Essay on Deforestation

Infectious diseases have always been an important part of human life. They have significantly influenced human biology and society, even determining the course of major historical events.
Infectious diseases can be viewed ecologically as an extension of host–parasite relationships. They are as much a part of any ecosystem as predator–prey or plant–herbivore relationships. In fact, disease-causing viruses, bacteria and protozoans are commonly and collectively referred to as “microparasites” in infectious disease epidemiology. Moreover, infection by a microparasite is not inevitably a disease-causing event. Most often, host and microparasite coexist peacefully, because highly pathogenic genotypes that eliminate the host are selected against, as are susceptible hosts lacking acquired or native immunity (inherited resistance). Thus disease emergence is a transient phenomenon in a human population, and in its most severe form is typically a consequence of rapid social and environmental change or instability.

The first plague-causing pathogens such as smallpox are believed to have originated in tropical Asia early in the history of animal husbandry and large-scale forest clearing for permanent
cropland and human settlements (McNeil, 1976). Crowding and the mixing of people, domestic animals and wildlife, along with a warm humid climate, were as ideal for pathogen evolution, survival and transmission several millennia ago as they are now.

The concept of emerging infectious diseases (EIDs) was prompted by the appearance of novel pathogens such as human immunodeficiency virus (HIV) and Ebola virus; the evolution of more virulent or drug-resistant pathogenic variants of known microbes; and the geographic expansion and increasing epidemic outbreaks of the diseases caused by these pathogens as well as older diseases such as malaria and dengue. More recently, the concept was reinforced by the dramatic outbreak of severe acute respiratory syndrome (SARS) virus.

The...