Abstract:
The work presented here investigates a number of important components in the
epidemiology of foot-and-mouth disease (FMD) at the wildlife-livestock interface along the
Kruger National Park (KNP) and its adjoining private and provincial nature reserves (APNR).
This epidemiological setting is unique and complex, mainly due to the presence of African
buffaloes (Syncerus caffer) persistently infected with the Southern African Territories (SAT)
strains of the FMD virus. Despite a great deal of experimentation and field research, FMD
transmission from both persistently- and acutely-infected buffaloes to cattle is still poorly
understood, although it is accepted that the two species have to be in close contact for it to
occur. And even then, ‘close contact’ is ill-defined. Comparisons of three intensive study
sites in the FMD protection zone, comprising both communally-farmed as well as smallholder
cattle rangelands, were conducted to better understand this livestock system and determine
livestock distribution patterns. This vast heterogeneous landscape of the FMD protection
zone follows a latitudinal gradient of both human density and rainfall (increasing from north
to south), which is reflected in similar gradients in cattle densities, the number of households
owning cattle, consumption patterns as well as herding practice, whilst inversely associated
with cattle sales and calf mortality rates. Distribution studies of the cattle in these study sites
revealed a dry season dependence on water, and contraction of home ranges around
preferred habitat during the warm wet season. Herding, or the lack thereof, was evident in daily activity budgets of these cattle. Interestingly, seasonal differences in stray buffalo
dispersal patterns were the inverse of their domestic counterparts, being condensed along
the fence line during the dry season. Stray buffalo events mainly consisted of single animals
or very small groups, predominated by adult bulls. Most of these animals were destroyed
soon after straying from the FMD infected zone, although some managed to move into areas
with unvaccinated cattle, especially along major river courses. Swift removal of stray
buffaloes from livestock areas is paramount, since recent outbreaks all share the
characteristic of stray buffaloes being reported roaming the outbreak-area over extended
periods (months) prior to an outbreak. Combining cattle and stray buffalo habitat suitability
estimates revealed areas likely to facilitate contact between these species, which was
mostly driven by cattle dispersal into those condensed areas along the fence and rivers more
suitable for stray buffaloes during the cool dry season. This is also the season when acute
infection with FMD is most likely in buffaloes. Yet, when adjusting cattle habitat suitability to
incorporate their density, the concentration of preferred habitat during the warm wet season
forms small pockets of high cattle density, amplifying contact risk with stray buffaloes in these
areas. Simulation of stray buffalo movements along a least cost path, which incorporates
fence permeability, is shown to be a useful visual aid to finding high-risk stray buffalo
movement corridors. Contact-risk models performed well in retrospectively identifying high
risk areas during recent outbreaks. These risk outputs have value in informing risk-based
surveillance and strategic vaccination programs as well as in the delineation of disease
control zones.
