What is Disease?

Disease is defined as a condition that impairs of interferes with the well-being of an organism. The meaning of the term disease therefore involves a certain amount of individual judgment. One might justify calling all the conditions mentioned above diseases, but most people would not. Some diseases, like a nervous disorder or kidney stones, are caused by some breakdown in the normal processes of the body. Others result from pathogenic agents. But we’ll deal primarily with infectious diseases that are passed from one organism to another. These diseases are caused by pathogenic or disease-causing agents such as viruses, bacteria, and parasites. Diseases can also be caused by industrial chemicals or other foreign substances that enter the body. Asbestos fibers and a great many different chemicals, for example, have been shown to cause cancer.

For one thing, viruses or bacteria are said to be infectious when they can spread from person to person. Airborne infections, waterborne infections, and contact infections describe the most common ways infection spreads from one person to other. When a person has a cold or a sore throat, a sneeze or cough may discharge thousands of tiny droplets into the air. These droplets contain the disease-causing viruses or bacteria. This particular type of air borne infection is called a droplet infection. Waterborne infections usually spread most rapidly. This is especially true with viruses and bacteria associated with human body wastes. Many communities depend on underground water for their drinking water. It is becomes contaminated with sewage, groundwater can seep through the ground and spread disease, often many miles from the source of contamination.

Contact infections are slower in spreading disease. A person serving food in a restaurant can be a source of a contact infection. A contaminated fork is all that is needed to introduce pathogenic bacteria into the body. Sexual contact is another way viruses or bacteria can make contact with the body. People sometimes carry disease organisms in their bodies and yet are immune to the disease. These immune carriers present a problem. They do not suffer from the disease, but they are infectious. They can transfer the disease-causing agents to other people. Also, a person who recovers from a disease may be an immune carries for weeks, months, or even years without even realizing it. Because people in our society travel a lot, the disease can be spread over wide areas by immune carries.

Arthropods, insects and their relatives, are associated with certain infectious diseases. Houseflies carry disease organisms found in body wastes that they pick up on their feet and bodies. The flies spread the disease organisms when they get on food. Lice, fleas, ticks, and mosquitoes introduce pathogenic organisms directly into the body by penetrating the skin when they “bite”. If you have contact with disease-causing agents, it does not necessarily mean that you will become ill. Most pathogenic agents must enter the tissues of the body to cause an effect. The main way pathogenic organisms enter the body is through breaks or weaknesses in the mucous membranes that line the digestive and respiratory tracts. Airborne bacteria and viruses can easily enter the respiratory tract through these weaknesses. Food and water may also contain bacteria and viruses as well as parasites that can enter the digestive tract. Punctures, cuts, or scratches in the skin can introduce bacteria directly into the tissue.

M any bacteria secrete poisonous compounds called ‘exotoxins’. These poisons dissolve in the body fluid and eventually reach the blood stream. They are then distributed throughout the body and affect tissues some distance from the site of infection. For example, the spores of tetanus bacteria may enter our body if you step on a rusty nail. The spores become active in the muscle tissue. The resulting bacteria multiply and produce an exotoxin. Exotoxins may reach quite distant areas of the body, including the jaw muscles. Here the poison causes muscle spasms and paralysis. Because of this effect tetanus is commonly called lockjaw. In some cases, exotoxins are formed by bacteria in foods. These toxins formed outside the body produce food poisoning when the foods are eaten. The most deadly type of food poisoning is botulism. Like tetanus bacteria, botulism bacteria form spores. These spores may reach food before it is canned. If the food is not properly cooked and canned, the spores survive. When the food is sealed in an airtight can, the spores become active cells. These cells multiply and release exotoxins.

In the process of making exotoxins, a gas is produced by the bacteria. Often the gas causes the can to bulge, especially on the top. When the can is first opened, the gas sometimes makes a hissing sound as it escaped. Food from such cans should never be eaten. The poison is tasteless and odorless, but deadly. Botulism symptoms usually appear within 12 to 36 hours after the spoiled food is eaten. These symptoms include double vision, weakness, and paralysis that creeps from the neck to other body areas. Botulism is fatal in about 65 percent of the cases.

Other organisms that form toxins in foods include certain Salmonella and Staphylococcus bacteria. These types of food poisoning are more common but less deadly than botulism. Some bacteria form endotoxins. These poisons remain part of the bacteria and are released only when the bacterial cells die and break down. Endotoxins cause severe tissue reactions that may be fatal. Typhoid fever, tuberculosis, cholera, bubonic plague, and bacterial dysentery are endotoxin diseases.

Дата добавления: 2015-11-16