Disease
Human Disease, in medicine , is any harmful change that interferes with the normal appearance, structure, or function of the body or any of its parts. Diseases have diverse causes, which can be classified into two broad groups: infectious and noninfectious. Infectious diseases can spread from one person to another and are caused by microscopic organisms that invade the body. Noninfectious diseases are not communicated from person to person and do not have, or are not known to involve, infectious agents. Some diseases, such as the common cold , are acute, coming on suddenly and lasting for no more than a few weeks. Other diseases, such as arthritis , are chronic, persisting for months or years, or recurring frequently. Infectious diseases are caused by microscopic organisms commonly called germs. Physicians refer to these disease-causing organisms as pathogens. Pathogens that infect humans include a wide variety of bacteria , viruses , fungi , protozoans , and parasitic worms. In addi