The numbers of microbial species that can infect human beings are shown to be 1415, of which 868 species (61%) are zoonotic. Since most of the emerging pathogens (75%) are originated from other animals, public health sectors should be vigilant against the emergence of new zoonotic diseases. Only 33% of zoonoses can spread from human to human after introduction into human population. Various factors such as human demography, ecological change, global transportation and climate change are responsible for the emergence of zoonoses. Even a slight change in the ecological niche where pathogenic organisms thrive would result in the increase of the incidence of the disease.