There are many factors that have the potential to influence the emergence of new infections. A common factor is the spillover event. In the case of this event a pathogen present in one reservoir population will spread the pathogen to a new host or reservoir. An example of this is animal to human contact. For example, Ebola is thought to have been transmitted to humans by a bat. Meaning that the bat was the first reservoir host and passed it to a human host, a new population. Additionally, opportunistic pathogens, mutations, evolution, and reassortment could possibly lead to a new kind of infection. An opportunistic pathogen has the ability to hang around the body for long periods of time and either will remain unharmful to the body or could
