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Bacteria cause disease by secreting or excreting toxins (as in botulism), by producing toxins internally, which are released when the bacteria disintegrate (as in typhoid), or by inducing sensitivity to their antigenic properties (as in tuberculosis).
- Infectious Disease
Infectious disease is a process caused by an agent, often a...
- Infectious Disease
Pathogens are able to cause disease because of a finely tuned array of adaptations, including the ability to attach to appropriate cells, often mediated by specialized structures such as the pili on Gram-negative rods.
- Overview
- Categories of organisms
- Chlamydial organisms
infectious disease, in medicine, a process caused by an agent, often a type of microorganism, that impairs a person’s health. In many cases, infectious disease can be spread from person to person, either directly (e.g., via skin contact) or indirectly (e.g., via contaminated food or water).
An infectious disease can differ from simple infection, which is the invasion of and replication in the body by any of various agents—including bacteria, viruses, fungi, protozoans, and worms—as well as the reaction of tissues to their presence or to the toxins that they produce. When health is not altered, the process is called a subclinical infection. Thus, a person may be infected but not have an infectious disease. This principle is illustrated by the use of vaccines for the prevention of infectious diseases. For example, a virus such as that which causes measles may be attenuated (weakened) and used as an immunizing agent. The immunization is designed to produce a measles infection in the recipient but generally causes no discernible alteration in the state of health. It produces immunity to measles without producing a clinical illness (an infectious disease).
The most important barriers to invasion of the human host by infectious agents are the skin and mucous membranes (the tissues that line the nose, mouth, and upper respiratory tract). When these tissues have been broken or affected by earlier disease, invasion by infectious agents may occur. These infectious agents may produce a local infectious disease, such as boils, or may invade the bloodstream and be carried throughout the body, producing generalized bloodstream infection (septicemia) or localized infection at a distant site, such as meningitis (an infection of the coverings of the brain and spinal cord). Infectious agents swallowed in food and drink can attack the wall of the intestinal tract and cause local or general disease. The conjunctiva, which covers the front of the eye, may be penetrated by viruses that cause a local inflammation of the eye or that pass into the bloodstream and cause a severe general disease, such as smallpox. Infectious agents can enter the body through the genital tract, causing the acute inflammatory reaction of gonorrhea in the genital and pelvic organs or spreading out to attack almost any organ of the body with the more chronic and destructive lesions of syphilis. Even before birth, viruses and other infectious agents can pass through the placenta and attack developing cells, so that an infant may be diseased or deformed at birth.
From conception to death, humans are targets for attack by multitudes of other living organisms, all of them competing for a place in the common environment. The air people breathe, the soil they walk on, the waters and vegetation around them, the buildings they inhabit and work in, all can be populated with forms of life that are potentially dangerous. Domestic animals may harbour organisms that are a threat, and wildlife teems with agents of infection that can afflict humans with serious disease. However, the human body is not without defenses against these threats, for it is equipped with a comprehensive immune system that reacts quickly and specifically against disease organisms when they attack. Survival throughout the ages has depended largely on these reactions, which today are supplemented and strengthened through the use of medical drugs.
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The agents of infection can be divided into different groups on the basis of their size, biochemical characteristics, or manner in which they interact with the human host. The groups of organisms that cause infectious diseases are categorized as bacteria, viruses, fungi, and parasites.
Chlamydia are intracellular organisms found in many vertebrates, including birds and humans and other mammals. Clinical illnesses are caused by the species C. trachomatis, which is a frequent cause of genital infections in women. If an infant passes through an infected birth canal, it can produce disease of the eye (conjunctivitis) and pneumonia in the newborn. Young children sometimes develop ear infections, laryngitis, and upper respiratory tract disease from Chlamydia. Such infections can be treated with erythromycin.
Another chlamydial organism, Chlamydophila psittaci, produces psittacosis, a disease that results from exposure to the discharges of infected birds. The illness is characterized by high fever with chills, a slow heart rate, pneumonia, headache, weakness, fatigue, muscle pains, anorexia, nausea, and vomiting. The diagnosis is usually suspected if the patient has a history of exposure to birds. It is confirmed by blood tests. Mortality is rare, and specific antibiotic treatment is available.
Infection occurs when viruses, bacteria, or other microbes enter your body and begin to multiply. Disease, which typically happens in a small proportion of infected people, occurs when the cells in your body are damaged as a result of infection, and signs and symptoms of an illness appear.
- Madeline Drexler
- 2010
- 2010
Overview. Bacterial infections can spread between people, in airborne particles, through bug bites or through contaminated food, water or surfaces. What is a bacterial infection? Bacterial infections are any illness or condition caused by bacterial growth or poisons (toxins).
Aug 21, 2020 · Bacteria are microscopic pathogens that reproduce rapidly after entering the body. They can release toxins that damage tissues and cause illness. Doctors typically prescribe antibiotics...
Show details. Infectious agents and how they cause disease. Infectious disease can be devastating, and sometimes fatal, to the host. In this part of the chapter we will briefly examine the stages of infection, and the various types of infectious agents. Go to: 10-1. The course of an infection can be divided into several distinct phases.
