**2.5 Disease and pest outbreaks on livestock and crops**

Several studies have shown that the impact of climate change on the transmission and geographical distribution of animal diseases will vary according to the ecosystem, the type of land use, disease-specific transmission dynamics, susceptibility of the populations at risk and sensitivity of the pathogen to temperature and humidity [3, 18]. Climate change is expected to alter transmission rates between hosts by affecting the survival of the pathogens or parasites or the intermediate vectors, but also by other, indirect, forces that may be hard to predict with accuracy. For example, a series of droughts in East Africa between 1993 and 1997 resulted in pastoral communities moving their cattle to graze in areas normally reserved for wildlife. This resulted in cattle infected with a mild lineage of rinderpest transmitting disease both to other cattle and to susceptible wildlife such as buffalo and impala, causing severe disease, and devastating certain populations [19].

Climate change is also expected to affect the abundance or distribution of hosts or the predators of vectors and influence patterns of disease in ways that cannot be predicted from the direct effects of climate change alone [20]. Climate change-related disturbances of ecological relationships, driven perhaps by agricultural changes, overgrazing, deforestation, construction of dams and loss of biodiversity, could give rise to new mixtures of different species/strains, thereby exposing hosts to novel pathogens and vectors and causing the emergence of new diseases [21].
