Summary
Emerging diseases of animals pose great threats to the health of the world and could potentially cripple financial wellbeing, food security or environmental vigour. Recent history has demonstrated that factors inherent in our globalised civilisation will ensure that new diseases will continue to occur in humans, as well as in animals. Focus has been on macroscopic factors underlying disease emergence, including trade, husbandry changes and environmental damage, any of which can facilitate the transfer of a microorganism from one host species to another, with possibly deadly results. However, the events that occur at the microscopic level deserve attention. The author presents the sequence of events that a microbe undertakes as it moves from one species to another and the hurdles faced as it negotiates a new environment to perhaps cause disease.

Keywords
Commensals, Dissemination, Emerging diseases, Immune response, Pathogens, Shedding.