10 - Microorganisms and disease

Abstract

Some pathogenic microorganisms can actively invade the host tissue. This process is known as infection. In such cases, the organism multiplies and is released into the environment to infect other susceptible hosts. When the activity of such an infection causes a reaction in the host, it is termed as disease. Manifestation of an infection as a disease may result in stomach upsets, skin rashes, headache, pulmonary problems, muscular paralysis, blindness, encephalitis, arthritis and many other clinical conditions. The factors influencing the occurrence and the severity of the response of the disease vary with the particular pathogen involved and their portal of entry, but the most important determinants for many infections lie within the host itself. One of these determinants is the age of the host at the time of infection, with the young and old being particularly susceptible. Those people who have diminished host defenses—that is, they are immuno-compromised, like the transplant patients and AIDS sufferers—are also at a great risk of acquiring infections.