Host-parasite interactions in a fragmented landscape.

Theory suggests that habitat fragmentation should reduce the risk of being parasitised due to reduced size and increased isolation of the host population. It is predicted that a threshold host population size exists, below which parasites will not be able to persist. Small mammals were trapped and their ecto-parasites removed in 14 field margins of varying widths over 2 years in a highly fragmented agro-ecosystem. No evidence to suggest the presence of a threshold in parasite prevalence was found, which may be due to the high rate of host movement and transiency within the system. Contrary to expectation, the probability of infestation decreased with host abundance and the abundance of alternative hosts, suggesting a dilution effect. The relatively long life cycle of small mammal specialist tick and flea species present under the prevailing environmental conditions may have left the parasites unable to keep up with the rate of reproduction and dispersal of the host. It is important to consider changes in the behaviour of the host and the presence of alternative hosts when predicting the effects of habitat fragmentation on disease spread.

Bovine tuberculosis in southern African wildlife: a multi-species host-pathogen system.

This review examines the current situation of bovine tuberculosis (bTB) in southern African savannah systems, and uses theory on multi-species host-pathogen systems to suggest possible options for future research and management. In southern Africa, the buffalo (Syncerus caffer) and the Kafue lechwe [Marsh antelope] (Kobus leche) have been found to be maintenance hosts for this disease, but the importance of other host species is becoming apparent. The role of other host species in the maintenance and spread of the disease varies, depending on the spatial distribution and resource utilization patterns of the species, disease susceptibility, transmission modes and the ecology of both host(s) and vector(s). Future research needs to identify the pathogenicity of bTB in each of the host species, and the mechanisms and rates of inter- and intra-specific transmission among different species, in order to develop multi-host models to understand the development and spread of the disease.