Infectious diseases


A photograph of a young girl eating while standing behind a donkeyDiseases within animal populations are crossing into human populations with increasing frequency. Photo credit: WHOInfectious diseases are caused by pathogenic microorganisms, such as bacteria, viruses, parasites or fungi; the diseases can be spread, directly or indirectly, from one person to another. 

These diseases can be grouped in three categories: diseases which cause high levels of mortality; diseases which place on populations heavy burdens of disability; and diseases which owing to the rapid and unexpected nature of their spread can have serious global repercussions.

Many of the key determinants of health and the causes of infectious diseases lie outside the direct control of the health sector. Other sectors involved are those dealing with sanitation and water supply, environmental and climate change, education, agriculture, trade, tourism, transport, industrial development and housing.