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A heavy infestation with the large roundworm Ascaris (15 to 35 cm long and about 0 allergy medicine nasal spray prescription paracort 20 mg order otc. A single worm may also migrate into the common bile duct and obstruct the passage of bile allergy attack paracort 40 mg purchase fast delivery. Often allergy symptoms vs infection cheap paracort 10 mg on-line, mechanical obstruction results not from the microorganism but from the inflammatory response of the host. In elephantiasis, an enormous swelling of limbs or the scrotum is caused when small worms, called filariae, become lodged in lymphatics. The worms stimulate a tissue reaction that occludes the vessels, causing swelling and tissue hypertrophy. Almost any duct or tubelike organ, thick or thin, can be obstructed during an infection, sometimes with life-threatening consequences. Inflammation of the epiglottis may impede the passage of air; infection of the meninges can cause hydrocephalus (a dilatation of the cerebral ventricles resulting from obstruction of the flow of cerebrospinal fluid); infection of the prostate can obstruct the flow of urine from the bladder; and an inflammatory reaction to the eggs of the liver fluke may result in severe disturbances of the portal circulation. Although the overexpression of the host response contributes greatly to the immediate signs and symptoms of disease, it also helps the host survive. This is illustrated by tuberculosis, a chronic disease that some patients live with for many years. The term has become defined more broadly now to describe a range of proteins that alter the normal metabolism of host cells with deleterious effects on the host. Knowledge of how toxins work fosters an understanding of the pathophysiology of many infectious diseases and, in some instances, reveals important information about normal cellular processes of the host. The role of many toxins in causing disease has been studied in detail and will be described in chapters on specific bacterial pathogens. Here, the discussion focuses on the basic concept of how bacterial toxins damage the host. Although many toxins have been associated with bacterial diseases, toxins have not been implicated as important components of diseases caused by fungi, protozoa, or worms. The host response is rarely so finely tuned that only the infection is controlled. In gonorrhea, the gonococci set off the host response, an inflammation that accompanies copious pus production (pus comprises the products of dead immune cells) and swelling and accounts for disease symptoms. Likewise, in many chronic infections, like tuberculosis, damage to tissues is caused by chronic inflammation. The host response to infection is often owing to both inflammation and the immune response. Both operate in acute and chronic diseases and can manifest either locally or systemically. The mechanisms involved in inflammation are discussed in detail in Chapter 6, and those involved in immunopathology are discussed in Chapter 7. The role of inflammation and the immune response on cell damage will be further emphasized in chapters on individual diseases, where they may occupy center stage. Examples of host responses to infection leading to harmful outcomes for the host include (1) the accentuated inflammatory response that places patients with a brain abscess at risk of dying, (2) the overwhelming activation of the complement system that kills patients suffering from septicemia, (3) an autoimmune response that causes rheumatic fever, and (4) cell-mediated immunity responsible for manifestations of chronic tuberculosis. In Toxins that Modulate Intracellular Targets Toxins that modulate intracellular targets modify host targets through covalent mechanisms. Exotoxins are organized into three distinct domains that can bind surface receptors and stimulate the translocation of a catalytic domain into the cytosol of the host cell. Occasionally, exotoxins are bound to the surface or synthesized in the cytoplasm of the bacterium and released on lysis of the cell. In contrast, many pathogenic bacteria, such as staphylococci, streptococci, pseudomonads, and bordetellae, make several toxins. In such multifactorial situations, the importance of any one toxin is difficult to assess. Toxins share with antibiotics an ambivalent position in the life of the pathogen that produces them. On the one hand, toxins are dispensable because they are not required for bacterial growth.
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Among their various activities allergy forecast redmond wa paracort 5 mg generic with visa, these cytokines mediate fever allergy medicine like allegra d 5 mg paracort cheap fast delivery, weight loss allergy grapes 5 mg paracort order with amex, and night sweats. In response to the carbohydrates, lipids, and proteins of the tubercle bacilli, macrophages also produce many other cytokines that modulate the immune response. This test involves the intradermal injection of proteins, or tuberculin, from tubercle bacilli. A positive reaction is indicated by thickening (induration) of the skin several days after inoculation, which results from infiltration by mononuclear phagocytes and T cells. This delayedtype hypersensitivity reaction recapitulates the local events that take place in the lung and other infected tissue. Depending on the site of the reaction, delayed-type hypersensitivity may account for diverse manifestations, such as pleurisy with effusion (the sometimes massive accumulation of exudate in the pleural cavities) or sudden inflammation of the meninges. Surprisingly few tubercle bacilli are present in the pleural fluid or cerebrospinal fluid during these infections, but they are able to cause considerable inflammation. The tuberculin skin test is most useful for diagnosing latent tuberculous infection. A newly positive test after a previous negative test (tuberculin conversion) indicates recent tuberculous infection and is an indication for chemoprophylaxis. Medical personnel who may have contact with infected patients are at increased risk of becoming infected and are regularly tested for skin test conversion. In some cases, this tuberculin negativity appears to Chapter 23: Mycobacteria: Tuberculosis and Leprosy 265 be specific for M. Soon after effective antituberculous therapy is initiated, the tuberculin test usually becomes positive as general overall health improves. Conversely, a false-positive tuberculin test may be caused by exposure to atypical mycobacteria, although in such cases the diameter of induration is usually small. Interferon Gamma Release Assays Given the limitations of the tuberculin skin test in diagnosing latent M. Interferon- plays a critical role in regulating the cellular immune response to M. Interferon- release assays are approved for every circumstance in which a tuberculin skin test would be used. Without cellular immunity and delayed-type hypersensitivity, caseous necrosis would not develop, but the tubercle bacilli would proliferate unchecked. Thus, the immune response contains the disease, even if it eventually causes damage. In fact, the body relies on two defensive strategies: the first involves the antimicrobial action of activated macrophages, and the second consists of walling off and containing the lesion by fibrosis and calcification. In short, defense mechanisms provide lifelong control of infection in most individuals. In contrast, active disease is usually diagnosed by acid-fast staining and culture of sputum or affected tissues. The initial diagnostic approach includes a careful history, direct examination of sputum or exudates, and a chest radiograph. Early morning sputa have the best yields because pulmonary secretions accumulate during sleep. Failure to diagnose and treat Pott disease can result in destruction of vertebrae and permanent disability. Less common manifestations include chronic inflammation of the meninges, pericardium, peritoneal cavity, or adrenal glands. If growth of tubercle bacilli occurs, it is important to test for antibiotic susceptibility. More sensitive nucleic acid amplification methods for rapid diagnosis are occasionally used in practice but have not replaced smear and culture. In any population of tubercle bacilli, chromosomal mutations associated with resistance to any single drug are already present in about one of every 106 to 107 bacteria, even though the organisms have never been exposed to the drug. Because tuberculous cavities can contain in excess of 1011 organisms, many of the bacteria present will be resistant to any single drug, even before treatment is begun. Fortunately, the chance that one organism will become resistant to two drugs simultaneously is small. Unfortunately, adherence with complex and prolonged treatment regimens is difficult.
Prevention has been successful for many serious epidemics allergy forecast corpus christi paracort 40 mg buy cheap on line, at least in the developed countries of the world allergy forecast long island ny buy paracort 20 mg amex. With the exception of vaccination allergy treatment kit 40 mg paracort purchase free shipping, most preventive measures involve improving sanitation and the standard of living, rather than employing medical procedures. Normal Microbiota the difference between endogenous and exogenous infections is sometimes quite sharp. However, in many other instances, the demarcation is less clear because it is difficult to define precisely which organisms constitute the normal microbiota (see Chapter 2). For example, some people harbor certain strains of virulent streptococci in their throat for a considerable period but only rarely come down with strep throat. The answer is yes if normal microbiota refers to organisms in or on the body that are not in the process of causing disease. The answer is no if this kind of streptococcus is considered not found in the throats of approximately 95% of all healthy people. No easy way exists out of this ambiguity, and the terms exogenous infection and endogenous infection must be used tentatively. Obviously, if we cannot define precisely the composition of normal microbiota, we cannot always distinguish between endogenous and exogenous infections. Another consideration that must also be kept in mind is that even for highly virulent microbes, exposure does not always lead to disease. For example, even at the height of deadly bubonic plague and typhus epidemics, most people were likely to have encountered the disease agent, but only about half the population became sick. Thus, human encounters with microbes are quite varied, and disease is not inevitable in every case. Humans display an idiosyncratic pattern of response to infectious agents; even within one individual, the pattern can change with age, nutritional state, and many other factors. Endogenously Acquired Diseases Endogenously acquired diseases are caused by agents present in or on the body. Members of the normal collection of microbes that are normally found on our skin or mucous membranes (our microbiota) may cause disease, usually when they penetrate into deeper tissues. Thus, a cut can lead to the production of pus caused by the staphylococci that inhabit healthy skin. The encounter with the agent took place long before the disease-namely, at the time the skin was colonized by the staphylococci. Colonization simply denotes the presence of microorganisms in a site of the body that may or may not lead to tissue damage and signs and symptoms of disease. It does suggest, however, that the microorganisms have invaded that site of the body and can multiply there. A schematic diagram showing the regions of the body in direct contact with the exterior. These include the outer aspects of the digestive, respiratory, and urogenital systems. The main systems that do not have such direct connections are the musculoskeletal, nervous, circulatory, and endocrine systems. In women, the genital tract is connected to the peritoneal cavity via the fallopian tubes. To enter the respiratory system, microorganisms face a series of aerodynamic and hydrodynamic obstacles. Microorganisms are inhaled in aerosol droplets or dust particles contained in the air we breathe. They take a circuitous path through the respiratory tract because they must navigate through complex anatomic structures such as nasal turbinates, the oropharynx, and the larynx. Accordingly, the surgical removal of the larynx (with its nooks and crannies) predisposes an individual to diseases of the lower respiratory tract. Microorganisms that arrive in the lower reaches of the respiratory tree face the powerful upward-sweeping action of the ciliary epithelium.