Rift Valley fever (RVF) is a mosquito-borne zoonotic viral disease native to the African continent. Outbreaks tend to occur in the wet seasons, and can affect numerous mammalian species including African buffalo. It is debated how the virus survives the inter-epidemic period when it is not detected in mammalian populations, either in cryptic wildlife hosts or by vertical transmission in mosquito hosts. In chapters 1 and 2 of this dissertation I show that buffalo do become infected in the inter-epidemic period although that is not sufficient to maintain viral cycling in the system without additional mammalian hosts and high vertical transmission rates.
Bovine tuberculosis is an emerging disease in sub-Saharan Africa, first detected in Kruger National Park buffalo populations in 1990. African buffalo are a maintenance host for BTB in the ecosystem, and there has been detailed research about pathogen provenance and diversity, effects on the host and transmission dynamics. These studies have focused on a single invasive pathogen, BTB – despite the fact that buffalo act as hosts for a multitude of pathogens. Fundamental theory in community ecology and immunology suggests that parasites within a host should interact, by sharing resources, competing for resources or by altering the immune response. In chapter 3 I show that animals with BTB are more likely to become infected with RVF, more likely to show clinical signs and that the presence of BTB increases the size of RVF epidemics in African buffalo. In chapters 4 and 5 I demonstrate that one of the mechanisms underlying this pattern may be immune-mediated whereby animals with BTB have altered susceptibility to RVF. Understanding how emerging diseases, like BTB, may affect native host-pathogen or pathogen - pathogen interactions will help us understand the full impact that emerging diseases may have on an ecosystem.