Infections And Infestations

Infectious diseases occur when the body is invaded by microbes against which its natural defenses are ineffective. This may be because the body has little or no natural immunity to the infection in question, or because the number of invading microbes is too great for the immune system to overcome. Serious infections can occur when the immune system does not function properly or when a disease weakens or destroys the immune system. That is what happens in AIDS (acquired immune deficiency syndrome).

Infections can be generalized (such as flu-like viruses and childhood infectious diseases) or they may affect one part of the body (as in wound infections). Some parts of the body are more susceptible to infection than others: respiratory tract infections are relatively common, whereas infections of the bones and muscles are rare.

Symptoms and consequences depend on the infecting organism and the parts of the body affected. Some are the result of damage to body tissues by the infection, others may be caused by toxins released by the microbes. In many cases, symptoms are the result of the activity of the body's defense mechanisms. Most bacterial and viral infections cause fever. Infections may also cause inflammation and pus formation in the affected area.

Antibiotics

Usually safe and effective in the treatment of infections - ranging from minor problems like conjunctivitis to life threatening diseases like pneumonia, meningitis, and septicemia - the antibiotics have played a major role in broadening the horizons of modern medical treatment.

Many different classes of antibiotics have been developed since 1941, when the first antibiotic - penicillin - was introduced. Each has a different chemical composition and is usually effective against a particular range of bacteria. Some have a broad spectrum of activity against a wide variety of bacteria. Others are used in the treatment of infection by only a few specific organisms.

Depending on the type of medicament and the dosage, antibiotics are either bactericidal, killing organisms directly, or bacteriostatic, halting the multiplication of bacteria and enabling the body's natural defenses to overcome the remaining infection.

There are two main mechanisms of action: penicillins and cephalosporins destroy bacteria by preventing them from making normal cell walls; most other antibiotics act inside the bacteria, interfering with the chemical activities essential to their life cycle.

Antibiotics stop most common types of infection within days. Because they do not relieve symptoms directly, your physician may advise additional medication such as analgesics to relieve pain and fever until the antibiotics start to take effect. It is important to complete the course of medication as prescribed by your physician even if all symptoms seem to have disappeared. Failure to do this can lead to a resurgence of the infection in an antibiotic-resistant form.

Most antibiotics used in the home do not cause side effects if taken in the recommended dosage. But digestive disturbances such as nausea and diarrhea, and yeast infections in women are among the more common reactions. Some people may be sensitive to particular types of antibiotics, and this can lead to serious adverse reactions.

Most antibiotics prescribed for short periods outside a hospital setting are safe for the majority of people. The most common risk, particularly with penicillins and cephalosporins, is an allergic reaction, usually a rash or other skin eruption, but rarely a more serious reaction occurs. If this happens the medicament should be stopped and immediate medical advice sought. A previous allergic reaction to an antibiotic means that all other medicaments in that class and related classes should be avoided. It is therefore important to inform your physician if you have previously suffered an adverse reaction to treatment with an antibiotic medicament.

Another risk of antibiotic treatment, especially if it is prolonged, is that the balance among microorganisms that normally inhabit the body may be disturbed. In particular, antibiotics may destroy the bacteria that normally limit the growth of candida, a yeast that is often present in the body in small amounts. This can lead to overgrowth of candida (also known as thrush) in the mouth, vagina, or bowel. In such cases an antifungal medicament may need to be prescribed. A rarer, but more serious, consequence of disruption of normal bacterial activity in the body is a disorder called pseudo membranous colitis, in which an antibiotic-resistant bacterium multiplies in the bowel, causing violent bloody diarrhea. Although this potentially fatal disorder can occur with any antibiotic, it is most common with the lincosamides.

Antibiotics taken by mouth or injection must be metabolized in the liver and excreted by the kidneys. Therefore, like many medicaments, they should be prescribed with caution for those people who have reduced kidney or liver function.

Antibacterial medicaments

The use of prontosil and its metabolite sulfanilamide to treat serious bacterial infections in 1935 marked the beginning of the era of chemotherapy. Sulfanilamide and the other "sulfa medicaments" were known as antibacterials because they were chemical in origin and development. Penicillin and other later agents derived from botanical sources, particularly molds and fungi, were originally designated as antibiotics. This distinction has become less meaningful with time, and now sulfonamides and other antibacterials are generally included within the broad grouping of antibiotics.

Most antibacterials rid the body of bacteria by preventing the growth and multiplication of the organisms. Antibacterials usually take several days to eliminate bacteria. During this time your physician may recommend additional medication to alleviate pain and fever. Sulfonamides can cause loss of appetite, rash, nausea, and drowsiness.

Like antibiotics, most antibacterials can cause allergic reactions in susceptible people. Possible symptoms that should always be brought to your physician's attention include rashes and fever. If such a reaction occurs, a change to another medicament is likely to be necessary. Treatment with sulfonamides carries a number of risks, the most common being a variety of rashes and other allergic reactions. Some medicaments in this group can cause crystals to form in the kidneys, a risk that can be reduced by drinking adequate amounts of fluid during prolonged treatment. Because sulfonamides may also occasionally damage the liver, they are not usually prescribed for people with impaired liver function. There is also a slight risk of damage to bone marrow, lowering the production of white blood cells and increasing the chances of infection. Physicians therefore try to avoid prescribing sulfonamides for prolonged periods. Liver function and blood composition are often monitored during unavoidable long-term treatment.

Antituberculous medicaments

Tuberculosis is a contagious bacterial disease acquired, often in childhood, by inhaling the tuberculosis bacilli (long, tube-shaped bacteria) present in the spray caused by a sneeze or cough from someone who is actively infected. Starting in a lung, tuberculosis takes one of two forms: primary infection or reactivation infection.

In 90 to 95 percent of those with primary infection, the body's immune system renders the bacilli quiescent. They remain alive, however, and they may spread via the lymphatic system and the bloodstream throughout the body.

Aside from some scarring and inflammation of the lungs, almost the only indication of infection is a reaction to an injection of tuberculin, a sterile extraction from the tuberculosis bacilli. When this is injected into the skin, only those people who have been previously infected show a reaction. Preventive measures are then undertaken.

Reactivation tuberculosis (the gradual emergence of the destructive, progressive and sometimes fatal disease in adults) occurs in 5 to 10 percent of those with a primary infection when their bodily defensive mechanisms are reduced. A clinically identical form of the disease, called reinfection tuberculosis, occurs when someone with the dormant primary form of the disease is reinfected.

The symptoms of reactivation (or reinfection) tuberculosis can be deceiving, for the disease may start in any part of the body originally seeded with bacilli. The disease is most often first seen in the upper lobes of the lung, and it is often diagnosed after a chest X ray. The early symptoms, which appear gradually, commonly include generally poor health, loss of appetite and weight, recurrent fever, and cough. Reactivation tuberculosis occurs in adults, most often in people over age 70.

Antituberculous medicaments act either by directly killing the bacteria or by preventing them from multiplying.

Although the medicaments start to combat the disease within days, benefits of medicament treatment are not likely to be noticeable for a few weeks. As the infection is gradually eradicated, the body's healing processes repair the damage caused by the disease. Symptoms such as fever and coughing gradually subside, and weight is gained as appetite and general health improve.

Some antituberculous medicaments may cause adverse effects (nausea, vomiting, and abdominal pain), and they occasionally lead to serious allergic reactions. These are most likely to occur during the second month of treatment and may parallel the symptoms of the disease itself -fever and general ill health, for instance. When this happens, another medicament is substituted.

Some medicaments may affect liver function (rifampin and isoniazid); others may adversely affect the nerves (isoniazid). Ethambutol can cause changes in vision, and for this reason is not generally prescribed for young children because they are unable to report the warning symptoms. Isoniazid can cause pyridoxine deficiency, and this vitamin may be given with the medicament.

Because the occurrence of adverse effects is usually related to levels of the medicament in the bloodstream, dosage is carefully monitored. Special care is needed for children, the elderly, and those with reduced kidney function.

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