Diseases :: essays papers

Diseases Diseases are any harmful change that interferes with the normal appearance, structure, or function of the body or any of its parts. Since time immemorial, disease has played a role in the history of societies. It has affected and has been affected by economic conditions, wars, and natural disasters. An epidemic of influenza that swept the globe in 1918 killed between 20 million and 40 million people. Within a few months, more than 500,000 Americans died^more than were killed during World War I (1914-1918), World War II (1939-1945), the Korean War (1950-1953), and the Vietnam War (1959-1975) combined. Diseases have diverse causes, which can be classified into two broad groups: communicable and noncommunicable. Communicable diseases can spread from one person to another and are caused by microscopic organisms that invade the body. Noncommunicable 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, and come on suddenly and last for no more than a few weeks. Other diseases, such as arthritis, are chronic, consistent for months or years, or reoccur frequently. Every disease has certain characteristic effects on the body. Some of these effects, include fever, inflammation, pain, fatigue, dizziness, nausea, and rashes, are evident to the patient. These symptoms offer important clues that help doctors and other health care professionals make a diagnosis. Many times, the symptoms point to several possible disorders. In those cases, doctors rely on medical tests, such as blood examinations and X rays, to confirm the diagnosis. Communicable diseases are caused by microscopic organisms. 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. Also, it has been theorized that some proteins called prions may cause infectious diseases. Bacteria are microscopic single-celled organisms at least 1 micron long. Some bacteria species are harmless to humans, many are beneficial. But some are pathogens, including those that cause cholera, diphtheria, leprosy, plague, pneumonia, strep throat, tetanus, tuberculosis, and typhoid fever. The bacteria that are harmless and live in or on you are called resident bateria. Viruses are tens or hundreds of times smaller than bacteria. They are not cellular, but consist of a core of genetic material surrounded by a protective coat of protein. Viruses are able to survive and reproduce only in the living cells of a host. Once a virus invades a living cell, it directs the cell to make new virus particles. These new viruses are released into the surrounding tissues, and seek out new cells to infect.