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.

Antiviral medicaments

A simpler and smaller organism than the bacterium, the virus is less able to sustain itself. It can survive and multiply only by penetrating body cells. Because the virus performs so few functions independently, medicines that disrupt or halt its life cycle without harming human cells have been difficult to develop.

There are many different types of viruses, and viral infections cause illnesses with various symptoms and degrees of severity. Common viral illnesses include the cold, influenza and flu-like illnesses, and the usual childhood diseases such as mumps and chicken pox. Throat infections, acute bronchitis, pneumonia, gastroenteritis, and meningitis are often, but not always, caused by a virus.

Fortunately, the body's natural defenses are usually strong enough to overcome infections such as these, with medicaments given to ease pain and lower fever. However, the more serious viral diseases, such as pneumonia and meningitis, require close medical supervision.

Another difficulty with viral infections is the speed with which the virus multiplies. By the time symptoms appear, the viruses are so numerous that medicaments may have little effect. Antiviral agents should be given early in the course of an infection or they may be used prophylactically, i.e., as a preventive. Some viral infections can be prevented by vaccination.

In recent years, a few medicaments have been introduced that are effective against certain viruses. Many antiviral medicaments, such as acyclovir, idoxuridine, trifluridine, and vidarabine, act by preventing the formation of viral genetic material (i.e., they inhibit viral DNA replication). Thus, the virus cannot multiply. Halting multiplication of the virus prevents its spread to uninfected cells and improves symptoms, but in the case of herpes infections does not completely eradicate the virus from the body. Infection may therefore flare up on another occasion.

Amantadine acts earlier in the influenza virus life cycle to prevent it from multiplying. This medicament is most effective as a prophylactic, given before the infection has started.

Topical antiviral medicaments do not begin to act at once, but if the treatment is applied early enough, an outbreak of herpes can be cut short. Symptoms usually clear up within two to four days. Antiviral ointments may cause irritation and redness. Antiviral medicaments given by mouth or injection can occasionally cause nausea and dizziness.

Because some of these medicaments are excreted by the kidneys, they are prescribed with caution for people with reduced kidney function. Some antiviral medicaments can adversely affect the activity of normal body cells, particularly those in the bone marrow. Idoxuridine is for this reason available only for topical application.

Vaccines and immunization

Many infectious diseases, including most of the common viral infections, occur only once during a person's lifetime. The reason for this is that the antibodies produced in response to the disease remain afterward, prepared to repel any future invasion as soon as the first infectious germs appear. The duration of such immunity varies, but it can last a lifetime.

Protection from many infections can now be provided artificially by the use of vaccines derived from altered forms of the infecting organism. These vaccines stimulate the immune system in the same way as a real infection, and provide lasting, active immunity. A different vaccine is given for each disease because each type of microbe stimulates the production of a specific antibody.

Another type of immunization, called passive immunization, relies on the introduction of antibodies from someone who has recovered from a particular infectious disease. The transfer is made by means of serum (a part of the blood) containing antibodies.

Vaccines provoke the immune system into creating antibodies that help the body to resist specific infectious diseases. Many vaccines are made from artificially weakened forms of the disease-causing germ (live vaccine). But these weak germs are nevertheless effective in stimulating sufficient growth of antibodies. Other vaccines rely on inactive (or killed) disease-causing germs, or inactive derivatives. But their effect on the immune system remains the same. Effective antibodies are created; active immunity is established.

The degree of protection varies among different vaccines. Some provide reliable lifelong immunity; others may not give full protection against a disease, and the effects may last for as little as six months. Any vaccine may cause side effects, but when these occur they are usually mild and soon disappear. The most common reactions are a red, slightly raised tender area at the site of injection, and a slight fever or a flu-like illness lasting for one or two days.

For most children, the risk of severe reactions with vaccines is far outweighed by the protection provided. Although there has been concern about a possible association of permanent neurologic disorder and pertussis (whooping cough) vaccine, there is no scientific evidence to support this concern. While the pertussis vaccine -usually given in the combined form with diphtheria and tetanus as DPT - may rarely cause a mild seizure, it is brief, usually associated with fever, and stops without treatment. Children who have experienced such seizures recover completely without neurologic or developmental problems. The risk of high fever following DPT can be reduced by giving acetaminophen at the time of vaccination. Children who have an infection more severe than a common cold will not be routinely vaccinated until they have recovered.

Live vaccines should not be given during pregnancy, since they can affect the developing baby, nor should they be given to people whose immune systems are weakened by disease or medicament therapy. It is also advisable for those taking corticosteroids to delay their vaccination until the end of medicament therapy.

Antiprotozoal medicaments

Protozoa, single-celled organisms that are often present in soil and may infect animals, can be transmitted to or between humans through contaminated food or water, sexual contact, or bites from insects. There are many types of protozoal infections, each causing a different disease, depending on the organism involved. Trichomoniasis, giardiasis, and pneumocystis pneumonia are probably the most common protozoal infections.

Many types of protozoa infect the bowel, causing diarrhea and generalized symptoms of ill health. Others may infect the genital tract or skin. Some may penetrate vital organs such as the lungs, brain, and liver. Prompt diagnosis and treatment are important in order to limit the spread of the infection within the body and to other individuals. In many cases, increased attention to hygiene is an important factor in controlling the spread of the disease.

A variety of medicaments are used in the treatment of these diseases. Some, such as metronidazole and tetracycline, are also used for their antibacterial action. Others, such as iodoquinol, are rarely used except in specific protozoal infections.

Protozoa are often difficult to eradicate from the body. Medication treatment may therefore need to be continued for months in order to eliminate the infecting organisms completely, and thus prevent recurrence of the disease. In addition, unpleasant side effects such as nausea, diarrhea, and abdominal cramps are often unavoidable because of the limited choice of medicaments and the need to maintain dosage levels that will effectively cure the disease.

Antimalarial medicaments

Of all the infectious diseases that afflict mankind, the one that causes more illness and more deaths worldwide is malaria.  Malaria is caused by single-cell protozoa whose life cycle is far from simple. A parasite, the malaria plasmodium, as it is called, lives in and depends on the female anopheles mosquito during one part of its life. It lives in and depends on human beings during other parts of its life cycle.

Transferred to man in the saliva of the mosquito as she penetrates ("bites") the skin, the malaria parasite enters the bloodstream and settles in the liver. Although no symptoms appear yet, the malaria parasite multiplies, asexually.

Following its stay in the liver, the parasite enters another phase of its life cycle, circulating in the bloodstream, penetrating and destroying red blood cells and reproducing again, the results this time including male and female forms of the parasite. If the sexual forms then transfer back to a female anopheles mosquito via another "bite," they breed once more (bisexually), and are again ready to start a human infection.

It is after the emergence from the liver, when the plasmodia are entering and rupturing the red blood cells, that malaria appears in its classic, symptomatic form: high fever and profuse sweating, alternating with equally agonizing episodes of shivering and chills. One strain of malaria (there are four) can produce a single severe attack, possibly fatal if untreated. The other forms of malaria cause recurrent attacks, sometimes extending over many years.

A number of medicaments are available for malaria, the choice depending on many factors, such as the region in which the disease may have been contracted.

Most antimalarial medicaments act by rapidly killing plasmodia in the bloodstream. Taken as a suppressive, the medicaments kill the plasmodia before they enter the liver, so stopping them from multiplying. Once the plasmodia have multiplied in the liver, the same medicaments given in higher doses kill the parasites that reenter the bloodstream.

The low doses of antimalarial medicaments taken to suppress the disease rarely cause noticeable effects. Medicaments taken for an attack usually begin to relieve symptoms within a few hours. Most of them can cause nausea, vomiting, and diarrhea. More seriously, quinine can produce giddiness, noises in the ear, and disturbances in vision and hearing.

When medicaments are given to suppress or cure malaria the full course of treatment must be taken. No medicaments give long-term protection: new treatment is needed for each journey. Because no medicament is effective against every type of malaria, a change of antimalarial medicament may be necessary when traveling from one malarial area to another where a different form of malaria may be prevalent.

Though most of these medicaments do not produce severe adverse effects, primaquine can cause the blood disorder hemolytic anemia, particularly in people with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Hence, blood tests are taken before treatment to identify susceptible individuals.

Antifungal medicaments

We are continually exposed to fungi -in the air we breathe, the food we eat, and the water we drink. Fortunately, most of them cannot live in the body, and few are harmful. But some can grow in the mouth, skin, hair, or nails, causing irritating or unsightly changes, and a few can cause serious and possibly fatal disease. The most common fungal infections are caused by the tinea group of infections. These include tinea pedis (athlete's foot), tinea cruris (jock itch), and tinea capitis (scalp ringworm). They are caused by a variety of organisms and may be spread by direct or indirect contact with infected humans or animals. Infection is encouraged by warm, moist conditions.

Problems may also result from the proliferation of a fungus normally present in the body; the most common example is excessive growth of candida, a yeast which causes thrush infection of the mouth, vagina, and bowel. It can also infect other organs if it spreads through the body via the bloodstream.

Overgrowth of candida may be provoked by diabetes, pregnancy, immune system disorders such as AIDS, treatment with antibiotics, or by taking oral contraceptives

Superficial fungal infections -those that attack only the outer layer of the skin and mucous membranes -are relatively common and, although irritating, do not usually present a threat to general health. Internal fungal infections -for example, of the lungs, heart, or other organs -are rare, but may be serious and prolonged.

Because antibiotics and other anti-bacterial medicaments have no effect on fungi and yeasts, a different type of medicament is needed. Medicaments for fungal infections are either applied topically to treat minor infections of the skin and mucous membranes or given by mouth or injection to eliminate serious fungal infections of the internal organs and nails.

Most of these medicaments alter the permeability of the fungal cell's walls. The chemicals essential for cell life leak out and the cell dies.

The speed with which antifungal medicaments provide benefit varies with the type of infection. Thrush and most other fungal or yeast infections of the skin, mouth, and vagina improve within a week. The condition of nails affected by fungal infections improves only when new nail growth occurs, and this takes many months. Systemic infections of the internal organs can take weeks to cure.

Antifungal medicaments applied topically rarely cause side effects, although they may irritate the skin. However, treatment by mouth or ingestion for systemic and nail infections may produce more serious side effects. Amphotericin B, injected in cases of life-threatening systemic infections, often causes unpleasant and potentially dangerous effects, notably a severe fever that may require other medicaments. Because this medicament may also cause kidney damage, sufferers need regular blood tests. Griseofulvin, given for persistent nail infections, carries a risk of liver damage. For this reason it is prescribed only when topical treatments have failed and nail damage is severe.

Anthelmintic medicaments

Anthelmintics are medicaments that are used to eliminate the many types of worm (helminths) that can enter the body and live there as parasites, producing a general weakness in some cases, and serious harm in others. The body may be host to many different worms. Most species spend part of their life cycle in another animal, and the infestation is often passed on to humans in food contaminated with the eggs or larvae. Some larvae, such as those of hookworm, enter the body through the skin. Larvae or adults may attach themselves to the intestinal wall and feed on the bowel contents; others feed off the intestinal blood supply, causing anemia. Worms can also infest the bloodstream or lodge in the muscles or organs.

Many people have worms at some time during their life, especially during childhood; most can be effectively eliminated with anthelmintic medicaments.

The anthelmintic medicaments act in several ways. Many of them kill or paralyze the worms, and they pass out of the body in the feces. Others, that act systemically, are used to treat infection in the tissues. Many anthelmintics are specific for particular worms, and the physician must identify the worm before selecting the most appropriate treatment. Most common infestations of the intestine are easily treated, often with only one or two doses of the medicament. However, tissue infections may require more prolonged treatment.

Once the medicament has eliminated the worms, symptoms caused by infestation rapidly disappear. Taken as a single dose, or a short course, anthelmintics do not usually produce side effects. However, treatment can disturb the digestive system, causing abdominal pain, nausea, and vomiting.

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