the five challenged unvaccinated control goats developed fever within 48 h post challenge with a median fever duration of 5 days. Two unchallenged reduced-dose vaccinated goats maintained as sentinels developed fever at 5 and 9 days in contact, with lesions appearing at 4 and 8 days. Goats presented with nasal discharges and oral mucosal lesions of the lips, and interdigital cleft lesions. The virus caused mild clinical signs and natural transmission to reduced-dose vaccinated in-contact goats occurred. None of the goats vaccinated with the full cattle dose developed secondary FMD lesions. Vaccinated groups had lower temperatures compared to the unvaccinated controls (P<0.001). Based on RT-PCR results, goats in the G5 (unvaccinated control) shed more virus compared to all groups except for G4 (P<0.05), while goats in the G1 (full dose) shed less virus than goats in the G4. The results suggest that the G2 (0.67 ml) dose of the vaccine is sufficient to reduce viral shedding after heterologous challenge with a FMDV SAT1 pool. The movement network study identified several FMD high-risk locations within the study area that can be used to prioritise vaccination programmes and targeted disease surveillance. The study further identified communities at high risk of disease occurrence that might play significant roles in disease spread to disease free areas. Four locations in the FMD free zone of the country (Nelspruit, Tzaneen, Barbertone and Leboeng) were identified as having connections with the movement of goats from the study area. Thulamahashe, a nearby town in Mpumalanga Province and Giyani in Limpopo were the two locations with high degree of cattle movement from the study area. Findings from this study further demonstrated that goats are moved without official movement permits to the FMD free zone of the country, with most farmers being unaware of the need to obtain official veterinary movement permits. These animal movements put the country at risk of FMD outbreaks within the free zone. Information gained from this study contributes to a greater understanding of the role of goats in the epidemiology of FMD in an endemic setting and their response to vaccination. This will provide an opportunity to facilitate FMD endemic countries within the Southern African Development Community (SADC) region and Africa in general to progressively reduce the impact of FMD.