Introduction to Infectious Diseases

Infectious diseases are caused by pathogenic microorganisms, such as bacteria, viruses, parasites, or fungi. Most of these diseases can be transmitted directly or indirectly from one person to another. These diseases are normally classified in three categories: diseases which cause high levels of mortality; diseases which place on population heavy burden of disability; and diseases which owing to the rapid and unexpected nature of their spread can have serious global consequences. Many of the key factors that cause infectious diseases may not be under 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.