Some of the diseases are spread when the agents

A study by Hirschberg, Montagne & Fauci (2004) indicates that one of the factors that cause the emergence of these diseases include processes that occur in nature. Nevertheless, most of these illnesses are due to human activities and daily interactions. Some of these human activities include an increase in population, relocation from rural to urban areas, conflicts, terrorism and destructive use of natural resources. The emerging disease is first introduced to the susceptible population then through interaction, the disease is spread amongst individuals, thus it is easily sustained in the population infecting more and more people (Yang & Kim 2005).

Some of the diseases are spread when the agents are passed on from animals to humans through a process referred to as zoonosis. Zoonosis mainly occurs when the human population increases and in turn occupies new environments, thus increasing the contact between humans and animals. This factor acts as a serious threat to humans being infected.

According to the study by Ungchusak, Auewarakul & Dowell (2005), one of the infectious diseases whose spreading and transmission has been caused by human activities through close interactions with chimpanzees is HIV/ AIDS. This was through the hunting of bushmeat in Africa. The infectious disease was then further spread across the world through sexual transmission, blood transfer, breastfeeding and infectious drug use.

An emerging disease that emerged due to natural and human activities is influenza (flu). This infection is frequently transferred between humans and agricultural animals. These animals which include ducks and pigs mostly act as the host for the influenza virus. The avian flu emerged more than 10 years ago in birds (Ungchusak, Auewarakul & Dowell 2005). However, it has not been directly passed to humans as the H1N1 (swine flu) which is transmitted to humans from pigs in 2009.