The human body provides a suitable environment for the growth of many types of microorganism, including bacteria, viruses, fungi, yeasts, and protozoa. It may also become the host for animal parasites such as insects, worms, and flukes.
Microorganisms (microbes) exist all around us and can be transmitted from person to person in many ways: direct contact, inhalation of infected air, and consumption of contaminated food or water. Not all microorganisms cause disease; many types of bacteria exist on the skin surface or in the bowel without causing ill effects, while others cannot live either in or on the body.
Normally, the immune system protects the body from infection. Invading microbes are killed before they can multiply in sufficient numbers to cause serious disease. (See also Malignant and immune disease.)
TYPES OF INFECTING ORGANISM
A typical bacterium consists of a single cell with a protective wall. Some bacteria are aerobic (requiring oxygen) and are therefore more likely to infect surface areas such as the skin or respiratory tract. Others are anaerobic and multiply in oxygen-free surroundings such as the bowel or deep wounds. Bacteria can cause symptoms of disease in two principal ways: by releasing toxins that harm body cells and by provoking an inflammatory response in the infected tissues.
Viruses are smaller than bacteria and consist simply of a core of genetic material surrounded by a protein coat. A virus can multiply only in a living cell, by using the host tissue’s replicating material.
Protozoa are single-celled parasites and are slightly bigger than bacteria. Many protozoa live in the human intestine and are harmless. However, other types cause malaria, sleeping sickness, and dysentery.
INFESTATIONS
Invasion by parasites that live on the body (such as lice) or in the body (such as tapeworms) is known as infestation. Since the body lacks strong natural defences against infestation, antiparasitic treatment is necessary. Infestation is often associated with tropical climates and poor standards of hygiene.
WHAT CAN GO WRONG
Infectious diseases occur when the body is invaded by microbes. This may be caused by the body having little or no natural immunity to the invading organism, or the number of invading microbes being too great for the body’s 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, as occurs in AIDS (acquired immune deficiency syndrome).
Infections (such as childhood infectious diseases or those with flu-like symptoms) can cause generalized illness or they may affect a specific part of the body (as in wound infections). Some parts are more susceptible to infection than others – respiratory tract infections are relatively common, whereas bone and muscle infections are rare.
Some symptoms are the result of damage to body tissues by the infection, or by toxins released by the microbes. In other cases, the symptoms result from the body’s defence mechanisms.
Most bacterial and viral infections cause fever. Bacterial infections may also result in inflammation and pus in the affected area.
WHY DRUGS ARE USED
Treatment of an infection is necessary only when the type or severity of symptoms shows that the immune system has not overcome the infection.
Bacterial infection can be treated with antibiotic or antibacterial drugs. Some of these drugs kill the infecting bacteria, whereas others merely prevent them from multiplying.
Unnecessary use of antibiotics may result in the development of resistant bacteria.
Some antibiotics can be used to treat a broad range of infections, while others are effective against a particular type of bacterium or in a certain part of the body. Antibiotics are most commonly given by mouth, or by injection in severe infections, but they may be applied topically for a local action.
Antiviral drugs are used for severe viral infections that threaten body organs or survival. Antivirals may be used in topical preparations, given by mouth, or administered by injection, usually in hospital.
Other drugs used to fight infection include antiprotozoal drugs for protozoal infections such as malaria; antifungal drugs for infection by fungi and yeasts, including candida (thrush); and anthelmintics to eradicate worm and fluke infestations. Infestation by skin parasites is usually treated with the topical application of insecticides.
MAJOR DRUG GROUPS
· Antibiotics
· Drugs for meningitis
· Antibacterial drugs
· Drug treatment for leprosy
· Antituberculous drugs
· Antiviral drugs
· Vaccines and immunization
· Antiprotozoal drugs
· Antimalarial drugs
· Antifungal drugs
· Anthelmintic drugs
Antibiotics
One in six prescriptions that British doctors write every year is for antibiotics. These drugs are usually safe and effective in the treatment of bacterial disorders ranging from minor infections, like conjunctivitis, to life-threatening diseases like pneumonia, meningitis, and septicaemia. They are similar in function to the antibacterial drugs, but the early antibiotics all had a natural origin in moulds and fungi, although most are now synthesized.
Since the 1940s, when penicillin, was introduced, many different classes of antibiotics have been developed. Each one has a different chemical composition and is effective against a particular range of bacteria. None is effective against viral infections (see Antiviral drugs).
Some of the antibiotics 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. For a description of each common class of antibiotic, seeClasses of antibiotic.
WHY THEY ARE USED
We are surrounded by bacteria – in the air we breathe, on the mucous membranes of our mouth and nose, on our skin, and in our intestines – but we are protected, most of the time, by our immunological defences. When these break down, or when bacteria already present migrate to a vulnerable new site, or when harmful bacteria not usually present invade the body, infectious disease sets in.
The bacteria multiply uncontrollably, destroying tissue, releasing toxins, and, in some cases, threatening to spread via the bloodstream to such vital organs as the heart, brain, lungs, and kidneys. The symptoms of infectious disease vary widely, depending on the site of infection and type of bacteria.
Confronted with a sick person and suspecting a bacterial infection, the doctor identifies the organism causing the disease before prescribing any drug. However, tests to analyse blood, sputum, urine, stool, or pus usually take 24 hours or more. In the meantime, especially if the person is in discomfort or pain, the doctor usually makes a preliminary drug choice, based on an educated guess as to the causative organism. In starting this empirical treatment, as it is called, the doctor is guided by the site of the infection, the nature and severity of the symptoms, the likely source of infection, and the prevalence of any similar illnesses in the community at that time.
In such circumstances, pending laboratory identification of the trouble-making bacteria, the doctor may initially prescribe a broad-spectrum antibiotic, which is effective against a wide variety of bacteria. As soon as tests provide more exact information, the doctor may switch the person to the recommended antibiotic treatment for the identified bacteria. In some cases, more than one antibiotic is prescribed, to be sure of eliminating all strains of bacteria.
In most cases, antibiotics can be given by mouth. However, in serious infections when high blood levels of the drug are needed rapidly, or when a type of antibiotic is needed that cannot be given by mouth, the drug may be given by injection. Antibiotics are also included in topical preparations for localized skin, eye, and ear infections (see also Anti-infective skin preparations, and Drugs for ear disorders).
USES OF ANTIBIOTICS
The table here shows common drugs in each class of antibiotic used to treat infections in different parts of the body. (It is not intended as a guide to prescribing.) For comparison, some antibacterial drugs are included under “sulphonamides” and “Other drugs”.
HOW THEY WORK
Depending on the type of drug and the dosage, antibiotics are either bactericidal, killing organisms directly, or bacteriostatic, halting the multiplication of bacteria and enabling the body’s natural defences to overcome the remaining infection.
Penicillins and cephalosporins are bactericidal, destroying bacteria by preventing them from making normal cell walls; most other antibiotics act inside the bacteria by interfering with the chemical activities essential to their life cycle.
CLASSES OF ANTIBIOTIC
Penicillins First introduced in the 1940s, penicillins are still widely used to treat many common infections. Some are not effective when they are taken by mouth and therefore have to be given by injection in hospital. Unfortunately, certain strains of bacteria are resistant to penicillin treatment, and other drugs may have to be substituted.
Cephalosporins These broad-spectrum antibiotics, similar to the penicillins, are often used when penicillin treatment has proved ineffective. Some can be given by mouth, but others are given only by injection. About 10 per cent of people who are allergic to penicillins are also allergic to cephalosporins. Some cephalosporins can occasionally damage the kidneys, particularly if used with aminoglycosides.
Macrolides Erythromycin is the most common drug in this group. It is a broad-spectrum antibiotic that is often prescribed as an alternative to penicillins or cephalosporins. Erythromycin is also effective against certain diseases, such as Legionnaires’ disease (a rare type of pneumonia), that cannot be treated with other antibiotics. The main risk with erythromycin is that it can occasionally impair liver function.
Tetracyclines These have a broader spectrum of activity than other classes of antibiotic. However, increasing bacterial resistance (see Antibiotic resistance) has limited their use, but they are still widely prescribed. As well as being used for the treatment of infections, tetracyclines are also used in the long-term treatment of acne, although this application is probably not related to their antibacterial action. A major drawback to the use of tetracycline antibiotics in pregnant women and young children is that they are deposited in developing bones and teeth.
With the exception of doxycycline, drugs from this group are poorly absorbed through the intestines, and when given by mouth they have to be administered in high doses in order to reach effective levels in the blood. Such high doses increase the likelihood of diarrhoea as a side effect. The absorption of tetracyclines can be further reduced by interaction with calcium and other minerals. Drugs from this group should not therefore be taken with iron tablets or milk products.
Aminoglycosides These potent drugs are effective against a wide range of bacteria. They are not as widely used as some other antibiotics, however, since they have to be given by injection and have potentially serious side effects, especially on the kidneys and middle ear. Their use is therefore limited to hospital treatment of serious infections. They are often given with other antibiotics.
Lincosamides The lincosamide clindamycin is not commonly used because it is more likely than other antibiotics to cause serious disruption of bacterial activity in the bowel. It is reserved mainly for treating bone, joint, abdominal, and pelvic infections that do not respond well to other antibiotics. It is also used topically for acne and vaginal infections.
Quinolones This group of drugs consists of nalidixic acid and substances chemically related to it, including fluoroquinolones. Fluoroquinolones have a wide spectrum of activity. They are used to treat urinary infections and acute diarrhoeal diseases, including that caused by Salmonella, as well as in the treatment of enteric fever.
The absorption of quinolones is reduced by antacids containing magnesium and aluminium. Fluoroquinolones are generally well tolerated but may cause seizures in some people. These drugs are less frequently used in children because there is a theoretical risk of damage to the developing joints.
HOW THEY AFFECT YOU
Antibiotics stop most common types of infection within days. Because they do not relieve symptoms directly, your doctor may advise additional medication, such as analgesics, to relieve pain and fever until the antibiotics take effect.
It is important to complete the course of medication as prescribed, even if all your symptoms have disappeared. Failure to do this can lead to a resurgence of the infection in an antibiotic-resistant form (see Antibiotic resistance).
Most antibiotics used in the home do not cause any adverse effects if taken in the recommended dosage. In people who do experience adverse effects, nausea and diarrhoea are among the more common ones (see also individual drug profiles in Part 2). Some people may be hypersensitive to certain types of antibiotic, which can result in a variety of serious adverse effects.
ANTIBIOTIC RESISTANCE
The increasing use of antibiotics in the treatment of infection has led certain types of bacteria to become resistant to the effects of particular antibiotics. This resistance to the drug usually occurs when bacteria develop mechanisms of growth and reproduction that are not disrupted by the effects of the antibiotics. In other cases, bacteria produce enzymes that neutralize the antibiotics.
Antibiotic resistance may develop in a person during prolonged treatment when a drug has failed to eliminate the infection quickly. The resistant strain of bacteria is able to multiply, thereby prolonging the illness. It may also infect other people and result in the spread of resistant infection.
One particularly important example of a resistant strain of bacteria is methicillin-resistant Staphylococcus aureus (MRSA), which resists most antibiotics but can be treated with other drugs such as teicoplanin and vancomycin.
Doctors try to prevent the development of antibiotic resistance by selecting the drug that is most likely to eliminate the bacteria present in each individual case as quickly and as thoroughly as possible. Failure to complete a course of antibiotics that has been prescribed by your doctor increases the likelihood that the infection will recur in a resistant form.
RISKS AND SPECIAL PRECAUTIONS
Most antibiotics used for short periods outside a hospital setting are safe for most people. The most common risk, particularly with cephalosporins and penicillins, is anallergic reaction that causes a rash. Very rarely, the reaction may be severe, causing swelling of the throat and face, breathing difficulty, and circulatory collapse – a potentially fatal condition called anaphylactic shock. If you have an allergic reaction, the drug should be stopped and immediate medical advice sought. If you have had a previous allergic reaction to an antibiotic, all other drugs in that class and related classes should be avoided. It is therefore important to inform your doctor if you have previously suffered an adverse reaction to treatment with an antibiotic (with the exception of minor bowel disturbances).
Another risk of antibiotic treatment, especially if it is prolonged, is that the balance among microorganisms normally inhabiting 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 (thrush) in the mouth, vagina, or bowel, and an antifungal drug may be needed.
A rarer, but more serious, result of disruption of normal bacterial activity in the body is a disorder known as pseudomembranous colitis, in which bacteria (called Clostridium difficile) resistant to the antibiotic multiply in the bowel, causing violent, bloody diarrhoea. This potentially fatal disorder can occur with any antibiotic, but is most common with cephalosporins and clindamycin.
COMMON DRUGS
Aminoglycosides Amikacin, Gentamicin, Neomycin, Streptomycin, Tobramycin
Cephalosporins Cefaclor, Cefadroxil, Cefalexin, Cefixime, Cefpodoxime, Ceftazidime
Tetracyclines Doxycycline, Oxytetracycline, Tetracycline
Macrolides Azithromycin, Clarithromycin, Erythromycin
Penicillins Amoxicillin/co-amoxiclav, Benzylpenicillin, Co-fluampicil, Flucloxacillin, Phenoxymethylpenicillin, Piperacillin/tazobactam
Lincosamides Clindamycin
Other drugs Aztreonam, Chloramphenicol, Ciprofloxacin, Colistin, Fusidic acid, Imipenem, Levofloxacin, Linezolid, Metronidazole, Rifampicin, Teicoplanin, Trimethoprim, Vancomycin
Drugs for meningitis
Meningitis is inflammation of the meninges (the membranes surrounding the brain and spinal cord), and it can be caused by both bacteria and viruses. Bacterial meningitis can kill previously well individuals in a matter of hours.
If bacterial meningitis is suspected, intramuscular or intravenous antibiotics will be needed immediately, and admission to hospital is arranged.
In cases of bacterial meningitis caused by Haemophilus influenzae or Neisseria meningitidis, people who have been in contact with an infected person are advised to have a preventative course of antibiotics, usually rifampicin or ciprofloxacin.
Antibacterial drugs
This broad classification of drugs comprises agents that are similar to antibiotics in function but dissimilar in origin. The original antibiotics were derived from living organisms such as moulds and fungi. Antibacterials were developed from chemicals. The sulphonamides were the first drugs to be given for the treatment of bacterial infections, and they provided the mainstay of the treatment of infection before penicillin (the first antibiotic) became generally available. Increasing bacterial resistance and the development of antibiotics that are more effective and less toxic have reduced the use of sulphonamides.
WHY THEY ARE USED
Sulphonamides are less commonly used these days, and co-trimoxazole is reserved for rare cases of pneumonia in immunocompromised patients.
Trimethoprim is used for chest and urinary tract infections. The drug used to be combined with sulfamethoxazole as co-trimoxazole, but because of the side effects of sulfamethoxazole, trimethoprim on its own is usually preferred now.
Antibacterials for tuberculosis are discussed in antituberculous drugs. Others, sometimes classified as antimicrobials, include metronidazole, which is used for a variety of genital infections and some serious infections of the abdomen, pelvic region, heart, and central nervous system. Other antibacterials are used to treat urinary infections. These include nitrofurantoin and quinolones (see Classes of antibiotic) such as nalidixic acid, which can be used to cure or prevent recurrent infections. The quinolones are effective against a broad spectrum of bacteria. More potent relatives of nalidixic acid include norfloxacin, which is used to treat urinary tract infections, and ciprofloxacin, levofloxacin, and ofloxacin. These are all also used to treat many serious bacterial infections.
HOW THEY WORK
Most antibacterials function by preventing growth and multiplication of bacteria. For example, folic acid, a chemical necessary for the growth of bacteria, is produced within bacterial cells by an enzyme that acts on a chemical called para-aminobenzoic acid. Sulphonamides interfere with the release of the enzyme. This prevents folic acid from being formed. The bacterium is therefore unable to function properly and dies.
HOW THEY AFFECT YOU
Antibacterials usually take several days to eliminate bacteria. During this time your doctor may recommend additional medication to alleviate pain and fever. Possible side effects of sulphonamides include loss of appetite, nausea, a rash, and drowsiness.
RISKS AND SPECIAL PRECAUTIONS
Like antibiotics, most antibacterials can cause allergic reactions in susceptible people. Possible symptoms that should always be brought to your doctor’s attention include rashes and fever. If such symptoms occur, a change to another drug is likely to be necessary. Treatment with sulphonamides carries a number of serious but uncommon risks. Some drugs 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 sulphonamides may also occasionally damage the liver, they are not usually prescribed for people with impaired liver function. These drugs are also less frequently used in children because there is a theoretical risk of damage to the developing joints.
COMMON DRUGS
Quinolones Ciprofloxacin, Levofloxacin, Moxifloxacin, Nalidixic acid, Norfloxacin, Ofloxacin
Sulphonamides Co-trimoxazole, Sulfadiazine
Other drugs Clofazimine, Dapsone, Daptomycin, Linezolid, Metronidazole, Nitrofurantoin, Thalidomide, Tinidazole, Trimethoprim
Drug treatment for leprosy
Leprosy, also known as Hansen’s disease, is a bacterial infection caused by Mycobacterium leprae. It is rare in the United Kingdom but relatively common in parts of Africa, Asia, and Latin America.
Hansen’s disease progresses slowly, first affecting the peripheral nerves and causing loss of sensation in the hands and feet. This leads to frequent unnoticed injuries and consequent scarring. Later, the nerves of the face may also be affected.
Treatment involves the use of three drugs together to prevent resistance from developing. Usually, dapsone, rifampicin, and clofazimine will be given for at least two years. If one of these drugs cannot be used, a second-line drug (ofloxacin, minocycline, or clarithromycin) might be substituted. Complications during treatment may require use of prednisolone, aspirin, chloroquine, or even thalidomide.
Antituberculous drugs
Tuberculosis is an infectious bacterial disease acquired, often in childhood, by inhaling the tuberculosis bacilli that are present in the spray of a sneeze or cough from an actively infected person. It may also, rarely, be acquired from infected unpasteurized cow’s milk. The disease usually starts in a lung and takes one of two forms: primary or reactivated infection.
In 90 to 95 per cent of those with a primary infection, the body’s immune system suppresses the infection but does not kill the bacilli. They remain alive but dormant and may cause the reactivated form of the disease. After they are reactivated, the tuberculosis bacilli may spread via the lymphatic system and bloodstream throughout the body.
The first symptoms of primary infection may include a cough, fever, tiredness, night sweats, and weight loss. Tuberculosis is confirmed through clinical investigations, which may include a chest X-ray, isolation of the bacilli from the person’s sputum, and a positive reaction – localized inflammation – to a skin test (in which tuberculin – a protein extracted from tuberculosis bacilli – is injected into the skin).
The gradual emergence in adults of the destructive and progressive form of tuberculosis is caused by the reactivated infection. It occurs in 5 to 10 per cent of those who have had a previous primary infection. Another form, reinfection tuberculosis, occurs when someone with the dormant, primary form is reinfected. This type of tuberculosis is clinically identical to the reactivated form. Reactivation is more likely in people whose immune system is suppressed, such as the elderly, those taking corticosteroids or other immunosuppressants, and those with AIDS. Reactivation tuberculosis may be difficult to identify because the symptoms may start in any part of the body seeded with the bacilli. It is most often first seen in the upper lobes of the lung, and is frequently diagnosed after a chest X-ray. The early symptoms may be identical to those of primary infection: a cough, tiredness, night sweats, fever, and weight loss.
If it is left untreated, tuberculosis continues to destroy tissue, spreading throughout the body and eventually causing death. It was one of the most common causes of death in the United Kingdom until the 1940s, but the disease is now on the increase again worldwide. Vulnerable groups are the homeless and people who have suppressed immune systems.
WHY THEY ARE USED
A person diagnosed as having tuberculosis is likely to be treated with three or four antituberculous drugs. This helps to overcome the risk of drug-resistant strains of the bacilli emerging (see Antibiotic resistance).
The standard drug combination for the treatment of tuberculosis consists of rifampicin, isoniazid, and pyrazinamide. In areas where there is high prevalence of drug-resistant tuberculosis, or a large number of organisms is present, ethambutol may be added. However, other drugs may be substituted if the initial treatment fails or drug sensitivity tests indicate that the bacilli are resistant to these drugs.
The standard duration of treatment for a newly diagnosed tuberculosis infection is a six-month regimen as follows: isoniazid, rifampicin, and pyrazinamide (perhaps with ethambutol) daily for two months, followed by isoniazid and rifampicin daily for four months. The duration of treatment can be extended from nine months to up to two years in people at particular risk, such as those with a suppressed immune system or those in whom tuberculosis has infected the central nervous system.
Corticosteroids may be added to the treatment, if the patient does not have a suppressed immune system, to reduce the amount of tissue damage.
Both the number of drugs required and the long duration of treatment may make treatment difficult, particularly for those who are homeless. To help with this problem, supervised administration of treatment is available when required, both in the community and in hospital.
Tuberculosis in patients with HIV infection or AIDS is treated with the standard antituberculous drug regimen; but lifelong preventative treatment with isoniazid may be necessary.
HOW THEY WORK
Antituberculous drugs act in the same way as antibiotics, either by killing bacilli or preventing them from multiplying. (See also Antibiotics).
HOW THEY AFFECT YOU
The drugs start to combat the disease within days, but benefits are not usually noticeable for a few weeks. As the infection is eradicated, the body repairs the damage caused by the disease. Symptoms gradually subside, and appetite and general health improve.
RISKS AND SPECIAL PRECAUTIONS
Antituberculous drugs may cause nausea, vomiting, and abdominal pain and occasionally lead to serious allergic reactions. When this happens, another drug is substituted.
Rifampicin and isoniazid may affect liver function; isoniazid may adversely affect the nerves as well. Ethambutol can cause changes in colour vision. Dosage is carefully monitored, especially in children, the elderly, and those with reduced kidney function.
TUBERCULOSIS PREVENTION
A vaccine prepared from an artificially weakened strain of cattle tuberculosis bacteria can provide immunity from tuberculosis by provoking the development of natural resistance to the disease (see Vaccines and immunization). The BCG (Bacille Calmette-Guérin) vaccine is a form of tuberculosis bacillus that provokes the body’s immune response but does not cause the illness because it is not infectious. The vaccine is no longer given as part of the routine immunization schedule but is offered to certain high-risk groups, for example newborn babies in areas where there is a high rate of tuberculosis.
The vaccine is usually injected into the upper arm. A small pustule usually appears 6 to 12 weeks later, by which time the person can be considered immune.
COMMON DRUGS
Amikacin, Capreomycin, Ciprofloxacin, Clarithromycin, Cycloserine, Ethambutol, Isoniazid, Pyrazinamide, Rifabutin, Rifampicin, Streptomycin
Antiviral drugs
Viruses are simpler and smaller organisms than bacteria and are less able to sustain themselves. These organisms can survive and multiply only by penetrating body cells. Because viruses perform few functions independently, medicines that disrupt or halt their life cycle without harming human cells have been difficult to develop.
There are many different types of virus; and viral infections cause illnesses with various symptoms and degrees of severity. Common viral illnesses include the cold, influenza and flu-like illnesses, cold sores, and childhood diseases such as chickenpox, mumps, and measles. Throat infections, pneumonia, acute bronchitis, gastroenteritis, and meningitis are often, but not always, due to a virus.
Fortunately, the body’s natural defences are usually strong enough to overcome infections such as these, with drugs given to ease pain and lower fever. However, the more serious viral diseases, such as pneumonia and meningitis, need 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 antiviral drugs have little effect. Antiviral agents must be given early in the course of a viral infection. They may also be used prophylactically (as a preventative). Some viral infections can be prevented by vaccination.
WHY THEY ARE USED
Antiviral drugs are helpful in the treatment of various conditions caused by the herpes virus: cold sores, encephalitis, genital herpes, chickenpox, and shingles.
Aciclovir and penciclovir are applied topically to treat outbreaks of cold sores, herpes eye infections, and genital herpes. They can reduce the severity and duration of an outbreak, but they do not eliminate the infection permanently. Aciclovir, famciclovir, and valaciclovir are given by mouth or, under exceptional circumstances, by injection, to prevent chickenpox or severe, recurrent attacks of herpes virus infections in those people who are already weakened by other conditions.
Influenza may sometimes be prevented or treated using oseltamivir or zanamivir. Oseltamivir may also be used to treat the symptoms of influenza in at-risk people, such as those over 65 or people with respiratory diseases such as COPD (chronic obstructive pulmonary disease) or asthma, cardiovascular disease, kidney disease, immunosuppression, or diabetes mellitus.
The interferons are proteins produced by the body and involved in the immune response and cell function. Interferon alpha and beta are effective in reducing the activity of hepatitis B and hepatitis C. Lamivudine is also used to treat hepatitis B, and ribavirin is used for hepatitis C.
Ganciclovir is sometimes used for cytomegalovirus (CMV). Respiratory syncytial virus (RSV) has been treated with ribavirin, and prevented by palivizumab. Drug treatment for AIDS is discussed in Drugs for HIV and AIDS.
HOW THEY WORK
Some antivirals act by altering the building blocks for the cells’ genetic material (DNA), so that the virus cannot multiply. Others stop viruses multiplying by blocking enzyme activity within the host cell. Halting multiplication prevents the virus from spreading to uninfected cells and improves symptoms rapidly. However, in herpes infections, it does not eradicate the virus from the body. Infection may therefore flare up on another occasion.
HOW THEY AFFECT YOU
Topical antiviral drugs usually start to act immediately. Provided that 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. Antivirals given by mouth or injection can occasionally cause nausea and dizziness.
RISKS AND SPECIAL PRECAUTIONS
Because some of these drugs may affect the kidneys adversely, they are prescribed with caution to people with reduced kidney function. Some antivirals can adversely affect the activity of normal body cells, particularly those in the bone marrow. Idoxuridine is therefore available only for topical use.
COMMON DRUGS
Aciclovir, Amantadine, Cidofovir, Famciclovir, Foscarnet, Ganciclovir, Inosine pranobex, Oseltamivir, Palivizumab, Penciclovir, Ribavirin, Valaciclovir, Valganciclovir, Zanamivir, Zidovudine/lamivudine
See also Drugs for HIV
Vaccines and immunization
Many infectious diseases, including most of the common viral infections, occur only once during a person’s lifetime. The reason is that the antibodies produced in response to the disease remain afterwards, prepared to combat any future invasion by the infectious organisms. The duration of such immunity varies, but it can last a lifetime.
Protection against many infections can now be provided artificially by using vaccines derived from altered forms of the infecting organism. These vaccines stimulate the immune system in the same way as a genuine infection, and provide lasting, active immunity. Because each type of microbe stimulates the production of a specific antibody, a different vaccine must be given for each disease.
Another type of immunization, called passive immunization, relies on giving antibodies (see Immunoglobulins).
WHY THEY ARE USED
Some infectious diseases cannot be treated effectively or are potentially so serious that prevention is the best treatment. Routine immunization not only protects the individual but may gradually eradicate the disease completely, as is the case with smallpox.
Newborn babies receive antibodies for many diseases from their mothers, but this protection lasts only for about three months. Most children are vaccinated against common childhood infectious diseases. Additionally, travellers are advised to be vaccinated against diseases common in the areas they are visiting.
Effective lifelong immunization can sometimes be achieved by a single dose of the vaccine. However, in many cases, reinforcing doses (boosters) are needed later to maintain reliable immunity.
Vaccines do not provide immediate protection and it may be up to four weeks before full immunity develops. When immediate protection is needed, it may be necessary to establish passive immunity with immunoglobulins.
HOW THEY WORK
Vaccines provoke the immune system into creating antibodies that help the body to resist specific infectious diseases. Some vaccines (live vaccines) are made from artificially weakened forms of the disease-causing organism. Others rely on inactive (or killed) disease-causing organisms, or inactive derivatives of them. Whatever their type, all vaccines stimulate antibody production and establish active immunity.
HOW THEY AFFECT YOU
The degree of protection varies among different vaccines. Some provide reliable lifelong immunity; others may not give full protection against a disease, or the effects may last for as little as six months. Influenza vaccines usually protect only against the strains of virus causing the latest outbreaks of flu.
Any vaccine may cause side effects but 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.
RISKS AND SPECIAL PRECAUTIONS
Serious reactions are rare and, for most people, the risk is far outweighed by the protection given. A family or personal history of seizures is not necessarily a contraindication to immunization, but immunization may be delayed if the condition is unstable. Children with any infection more severe than a common cold will not be given any routine vaccination until they have recovered.
Live vaccines should not be given during pregnancy, because they may affect a developing baby, nor should they be given to people whose immune systems are weakened. Those taking high doses of corticosteroids are advised to delay vaccinations until the end of drug treatment.
The risk of high fever following the DTaP/IPV/Hib (combined diphtheria, tetanus, acellular pertussis, inactivated polio, and Haemophilus influenzae type b) vaccine can be reduced by giving paracetamol at the time of the vaccination. The pertussis vaccine may rarely cause a mild seizure, which is brief, usually associated with fever, and stops without treatment. Children who have experienced such seizures recover completely.
IMMUNOGLOBULINS
Antibodies, which can result from exposure to snake and insect venom as well as infectious disease, are found in the serum of the blood (the part remaining after the red cells and clotting agents are removed). The concentrated serum of people who have survived diseases or poisonous bites is called immunoglobulin. Given by injection, it creates passive immunity. Immunoglobulins may be obtained from human donors or extracted from horse blood following repeated doses of the toxin.
Because immunoglobulins do not stimulate the body to produce its own antibodies, continued protection requires repeated injections of immunoglobulins.
Adverse effects from immunoglobulins are uncommon. Some people are sensitive to horse globulins, and approximately a week after the injection they may experience a reaction known as serum sickness, in which they have fever, a rash, joint swelling, and pain. Serum sickness usually ends in a few days but should be reported to your doctor before any further immunization.
TRAVEL VACCINATIONS
These are not normally needed for travel to Western Europe, North America, Australia, or New Zealand (but you should make sure that your tetanus and polio boosters are up to date). Consult your doctor if you are visiting other destinations. Check that children travelling with you have had all the routine childhood vaccinations and any that are necessary for the areas you will be travelling in.
If you are visiting an area where there is yellow fever, an International Certificate of Vaccination will be needed. You may also need this certificate in the future. Many countries that you might want to visit require an International Certificate of Vaccination if you have already been to a country where yellow fever is present.
You are at risk of other infectious diseases in many parts of the world, and appropriate vaccinations are a wise precaution. For example, a zone called the “Meningitis Belt” runs in a wide band across Africa from the Sahara down to Kenya. Anyone intending to visit this zone should have the combined A, C, W135, and Y meningococcal vaccine. Visitors to Saudi Arabia, especially for the Hajj or Umrah pilgrimages, may also be required to have had the meningitis A, C, W135, and Y vaccine.
You may need extra vaccinations if you are backpacking or planning a lengthy stay. For example, hepatitis A vaccine would be sensible for anyone travelling to a developing country, but a long-stay traveller should consider having hepatitis B and BCG (tuberculosis) as well. Rabies vaccination is recommended to anyone travelling into remote areas.
All immunization should be completed well before departure as the vaccinations do not give instant protection (BCG needs 3 months), and some (for example, typhoid) need more than one dose to be effective.
The NHS has a website providing travel health advice ( www.nhs.uk/livewell/travelhealth), including vaccination advice as well as information about specific health hazards such as malaria.
TRAVEL IMMUNIZATION
The immunizations you will need before travelling depend on the part of the world you intend to visit, although some diseases can be contracted almost anywhere. Wherever you intend to go, make sure that you have been immunized against diphtheria, tetanus, and polio and have had boosters if necessary. Advice on immunization may change from time to time. Before you travel, you should therefore ask your doctor or travel clinic for the most up-to-date information. The recommendations given here are for adults; consult your doctor about travel immunizations for children.
Antiprotozoal drugs
Protozoa are single-celled organisms that are present in soil and water. They may be transmitted to or between humans via contaminated food or water, sexual contact, or insect bites. There are many types of protozoal infection, each of which causes a different disease, depending on the organism involved. Trichomoniasis, toxoplasmosis, cryptosporidium, giardiasis, and pneumocystis pneumonia are probably the most common protozoal infections seen in the United Kingdom. The rarer infections are usually contracted as a result of exposure to infection in another part of the world.
Many types of protozoa infect the bowel, causing diarrhoea and generalized symptoms of ill-health. Others may infect the genital tract or skin. Some protozoa 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, in some cases, prevent it from spreading to other people. Increased attention to hygiene is an important factor in controlling the spread of the disease.
A variety of medicines is used in the treatment of these diseases. Some, such as metronidazole and tetracycline, are also commonly used for their antibacterial action. Others, such as pentamidine, are rarely used except in treating specific protozoal infections.
HOW THEY AFFECT YOU
Protozoa are often difficult to eradicate from the body. Drug treatment may therefore need to be continued for several months in order to eliminate the infecting organisms completely and thus prevent recurrence of the disease. In addition, unpleasant side effects such as nausea, diarrhoea, and abdominal cramps are often unavoidable because of the limited choice of drugs and the need to maintain dosage levels that will effectively cure the disease. For detailed information on the risks and adverse effects of individual antiprotozoal drugs, consult the appropriate drug profile in Part 2 of the guide.
TYPES OF PROTOZOAL DISEASE
Amoebiasis (Entamoeba histolytica), or amoebic dysentery, is an infection of the bowel (and sometimes the liver and other organs) usually transmitted in contaminated food or water. Its major symptom is violent, sometimes bloody, diarrhoea. Treatment is with diloxanide, metronidazole, or tinidazole.
Balantidiasis (Balantidium coli) is an infection of the bowel, specifically the colon, that is usually transmitted through contact with infected pigs. Possible symptoms include diarrhoea and abdominal pain. Treatment of the infection is with tetracycline, metronidazole, or diodohydroxyquinoline.
Cryptosporidiosis (Cryptosporidium) affects the bowel (and occasionally the respiratory tract and bile ducts). Cryptosporidiosis is spread through contaminated food or water or by contact with animals or other humans. Symptoms include diarrhoea and abdominal pain. There are no specific drugs to treat it, but paromomycin, azithromycin, or eflornithine may be effective.
Giardiasis (Giardia lamblia), or lambliasis, affects the bowel and is usually transmitted in contaminated food or water; but it may also be spread by some types of sexual contact. Its major symptoms are generalized ill-health, diarrhoea, flatulence, and abdominal pain. Treatment is with mepacrine, metronidazole, or tinidazole.
Leishmaniasis (Leishmania) is a mainly tropical and subtropical disease caused by organisms spread through sandfly bites. It affects the mucous membranes of the mouth, nose, and throat and may, in its severe form, invade organs such as the liver. Treatment is with paromomycin, sodium stibogluconate, pentamidine, or amphotericin.
Pneumocystis pneumonia (Pneumocystis jiroveci) is a potentially fatal lung infection usually affecting only people with reduced resistance to infection, such as those who are HIV positive. Symptoms include fever, cough, breathlessness, and chest pain. Treatment is with drugs such as atovaquone, co-trimoxazole, pentamidine, and dapsone with trimethoprim.
Toxoplasmosis (Toxoplasma gondii) is usually spread via cat faeces or by eating undercooked meat. Although usually symptomless, toxoplasmosis may cause generalized ill-health, mild fever, and eye inflammation. Treatment is necessary only if the eyes are involved or the patient is immunosuppressed (such as in HIV). It may also pass from mother to baby during pregnancy, leading to severe disease in the fetus. Treatment is usually with pyrimethamine with sulfadiazine, or with azithromycin, clarithromycin, or clindamycin/spiramycin (during pregnancy).
Trichomoniasis (Trichomonas vaginalis) most often affects the vagina, causing irritation and an offensive discharge. In men, it may occur in the urethra. It is usually sexually transmitted. Treatment is with metronidazole or tinidazole.
Trypanosomiasis (Trypanosoma), or African trypanosomiasis (sleeping sickness), is spread by the tsetse fly and causes fever, swollen glands, and drowsiness. South American trypanosomiasis (Chagas’ disease) is spread by assassin bugs and causes inflammation, enlargement of internal organs, and infection of the brain. Sleeping sickness is treated with pentamidine, suramin, eflornithine, or melarsoprol. Chagas’ disease is treated with primaquine or nifurtimox.
Antimalarial drugs
Malaria is one of the main killing diseases in the tropics. It is most likely to affect people who live in or travel to such places.
The disease is caused by protozoa whose life cycle is far from simple. The malaria parasite, which is called Plasmodium, lives in and depends on the female Anopheles mosquito during one part of its life cycle. It lives in and depends on human beings during other parts of its life cycle.
Transferred to humans in the saliva of the female mosquito as she penetrates (“bites”) the skin, the malaria parasite enters the bloodstream and settles in the liver, where it multiplies asexually.
Following its stay in the liver, the parasite (or plasmodium) enters another phase of its life cycle, circulating in the bloodstream, penetrating and destroying red blood cells, and reproducing again. If the plasmodia then transfer back to a female Anopheles mosquito via another “bite”, they breed sexually, and are again ready to start a human infection.
Following the emergence of plasmodia from the liver, the symptoms of malaria occur: episodes of high fever and profuse sweating alternate with equally agonizing episodes of shivering and chills. One of the four strains of malaria (Plasmodium falciparum) can produce a single severe attack that can be fatal unless treated. The others cause recurrent attacks, sometimes extending over many years.
A number of drugs are available for prevention of malaria; the choice depends on the region in which the disease can be contracted and the resistance to the commonly used drugs. In most areas, Plasmodium falciparum is resistant to chloroquine (see Choice of drug). In all regions, four drugs are commonly used for treating malaria: quinine, mefloquine, Malarone (a brand-name drug containing the antimalarials proguanil with atovaquone), and Riamet (a brand-name drug containing the antimalarials artemether with lumefantrine).
CHOICE OF DRUG
The following list is for guidance only. Because prevalent strains of malaria change very rapidly, and the risk may vary in different areas and/or countries, you must always seek specific medical advice before travelling. The parts of the world in which malaria is prevalent, and travel to which may make antimalarial drug treatment advisable, can be divided into six zones. Due to drug resistance, specific antimalarials are recommended for each zone. They may include:
Zone 1 North Africa, the Middle East, and Central Asia Depends on specific location. Chloroquine plus proguanil in areas of chloroquine resistance.
Zone 2 Sub-Saharan Africa Mefloquine, doxycycline, or Malarone.
Zone 3 South Asia Mefloquine, or chloroquine with proguanil, or doxycycline, or Malarone.
Zone 4 Southeast Asia Mefloquine in high-risk areas, or chloroquine with proguanil; doxycycline or Malarone in meloquine-resistant areas.
Zone 5 Oceania Mefloquine, or doxycycline, or Malarone.
Zone 6 Central and South America Central America: chloroquine or proguanil. South America: mefloquine, or doxycycline, or Malarone in high-risk areas, or chloroquine with proguanil.
WHY THEY ARE USED
The medical response to malaria takes three forms: prevention, treatment of attacks, and the complete eradication of the plasmodia (radical cure).
For someone planning a trip to an area where malaria is prevalent, drugs are given that destroy the parasites as they enter the liver. This preventative treatment needs to start up to three weeks before departure and continue for 1–4 weeks after returning (the exact timings depend on the drugs taken).
Drugs such as mefloquine and Riamet can produce a radical cure but chloroquine does not. After chloroquine treatment of non-falciparum malaria, a 14- to 21-day course of primaquine is administered. The drug is highly effective in destroying plasmodia in the liver but is weak against plasmodia in the blood. Primaquine is recommended only after a person leaves the malarial area because of the high risk of reinfection.
HOW THEY WORK
Taken to prevent the disease, the drugs kill the plasmodia in the liver, preventing them from multiplying. Once plasmodia have multiplied, the same drugs may be used in higher doses to kill plasmodia that re-enter the bloodstream. If these drugs are not effective, primaquine may be used to destroy any plasmodia that are still present in the liver.
HOW THEY AFFECT YOU
The low doses of antimalarial drugs taken for prevention rarely produce noticeable effects. Drugs taken for an attack usually begin to relieve symptoms within a few hours. Most of them can cause nausea, vomiting, and diarrhoea. Quinine can cause disturbances in vision and hearing. Mefloquine can cause sleep disturbance, dizziness, and difficulties in coordination.
RISKS AND SPECIAL PRECAUTIONS
When drugs are given to prevent or cure malaria, the full course of treatment must be taken. No drugs give long-term protection; a new course of treatment is needed for each journey.
Most of these drugs do not produce severe adverse effects, but primaquine can cause the blood disorder haemolytic anaemia, particularly in people with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Blood tests are taken before treatment to identify susceptible individuals. Mefloquine is not prescribed for those who have had psychological disorders or seizures.
OTHER PROTECTIVE MEASURES
Because Plasmodium strains continually develop resistance to the available drugs, prevention using drugs is not absolutely reliable. Protection from mosquito bites is of the highest priority. Such protection includes the use of insect repellents and mosquito nets impregnated with permethrin insecticide, as well as covering any exposed skin after dark.
COMMON DRUGS
Drugs for prevention Chloroquine, Doxycycline, Mefloquine, Proguanil, Proguanil with atovaquone (Malarone)
Drugs for treatment Artemether with lumefantrine (Riamet), Chloroquine, Mefloquine, Primaquine, Proguanil with atovaquone (Malarone), Pyrimethamine with sulfadoxine, Quinine
Antifungal drugs
We are continually exposed to fungi but, 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. These include tinea pedis (athlete’s foot), tinea cruris (jock itch), tinea corporis (ringworm), and tinea capitis (scalp ringworm). Caused by a variety of organisms, they are 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 that 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 occur in people taking antibiotics or oral contraceptives, in pregnant women, or in those with diabetes or immune system disorders such as HIV.
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 very rare, but may be serious and prolonged.
Because antibiotics and other antibacterial drugs have no effect on fungi and yeasts, a different type of drug is needed. Drugs for fungal infections are either applied topically to treat minor infections of the skin, nails, and mucous membranes or given by mouth or injection to eliminate serious fungal infections of the internal organs and nails.
WHY THEY ARE USED
Drug treatment is necessary for most fungal infections since they rarely improve alone. Measures such as careful washing and drying of the affected areas may help, but they are not a substitute for antifungal drugs. The use of over-the-counter preparations to increase the acidity of the vagina is not usually effective except when accompanied by drug treatment.
Fungal infections of the skin and scalp are usually treated with a cream or shampoo. Drugs for vaginal thrush are most commonly applied in the form of vaginal pessaries or cream applied with a special applicator. For very severe or persistent vaginal infections, a short course of fluconazole or itraconazole may be given by mouth. Mouth infections are usually eliminated by lozenges dissolved in the mouth or an antifungal solution or gel applied to the affected areas. For severe or persistent nail infections, either griseofulvin or terbinafine are given by mouth until the infected nails have grown out.
In the rare cases of fungal infections of internal organs, such as the blood, the heart, or the brain, potent drugs such as fluconazole and itraconazole are given by mouth, or amphotericin and flucytosine are given by injection. These drugs pass into the bloodstream to fight the fungi.
CHOICE OF ANTIFUNGAL DRUG
The table here shows the range of uses for some antifungal drugs. The particular drug chosen in each case depends on the precise nature and site of the infection. The usual route of administration for each drug is also indicated.
HOW THEY WORK
Most antifungals alter the permeability of the fungal cell’s walls. Chemicals needed for cell life leak out and the fungal cell dies.
HOW THEY AFFECT YOU
The speed with which antifungals provide benefit varies with the type of infection. Most 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, which takes months. Systemic infections of the internal organs can take weeks to cure.
Antifungal drugs applied topically rarely cause side effects, although they may irritate the skin. However, treatment by mouth or injection for systemic and nail infections may produce more serious side effects. Amphotericin, injected in cases of life-threatening systemic infections, can cause potentially dangerous effects, including kidney damage.
COMMON DRUGS
Amorolfine, Amphotericin, Caspofungin, Clotrimazole, Econazole, Fluconazole, Flucytosine, Griseofulvin, Itraconazole, Ketoconazole, Miconazole, Nystatin, Terbinafine, Tioconazole, Voriconazole
Anthelmintic drugs
Anthelmintics are drugs 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 (see Types of infestation). 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. In some cases, such as hookworm, larvae 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 anaemia. Worms can also infest the bloodstream or lodge in the muscles or internal organs.
Many people have worms at some time during their life, especially during childhood; most worms can be effectively eliminated with anthelmintic drugs.
WHY THEY ARE USED
Most worms common in the United Kingdom cause only mild symptoms and usually do not pose a serious threat to general health. Anthelmintic drugs are usually necessary, however, because the body’s natural defences against infection are not effective against most worm infestations. Certain types of infestation must always be treated since they can cause serious complications. In some cases, such as threadworm infestation, doctors may recommend anthelmintic treatment for the whole family to prevent reinfection. If worms have invaded tissues and formed cysts, they may have to be removed surgically. Laxatives are given with some anthelmintics to hasten expulsion of worms from the bowel. Other drugs may be prescribed to ease symptoms or to compensate for any blood loss or nutritional deficiency.
TYPES OF INFESTATION
Threadworm (enterobiasis) The most common worm infection in the UK, especially among young children. The worm lives in the intestine but travels to the anus at night to lay eggs, causing itching; scratching leaves eggs on the fingers, usually under the fingernails. Sucking the fingers or eating food with unwashed hands often transfers these eggs to the mouth. Keeping the nails short; good hygiene, including washing the hands after using the toilet and before each meal; and an early morning bath to remove the eggs are important in eradicating the infection.
Drugs Mebendazole
All members of the household should be treated simultaneously.
Common roundworm (ascariasis) The most common worm infection worldwide. It is transmitted to humans in contaminated raw food or in soil. The worms are large, and they infect the intestine, which can be blocked by dense clusters of them.
Drugs Levamisole, mebendazole
Tropical threadworm (strongyloidiasis) Occurs in the tropics and southern Europe. The larvae from contaminated soil penetrate the skin, pass into the lungs, are swallowed, and pass into the gut.
Drugs Albendazole, tiabendazole, ivermectin
Whipworm (trichuriasis) Mainly occurs in tropical areas of the world as a result of eating contaminated raw vegetables. The worms infest the intestines.
Drug Mebendazole
Hookworm (uncinariasis) Mainly found in tropical areas. The worm larvae penetrate the skin and pass via the lymphatic system and bloodstream to the lungs. They then travel up the airways, are swallowed, and attach themselves to the intestinal wall, where they feed off the intestinal blood supply.
Drug Mebendazole
Pork roundworm (trichinosis) Transmitted in infected undercooked pork. Initially, the worms lodge in the intestines, but larvae may invade muscle to form cysts that are often resistant to drug treatment and may require surgery.
Drugs Mebendazole, tiabendazole
Toxocariasis (visceral larva migrans) Usually occurs as a result of eating soil or eating with fingers contaminated with dog or cat faeces. The eggs hatch in the intestine and may travel to the lungs, liver, kidney, brain, and eyes. Treatment is not always effective.
Drugs Mebendazole, tiabendazole, diethylcarbamazine
Creeping eruption (cutaneous larva migrans) Mainly occurs in tropical areas and coastal areas of the southeastern US as a result of skin contact with larvae from cat and dog faeces. Infestation is usually confined to the skin.
Drugs Tiabendazole, ivermectin, albendazole
Filariasis (including onchocerciasis and loiasis) Occurs in tropical areas only. It may affect the lymphatic system, blood, eyes, and skin. Infection by this group of worms is spread by the bites of insects that are carriers of worm larvae or eggs.
Drugs Diethylcarbamazine, ivermectin
Flukes Sheep liver fluke (fascioliasis) is indigenous to the UK. Infestation usually results from eating watercress grown in contaminated water. It mainly affects the liver and biliary tract. Other flukes only found abroad may infect the lungs, intestines, or blood.
Drug Praziquantel
Tapeworms (including beef, pork, fish, and dwarf tapeworms) Depending on the type, worms may be carried by cattle, pigs, or fish and transmitted to humans in undercooked meat. Most types affect the intestines. Larvae of the pork tapeworm may form cysts in muscle and other tissues.
Drugs Niclosamide, praziquantel
Hydatid disease (echinococciasis) The eggs are transmitted in dog faeces, and the larvae may form cysts over many years, commonly in the liver. Surgery is the usual treatment for cysts.
Drug Albendazole
Bilharzia (schistosomiasis) Occurs in polluted water in tropical areas. The larvae may be swallowed or penetrate the skin. Once inside the body, they migrate to the liver; adult worms live in the bladder.
Drug Praziquantel
HOW THEY WORK
The anthelmintic drugs act in several ways. Many of them kill or paralyse the worms, which pass out of the body in the faeces. Others, which act systemically, are used to treat infection in the tissues.
Many anthelmintics are specific for particular worms, and the doctor must identify the nature of the infection before selecting the most appropriate treatment (see Types of infestation). Most of the common intestinal infestations are easily treated, often with only one or two doses of the drug. However, tissue infections may require more prolonged treatment.
HOW THEY AFFECT YOU
Once the drug 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.
COMMON DRUGS
Albendazole, Diethylcarbamazine, Ivermectin, Levamisole, Mebendazole, Niclosamide, Praziquantel, Tiabendazole