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Diseases, Disorders, and Other Problems - Infections and Infestations

 

PART SIX: Diseases, Disorders, and Other Problems - Infections and Infestations

Hoboken: John Wiley & Sons, Inc, 2004.

Infections are caused by organisms-including bacteria, viruses, fungi, and protozoa- that invade the body and multiply once they are inside. The course of an infection depends on several factors, including the nature of the infecting organism, its ability to cause disease, where it enters the body, how it spreads through the body, and the speed and effectiveness of the body's response to it. Disease-causing organisms require favorable conditions to cause infection-such as the right temperature, enough moisture, and a supply of nutrients. Viruses require suitable cells to invade and multiply in. 

 

 The immune system is a group of cells and proteins that can recognize foreign proteins (antigens) in the body, seek them out, and destroy them. The immune system attacks invading organisms either with white blood cells or proteins called antibodies. The immune system usually is able to mount an effective counterattack against invaders. The symptoms of an infection (such as fever, pain, and inflammation) are the results of this struggle. 

 

 Once infectious microbes enter your body, it takes time for them to multiply and cause symptoms. This period before symptoms develop is called the incubation period, which can vary from a few days to several months, depending on the particular disease-causing microbe. Doctors know the incubation periods for most common infectious diseases, making it possible to figure out when, where, and how a person acquired a particular infection. 

 

 After exposure to some kinds of organisms, the immune system is able to respond to future infections by those specific organisms and protect against them. Immunization is a way to induce this protective immune response without actually having the infection. Immunization can be active or passive. In active immunization, a person is given altered live or killed forms of a particular disease organism to trigger the same immune response that would occur from exposure to the actual organism. In passive immunization, a person is given injections of antibodies (infection- fighting proteins) produced by people who have recovered from an infection with a particular microbe. The antibodies are generally administered in a liquid derived from blood, called immunoglobulin. 

 

 Infections usually are limited to specific organs or tissues in which the infectious organisms are able to multiply. Some organisms are spread through the body in the lymphatic system-a circulatory system that is an important part of the immune system (see page 908). If disease organisms gain access to the bloodstream, they can cause a life-threatening infection that affects the whole body. 

 

 Some infectious organisms are spread when they are coughed or sneezed into the air and breathed in; others are spread through physical contact such as a handshake. Still other organisms are spread in contaminated food or water. Some microbes are transmitted to humans from animals or animal products (such as meat or eggs). If the spread of an organism that causes an infection can be stopped, the incidence of the disease may be reduced. 

 

 The parasites that cause infestations-such as worms, ticks, and lice-are larger than bacteria and viruses, and can be seen without a microscope. Infestations usually cause symptoms only at the site of infestation. 

 

 Generalized Infections 

 

 The infections in this section cannot be categorized easily, but one thing they have in common is that they produce symptoms throughout the body. Infectious mononucleosis and shingles are caused by viruses, while tetanus and toxic shock syndrome are caused by bacteria. 

 

 Infectious Mononucleosis 

 

 Infectious mononucleosis, often called mono for short, can be caused by either the Epstein-Barr virus or cytomegalovirus (see page 508). The infection can be transmitted from one person to another through oral contact such as kissing, and can spread to almost any organ. Mononucleosis is more common in teenagers and young adults (especially those who live in dormitories) and often occurs during stressful periods, such as during final examinations. 

 

 Symptoms 

 

 The early symptoms of infectious mononucleosis appear 4 to 6 weeks after exposure to the virus and resemble those of the flu (see page 649), including fever, headache, sore throat, swollen tonsils, and fatigue. Later symptoms may include painful, swollen glands in the neck, armpits, or groin (a condition called lymphadenopathy). Some people may also develop a rash over their entire body. In some cases, mono affects the liver and can cause jaundice (yellowing of the skin and the whites of the eyes; see page 785). If you have mono and you have a feeling of fullness in your upper left abdomen, you may have an enlarged spleen (an organ of the immune system that stores red blood cells and platelets). The symptoms of mono usually go away within 2 to 3 weeks, but you may continue to feel weak for a couple of weeks to several months. 

 

 Diagnosis 

 

 If you have flulike symptoms that persist for more than a week, especially if you have swollen glands, a sore throat, and fatigue, your doctor will take a detailed health history and order blood tests to check for an increased number of white blood cells (which fight infection) and antibodies (specific proteins the body produces to fight the virus). You may have a test in the doctor's office (called a mono spot test) that gives immediate results. If the test result is negative but the doctor still thinks you may have mono, he or she will recommend an antibody test to make a definite diagnosis. 

 

 Treatment 

 

 Because infectious mononucleosis is caused by a virus, doctors do not prescribe antibiotics to treat it. Getting plenty of rest is essential. Your doctor may recommend taking an over-the-counter pain reliever such as ibuprofen or acetaminophen. (Do not give aspirin to a child or adolescent who has a fever from any cause, because aspirin has been linked to Reye's syndrome, a potentially fatal condition; see page 411.) The doctor also will probably recommend drinking plenty of water, especially while you have a fever. In severe cases, a doctor may prescribe corticosteroids to control swelling in the throat and tonsils. If your spleen is enlarged, your doctor will recommend avoiding any activities that could cause injury, such as contact sports. An injury to your upper left abdomen could cause your spleen to rupture, which can be life-threatening. 

 

 Tetanus 

 

 Tetanus, also called lockjaw, is a potentially lifethreatening infection caused by clostridium bacteria that live in soil. The bacteria can enter the body through a cut in the skin that comes in contact with contaminated soil or through a wound caused by a contaminated object such as a nail or thorn. People who use drugs intravenously and share needles or who get tattoos or body piercings under unsanitary conditions are also at risk of infection. A toxin produced by the bacteria binds to the nerves in the spinal cord that control muscle activity and prevents them from functioning normally. 

 

 Symptoms 

 

 The symptoms of tetanus appear after an incubation period that can be as short as 3 days or longer than 3 weeks and can include headache, cramping and stiffness in the jaw (lockjaw), a stiff neck, and difficulty swallowing. Later symptoms include painful spasms and stiffness of the muscles in the neck, arms, legs, and stomach. Tetanus can affect the muscles involved in breathing, causing lifethreatening breathing problems. 

 

 Diagnosis and Treatment 

 

 If you have not had a tetanus shot within the past 10 years and you get a puncture wound, call your doctor or your local emergency number, or go to the nearest hospital emergency department to have the wound cleaned and examined to determine the appropriate treatment. 

 

 If tetanus develops, you will be hospitalized immediately and given antibiotics and an injection of tetanus antitoxin. You may also be given sedatives (such as benzodiazepines) or muscle relaxants to prevent muscle spasms. You may need a mechanical ventilator to help you breathe. The goal of treatment is to keep your body functioning for several weeks while the disease runs its course. In some cases, tetanus can be fatal. 

 

 Prevention 

 

 To help prevent tetanus, always clean small cuts with soap and water and apply an antiseptic to the wound. It is especially important to clean cuts that occur outdoors (where contamination with clostridium bacteria is more common) or puncture wounds (because they are hard to clean and provide an environment favorable to the growth of bacteria). 

 

 Infants are immunized against tetanus during their first year of life. Booster shots are recommended at 10-year intervals throughout life (see page 145). Make sure that each family member is immunized against tetanus and has a booster shot every 10 years; keep a record of the dates when family members received their shots. Because immunization against tetanus is routine, tetanus is rare in the United States, with fewer than 100 cases each year. 

 

 Shingles 

 

 Shingles is a condition caused by the reactivation of the varicella zoster virus (the virus that causes chickenpox; see page 439) and occurs mostly in older adults. During a chickenpox infection, the virus can invade the nerve cells in the brain stem or spinal cord and be inactive for years. If the virus is later reactivated, it can multiply, causing a rash of blisters and intense pain on the skin over the affected nerve. You cannot acquire shingles from contact with an infected person. However, if you have never had chickenpox, you can get chickenpox from a person who has shingles, because both conditions are caused by the same virus. 

 

 Shingles can affect almost any part of the body, but often affects one side of the trunk. The disorder can be serious if it affects the face or eyes, because it can cause temporary facial paralysis and impaired vision. It can also spread to the auditory nerves, resulting in hearing problems. In some cases, the pain from shingles persists after the blisters heal. This condition, called postherpetic neuralgia, can last weeks, months, or years. 

 

 A weakened immune system seems to play a part in reactivation of the virus. For this reason, people who have an impaired immune system, such as those who have an HIV infection or AIDS or who are being treated for cancer, are at increased risk of developing shingles. These people are also at increased risk of having recurring episodes of shingles. 

 

 Symptoms 

 

 The symptoms of shingles include an itchy, tingling feeling or severe, burning pain in the affected area several days before a rash develops. A person may also have a headache, fever, or chills. The rash, which usually appears in a band or patch, can be itchy or painful and is contagious to people who have never had chickenpox. After a few days, the rash turns into small, fluid-filled blisters, which gradually become encrusted and less contagious. The blisters usually disappear after about 7 days and, in most cases, do not leave scars. 

 

 Diagnosis and Treatment 

 

 Your doctor can diagnose shingles from your symptoms. Laboratory tests can confirm the diagnosis. 

 

 To treat shingles and reduce your risk of developing postherpetic neuralgia, your doctor will prescribe an antiviral medication, such as acyclovir, within 72 hours of the appearance of the rash. If your face is affected, your doctor will recommend steps you can take to protect your eyes. To relieve pain caused by postherpetic neuralgia, the doctor may prescribe an antidepressant (see page 712) or a topical medication such as lidocaine. Some doctors may prescribe corticosteroids to help reduce the risk of postherpetic neuralgia. 

 

 Toxic Shock Syndrome 

 

 Toxic shock syndrome is a rare condition that can develop when staphylococcal or streptococcal bacteria release toxins into the bloodstream. Toxic shock syndrome caused by staphylococcal bacteria was linked in the early 1980s to the use of superabsorbent tampons, which were then taken off the market. In rare cases, toxic shock syndrome can result when streptococcal bacteria (which are ordinarily found on the skin) infect a skin wound or surgical incision. Toxic shock syndrome, when severe, can lead to a life-threatening drop in blood pressure that, if not treated promptly, can lead to shock (see page 162) and be fatal. 

 

 Symptoms 

 

 Symptoms of toxic shock syndrome caused by staphylococcal bacteria appear suddenly and include high fever, vomiting and diarrhea, and a sunburnlike rash over the entire body. Other symptoms include bright red eyes and throat, headaches and muscle aches, and confusion. The rash may peel as it heals. 

 

 Symptoms of toxic shock syndrome caused by streptococcal bacteria usually appear 2 to 3 days after exposure to the bacteria. Symptoms of a skin infection caused by streptococcal bacteria include oozing pus from the site of the infection, and pain, redness, and a feeling of heat around the infected area. 

 

 If you have symptoms of toxic shock syndrome, call your doctor, 911 or your local emergency number, or go to the nearest hospital emergency department immediately. 

 

 Diagnosis 

 

 To diagnose toxic shock syndrome, a doctor takes a detailed health history and orders blood tests to check for abnormalities in the liver and kidneys and to rule out other possible illnesses. He or she may also test a sample of fluid from any pus-filled sores (boils) on the skin or infected cuts. 

 

 Treatment 

 

 Treatment for toxic shock syndrome requires a stay in a hospital. You will be given fluids intravenously (through a vein) and an antibiotic. Your blood pressure and the function of your liver, kidneys, and other vital organs will be closely monitored. If toxic shock syndrome is caused by a skin infection such as a boil or abscess, your doctor may drain the infected area. If toxic shock syndrome develops after surgery, a person will need to return to the hospital so the doctor can determine the cause and remove any dead tissue if necessary. 

 

 Infestations and Diseases Spread by Insect and Animal Bites 

 

 Infestations occur when parasites invade your body and live either on it (as lice do) or in it (as tapeworms do). Parasites that live on the skin usually cause no symptoms other than discomfort. Some parasites, such as ticks, can cause infections because they can carry disease-causing microorganisms. Parasites that live inside the body may go undetected because they sometimes cause vague symptoms that often go unnoticed. However, if parasites lodge in a vital organ or multiply rapidly, they can cause serious problems. Anyone, regardless of personal hygiene, can become infested with parasites. 

 

 Because the human body has only limited natural defenses against parasites, it is almost impossible to eliminate them without treatment. Most types of dangerous infestations are rare in the United States, and the parasite-destroying drugs that are available are highly effective. 

 

 Tapeworm 

 

 Tapeworms are parasites that sometimes infest pigs, cattle, and fish. A tapeworm can be transmitted to a person who eats infested pork, beef, or fish that has not been adequately cooked. Under poor sanitary conditions, tapeworm eggs can be transmitted in the stool of infested people or animals. Once inside the intestines, a tapeworm anchors itself by embedding its head in the intestinal wall. The tapeworm then absorbs food and may grow to more than 30 feet long. A pork tapeworm can cause brain damage (cysticercosis) and liver damage; a fish tapeworm can cause anemia (see page 610). Despite strict government regulations for meatpacking procedures, meat that contains tapeworms occasionally gets on the market. However, thorough cooking will kill any worms in the meat. 

 

 Symptoms 

 

 Segments of the tapeworm break off and are eliminated in stool. In the stool, the worm segments look like short pieces of narrow white ribbon. If the worm remains in the intestines, it often causes symptoms such as weight loss, occasional abdominal pain, loss of appetite, and irritation around the anus. 

 

 Diagnosis and Treatment 

 

 If your doctor thinks you may have a tapeworm, he or she will examine a stool sample and prescribe medication to kill the parasite. The treatment can take several days. You may need to have samples of your stool examined during this time until you pass the tapeworm's head (which indicates an end to the infestation) and follow-up stool tests after 1 month and again 3 months later to make sure the worm has been eliminated. 

 

 Scabies 

 

 Scabies (see page 126) is an infestation with tiny arachnids called mites that burrow under the skin and lay eggs. The mites can be spread through close physical contact such as sexual intercourse or from contact with infested clothes or bedding. Scabies most often affects the hands, wrists, armpits, buttocks, or genital area, rarely the head or face. The mites that cause scabies do not live long once they are removed from the skin. 

 

 Symptoms 

 

 The symptoms of a scabies infestation are caused by an allergic reaction to the insect's excrement and usually develop within 2 to 6 weeks in people who have never been exposed to scabies before, and within 1 to 4 days in people who have previously been exposed. Symptoms include intense itching (usually at night) and red, raised bumps on the skin. Constant scratching can cause sores and scabs to form. 

 

 Diagnosis 

 

 To diagnose scabies, a doctor may apply a blue or black felt-tipped pen to an affected area of the body (usually the area between the fingers). If you have scabies, the ink will seep into the burrows in the skin caused by the mites. The doctor will wash the ink off the surface of the skin to expose the burrows, apply a drop of mineral oil, and scrape the area to get a sample. The sample will be examined under a microscope to check for eggs, mites, and mite feces. 

 

 Treatment 

 

 To treat a scabies infestation, your doctor will prescribe a cream or lotion containing the insecticide permethrin or lindane for you to apply to your entire body below the neck. Follow the directions on the label or your doctor's instructions for application. Wash all infested areas of your body thoroughly before applying the cream or lotion. Do not apply lindane after a hot bath, which can increase the risk that it will be absorbed into the bloodstream, where it can be toxic. Immediately after beginning treatment, wash all contaminated clothing, bedding, and towels in very hot water and dry them in a hot dryer. Ironing everything can also help kill the mites. Spraying your furniture with gamma benzene hexachloride spray can help destroy mites, but be sure to follow the directions on the label carefully and avoid getting the spray in your eyes or on your skin, especially in open wounds or sores. Everyone you've had close contact with should also be treated for scabies. 

 

 Lice 

 

 Lice are tiny, wingless insects that can live on any part of the body and suck blood from the skin. The eggs of lice, known as nits, look like tiny white grains that cling to the hair. Infestations of body lice are rare and can be transmitted through close physical contact and by sharing infested clothing, towels, or bedding. Crab lice, or pubic lice (see page 485), live in pubic hair and are usually spread through sexual contact. Head lice infestations most often occur among schoolchildren. If your child has lice, report it to his or her school. Lice infestations are considered a public health problem, and it is necessary to trace them to their source to prevent them from spreading more. 

 

 Symptoms 

 

 The symptoms of a lice infestation include intense itching at the site of infestation, a feeling of something moving through the hair, and slight redness to severe inflammation of the skin caused by an allergic reaction to the bites. Lice bites pose a slight risk of infection. 

 

 Diagnosis and Treatment 

 

 If you have lice on your scalp or another part of your body, your doctor will recommend treating the affected area with a shampoo or lotion that contains permethrin. Carefully follow the instructions on the package. Then, using a fine-toothed comb or tweezers, remove as many nits as possible. Spray surfaces with a furniture spray that contains permethrin. Wash clothing, bedding, and towels in hot water, and dry them in a hot dryer. If possible, iron them. If any items cannot be cleaned, store them in a plastic bag for at least 2 weeks. 

 

 If lice are present on another part of your body, such as the genitals, inform your sex partner or anyone else with whom you have had close physical contact so he or she can also seek treatment. 

 

 Fleas 

 

 Fleas are tiny, wingless insects that live on and bite animals but that also can bite people. There are many species of fleas, and each one is a parasite of a different animal. Flea eggs hatch in animal bedding about 7 days after they are laid. The fleas live in the bedding and feed off their hosts. Fleas do not stay long on the skin. 

 

 Flea infestations of humans are most common in developing countries and in places with crowded living conditions, close contact between people and domestic animals, or unclean conditions. Fleas can spread lifethreatening diseases such as plague (see page 31). 

 

 Symptoms and Treatment 

 

 Isolated flea bites on the skin can cause a rash and intense inflammation (see page 126) for up to 2 days. If you suspect a flea infestation in your bedding, furniture, or rugs, spray the items with a flea pesticide or repellent. If the infestation is extensive and you are not able to eliminate the fleas, call a professional exterminator. To avoid flea infestations, use antiflea spray, powder, or shampoo on your pet, and spray pet bedding regularly. Flea collars for pets also can be helpful. Apply an insect repellent before going into a flea-infested area. 

 

 Chiggers 

 

 Chiggers (sometimes called red bugs or harvest mites) are a type of mite that lives in grasses, shrubs, and vines. Farmers, hikers, hunters, and others who spend time outdoors are most likely to get chigger bites. The larva (or immature mite) is barely visible (1.100 inch). It attaches to a hair follicle in an area of skin that is thin and moist (usually around the ankles, groin, or waistline), or wherever clothing is tight. The larva releases enzymes that dissolve the skin and then eats the liquefied cells. It feeds for 1 to 4 days in one spot and then drops off. 

 

 Symptoms 

 

 The most common symptom of chigger bites is intense itching in the affected area, especially at night. Some people may have an allergic skin reaction, such as hives (see page 1066) or an itchy, red, pimplelike lump. In some cases, blisters, swelling, or large red patches develop on the skin. 

 

 Treatment 

 

 To treat chigger bites, your doctor may prescribe medication such as antihistamines to relieve itching, corticosteroid creams to reduce irritation and allergic reactions, or antibacterials applied directly to the affected area to prevent bacterial infection. 

 

 Toxoplasmosis 

 

 Toxoplasmosis is a rare infection caused by the parasite Toxoplasma gondii. Found throughout the world, the parasite can infect virtually all warmblooded animals, including livestock, birds, household pets, and humans, but cats are the major host and source of infection. Eating raw or undercooked meat is a less common source of infection. In the United States, about one of five people has been exposed to the parasite that causes toxoplasmosis, but most people have no symptoms because their immune system keeps the infection in check. The parasite remains in an inactive state inside muscle or brain tissue and usually causes no health problems. 

 

 Two groups of people-pregnant women and people who have a weakened immune system- have especially important reasons for avoiding infection with the parasite. A pregnant woman who contracts toxoplasmosis has a 40 percent chance of passing the infection to her fetus, a serious condition called congenital toxoplasmosis, which affects one or two babies of every 1,000 born in the United States each year. In people who have a weakened immune system (such as from an HIV infection or cancer or from taking immune-suppressing drugs), toxoplasmosis can cause life-threatening symptoms affecting the central nervous system and brain. 

 

 Cats, both domestic and wild, are the only hosts that produce the oocyst, the sexually mature and most infectious (to humans) stage of the parasite's life cycle. The parasite multiplies in the cat's intestine, and the oocyst is excreted in the cat's feces. Cats become infected when they eat contaminated rodents or birds, but infected cats have no symptoms. 

 

 Symptoms 

 

 Most healthy people who are infected with toxoplasmosis have no symptoms. Others experience swollen glands, muscle aches, and flulike symptoms that last for a few days to several weeks. Once you have been exposed to toxoplasmosis, you cannot get it again. 

 

 Women who develop toxoplasmosis more than 6 months before becoming pregnant are immune to the infection and cannot pass it on to their fetus. Women who contract toxoplasmosis during pregnancy have a higher-than-normal risk of having a miscarriage or stillbirth and can transmit the infection to the fetus. Infants born with congenital toxoplasmosis often appear normal at birth but develop symptoms such as blindness, deafness, seizures, and mental retardation months or even years later. 

 

 People who have a weakened immune system (such as those who are infected with HIV) cannot fight the infection and will experience headaches, confusion, fever, seizures, poor coordination, and nausea. Dormant toxoplasmosis infections can reactivate in people who have a weakened immune system, causing the same symptoms as those of a new infection. 

 

 Diagnosis 

 

 A blood test can detect the antibodies (infectionfighting proteins) that the body produces after infection by the toxoplasma parasite. If you plan to become pregnant, consider being tested for toxoplasmosis. If the test result is positive (meaning that you have been infected), there is no need to worry about passing the infection to a fetus during pregnancy. If the test result is negative, take precautions to avoid infection (see below). To find out whether a fetus is infected, doctors perform prenatal tests, including amniocentesis (see page 510) and an ultrasound scan (see page 509). 

 

 Treatment 

 

 Most people who are infected with toxoplasmosis need no treatment. Doctors treat infected people who have weakened immune systems with two antiparasitic drugs, pyrimethamine and sulfadiazine; pregnant women who have toxoplasmosis are treated with spiramycin. These drugs also lessen the severity of an infected infant's symptoms both at birth and later in life. 

 

 Prevention 

 

 If you are pregnant or have a weakened immune system because of a chronic illness such as AIDS, take the following precautions to avoid infection with the parasite that causes toxoplasmosis: 

 

 * If you have a cat, don't clean the litter box yourself. Have someone clean it for you every day to reduce the chances of being exposed to infectious toxoplasma oocysts (which take up to 2 days to become infectious). If you have to clean a litter box, put on rubber gloves before you do it and avoid inhaling the dust from the litter box. Dispose of the litter in a tightly wrapped and tied plastic bag. Wash the dust off the gloves with soap and water and rinse them before taking them off. Then wash and rinse your hands thoroughly. 

 

 * Don't eat raw or undercooked meat.especially lamb, pork, or venison.and don't feed it to your cat. Cook meat to an internal temperature of 160??F. Microwaving does not kill the toxoplasma parasite. 

 

 * Wash your hands thoroughly after handling raw meat. 

 

 * Don't taste meat while it is cooking. 

 

 * Keep your cat indoors so it doesn't come into contact with infected birds or rodents. 

 

 * Wear gardening gloves when working in the garden because outdoor cats defecate in soil. Avoid touching your mouth while gardening and always wash your hands after gardening. 

 

 * Stay away from children's sandboxes, or keep them tightly covered. Cats sometimes use them as litter boxes. 

 

 * Wash all fruits and vegetables well before eating them, even if they were grown in your own garden. 

 

 Rabies 

 

 Rabies is a life-threatening disease caused by a virus that is spread to humans through a bite or scratch from an infected animal. Once the rabies virus enters a human, it travels to the nerve nearest the bite and follows the nerve pathway to the brain. In the United States, rabies rarely occurs in dogs or outdoor cats because most are vaccinated annually. The wild animals that most often carry rabies are raccoons, skunks, bats, foxes, and coyotes. 

 

 Symptoms 

 

 The incubation period for rabies (the time it takes from being exposed to the virus until the appearance of symptoms) varies from 10 days to 2 years but is usually about 1 to 3 months. The earliest symptoms of rabies can resemble those of other viral infections and include fever and a general feeling of illness. After 2 or 3 days of feeling ill, a person becomes confused and agitated and has mouth and throat spasms; these symptoms usually last from 2 to 10 days. Trying to drink will worsen the spasms (this is why rabies is also called hydrophobia, which means fear of water). Death usually occurs within 3 weeks after the appearance of symptoms. 

 

 Diagnosis and Treatment 

 

 If you have been bitten or scratched by an animal that could have rabies, call your doctor, 911 or your local emergency medical number, or go to the nearest hospital emergency department immediately. A delay in treatment increases your risk of dying of rabies. If possible, the animal should be captured (but not destroyed) so tests can be performed to determine if it has rabies. You will probably be given an injection of immune globulin (proteins that fight the rabies virus) and a five-shot series of rabies vaccine to help prevent the disease from developing. The injections are usually given in the arm over a period of 28 days. 

 

 Lyme Disease 

 

 Lyme disease is an infection caused by bacteria that are transmitted to humans through the bites of infected ticks that live on animals such as deer, mice, rabbits, and raccoons. The ticks that carry Lyme disease can also carry ehrlichiosis (see page 945) and babesiosis (see page 944). Lyme disease can occur in anyone who is bitten by an infected tick. 

 

 Symptoms 

 

 A person who has been bitten by an infected tick usually develops a red spot on the skin that gradually increases in size (see page 126). The center of the spot returns to its normal color after a day or two, leaving a bull's-eye appearance on the skin that may be painless. In some cases, the skin clears up and the person has no other symptoms. However, in other cases, more red spots appear within a day or two and the person may have a headache, fever, swollen lymph glands, and pain in the joints and muscles. He or she may also feel generally ill and weak. 

 

 If Lyme disease is not treated, it progresses to a second stage of illness, in which the disease affects the nervous system and heart. Partial paralysis of the muscles served by the facial nerves and other affected nerves may occur. The person may also develop meningitis (see page 692), which is inflammation of the meninges (the coverings of the brain and spinal cord). Meningitis causes severe headache, sensitivity to light (photophobia), and generalized weakness. Rarely, an irregular heartbeat and inflammation of the heart and pericardium (the heart's covering) can occur. 

 

 If the second stage is not treated, a third stage will occur in which a person may develop chronic arthritis that affects the larger joints such as the knees. 

 

 Diagnosis and Treatment 

 

 A diagnosis of Lyme disease can be confirmed by blood tests. 

 

 Lyme disease is treated with doxycycline or another antibiotic (children are treated with amoxicillin). If Lyme disease is diagnosed and treated in its early stages, the outlook is good. Once chronic arthritis has developed, however, treatment is less successful. Additional treatment may be necessary if symptoms recur. 

 

 Rocky Mountain Spotted Fever 

 

 Rocky Mountain spotted fever is a potentially lifethreatening infection caused by rickettsia bacteria that are transmitted through tick bites. Although ticks that carry the rickettsia bacteria are found all over the United States, the disease most frequently occurs in the Southeast, from Maryland to Georgia. Rocky Mountain spotted fever usually occurs in the spring and summer in people who spend a lot of time outdoors. 

 

 A person who has been infected with the bacteria may not notice the tick bite that caused the disease. If you find a tick embedded in your skin, remove it as soon as possible (see above). The risk of becoming infected increases if the tick stays attached to your body for several hours or if you crush the tick while trying to remove it. Untreated, Rocky Mountain spotted fever can be fatal. 

 

 Symptoms 

 

 Symptoms of Rocky Mountain spotted fever develop from about 2 days to several weeks after exposure to the bacterium. Symptoms include severe headache, fever (up to 105°F), and severe muscle aches and weakness. Other symptoms can include chills, abdominal pain, nausea, spasms in the back, and mental confusion. Most people develop a characteristic rash (2 to 5 days after a bite) that usually begins as flat red spots on the palms of the hands and on the soles of the feet. The rash spreads to the wrists, ankles, legs, arms, and finally the trunk. Later stages of the disease include damage to the kidneys, liver, and lungs. Eventually, the person loses consciousness. 

 

 Diagnosis 

 

 Doctors diagnose Rocky Mountain spotted fever by taking two consecutive blood tests to check for antibodies (specific proteins the body produces to fight the bacteria). The second test is done 10 to 14 days after the illness begins to see if the level of antibodies has increased, which indicates an active infection. 

 

 Treatment 

 

 To treat Rocky Mountain spotted fever, your doctor will prescribe antibiotics as soon as the infection is diagnosed (because there is an increased risk of organ damage and death if treatment is delayed). If the disease is not treated right away, you may have to be hospitalized to treat any organ damage. 

 

 West Nile Virus Infection 

 

 West Nile virus is spread by the bites of infected mosquitoes and can infect people, birds, horses, and some other animals. The virus does not appear to spread from person to person or from animal to person but it may be transmitted through infected donor organs or in blood transfusions. In northern climates, most cases develop in late summer or early fall. In southern climates, the virus can be transmitted throughout the year. Most people who are infected have mild symptoms or no symptoms at all. However, in rare cases, the infection can cause severe symptoms and can be fatal. People over age 50 are more likely to have a severe infection. An estimated 1 in 150 people infected with the virus develops a severe form of the disease. 

 

 Symptoms 

 

 Symptoms of a West Nile virus infection usually develop from 3 to 14 days after the infecting mosquito bite. A mild case, called West Nile fever, is characterized by flulike symptoms such as fever, headache, body aches, and, sometimes, a rash on the trunk and swollen lymph nodes. The symptoms in mild cases usually last only a few days and don't cause any long-term health effects. Infection with West Nile virus may provide lifelong immunity to the virus. 

 

 The symptoms of more severe infections-West Nile encephalitis (inflammation of the brain), meningitis (inflammation of the membranes surrounding the brain and spinal cord), and meningoencephalitis (inflammation of the brain and the membrane surrounding it)-include headache, a high fever, a stiff neck, disorientation, muscle weakness, tremors, seizures, coma, and paralysis. These symptoms can last several weeks and their effects on the brain can be permanent or fatal. 

 

 Diagnosis 

 

 To diagnose a West Nile virus infection, a doctor will take a detailed health history to evaluate a person's risk of infection, such as being in an area where the virus has been detected. If your doctor thinks you may be infected or if you have symptoms, he or she will take a sample of blood and send it to a laboratory for microscopic examination to detect the virus. 

 

 Treatment 

 

 There is no specific treatment for a West Nile virus infection. Mild cases generally clear up on their own. For severe infections, people are usually hospitalized and given intravenous fluids and antibiotics (to prevent or treat secondary bacterial infections such as pneumonia). If breathing is affected, a person may need to use a ventilator to temporarily assist breathing. 

 

 Babesiosis 

 

 Babesiosis is a rare, potentially life-threatening disease caused by the Babesia microti parasite, which is spread to people through the bites of infected ticks that live on animals such as deer and mice. Babesiosis also can be transmitted through blood transfusions. The parasite that causes babesiosis attacks red blood cells. 

 

 Babesiosis can be mild or severe. Most people who are infected do not become sick. However, older people and people who have an impaired immune system or who have had their spleen removed (splenectomy) are at increased risk of developing a severe infection. If not treated, babesiosis can cause extremely low blood pressure, hemolytic anemia (see page 616), liver problems, and kidney failure in high-risk people. 

 

 Although babesiosis usually occurs in the coastal areas of the northeastern United States, cases have been reported on the West Coast and in the Midwest. The tick that carries Lyme disease (see page 942) and ehrlichiosis (see below) can also carry babesiosis, and a person can be infected with a combination of the diseases at the same time. If you find a tick embedded in your skin, remove it as soon as possible (see page 943). 

 

 Symptoms 

 

 Symptoms of infection with babesiosis may develop from 1 week to a month after a bite by an infected tick. Symptoms can include fatigue and a general sense of feeling ill. Later symptoms may include headache, fever, muscle and joint aches, and drenching sweats. 

 

 Diagnosis and Treatment 

 

 To diagnose babesiosis, your doctor will take a detailed health history and perform blood tests to check for antibodies (proteins the body produces to fight the parasite) or for the parasite itself. The disease can be difficult to diagnose in older people and in people who have other health problems. 

 

 Although most people do not need treatment for an infection with babesiosis, a doctor may prescribe a combination of antiparasitic medications for those at risk of severe illness or complications. 

 

 Ehrlichiosis 

 

 Ehrlichiosis is an infection caused by ehrlichia bacteria, which can be transmitted to people in tick bites. The infection has two forms-monocytic and granulocytic. Human monocytic ehrlichiosis is caused by a type of ehrlichia bacterium that attacks the infection-fighting white blood cells called monocytes. The bacterium that causes the granulocytic type, which also affects humans, attacks white blood cells called granulocytes. Human monocytic ehrlichiosis occurs mainly in the south central and southeastern parts of the United States. Human granulocytic ehrlichiosis occurs in the Northeast, the Midwest, and in northern California. 

 

 Some people who are bitten by a bacteriacarrying tick may not develop ehrlichiosis. However, older people, people who have an impaired immune system, and people who have had their spleen removed (splenectomy) are at increased risk of developing a severe infection. If you find a tick embedded in your skin, remove it as quickly as possible (see page 943). 

 

 Symptoms 

 

 The initial symptoms of ehrlichiosis may develop 5 to 10 days after a bite from an infected tick and include fatigue and a general feeling of illness. Other symptoms include fever, headache, and muscle and joint aches. People who develop a severe infection may also have nausea, vomiting, diarrhea, and a rash. 

 

 Diagnosis and Treatment 

 

 To diagnose ehrlichiosis, your doctor will take a detailed health history. He or she also may perform blood tests to check for antibodies (proteins the body produces to fight the bacterium) or for the bacterium itself. The doctor also may test your blood for a decrease in platelets (sticky cell fragments that enable blood to clot) and infectionfighting white blood cells. The blood test is performed when the symptoms begin and again 4 to 6 weeks later. A doctor will prescribe antibiotics to treat ehrlichiosis. Be sure to follow your doctor's instructions when taking the antibiotic to make sure you eliminate the infection. 

 

 Travelers' Infections 

 

 If you are planning a trip out of the country, make sure that you are adequately protected against any diseases that can occur in your country of destination. Many developing countries do not have adequate water or sewage systems. For this reason, diseases linked to contaminated water supplies- such as dysentery (see page 948), typhoid (see page 948), and polio (see page 695)-are common in many developing countries. 

 

 About 6 weeks before you leave on your trip, find out from your doctor which vaccinations are necessary for entry into the country and which are recommended. The US Centers for Disease Control and Prevention (CDC) is also a good source of information (www.cdc.gov). At least 1 month before you travel, see your doctor or go to a clinic that specializes in travelers' health and get any immunizations you may need; many vaccinations are not immediately available or must be taken well in advance of a trip. For example, if you plan to visit (even if only for a few hours) any of the countries in which malaria (see next page) is endemic (always present), you should begin antimalarial drug treatment before your trip and continue it after you leave the malaria-infested country. The length of the treatment time depends on the drug used. You can be immunized against typhoid and polio. 

 

 Depending on your destination, you may be advised to have one or more of the following vaccinations: 

 

 * Hepatitis A and B 

 

 * Yellow fever 

 

 * Meningococcal meningitis 

 

 * Rabies 

 

 * Polio booster 

 

 * Tetanus booster 

 

 * Measles booster 

 

 Tropical countries have insects, including mosquitoes and flies, that transmit diseases such as yellow fever (see page 949). If you swim or bathe in developing countries, or walk barefoot there, you risk becoming infested with parasitic worms such as schistosomes or hookworms. Schistosomes, or blood flukes, can be found in fresh water and can enter your body through the skin. In some cases, these parasites cause only a skin condition called dermatitis (see page 1062). In other cases, infestation with schistosomes results in a disease called schistosomiasis, or bilharziasis. In this disease, the parasites travel from the skin to the bladder and the intestines, from where they may spread to other parts of the body. The severity of the disease depends on the number of parasites that enter your body. 

 

 Hookworms are parasitic roundworms that are found in developing countries, particularly in areas with poor sanitation. Larvae of the parasite live in the soil, and your risk of infestation increases if your skin comes in contact with infested soil or if you eat or drink contaminated food or water. The hookworms enter the bloodstream and travel to the lungs. From the lungs they travel to the trachea, are swallowed, and end up in the small intestine. The worms then "hook" themselves to the lining of the intestine, where they feed on blood, causing blood loss. Severe infestations can result in anemia (see page 610). 

 

 While you are traveling in a developing country, the following precautions can help you stay healthy during your trip: 

 

 * Wash your hands before handling or eating food. 

 

 * Drink only bottled water or milk, or boil water to make it safe to drink. Alternatively, use both a water filter and iodine tablets to purify water and other liquids by the glassful. Avoid ice cubes. Carbonated beverages such as colas in sealed cans and bottles are usually safe. 

 

 * Do not use tap water for brushing your teeth. 

 

 * Avoid salads and reheated foods. Do not eat peeled fruit; always peel it yourself. 

 

 * If you plan to visit rural or remote areas, make sure that your clothing protects you adequately from insect bites, especially if you plan to sleep outside or travel at night (when insects can be most active). Wear long-sleeved shirts, long pants, and socks when traveling. 

 

 * Use an insect repellent containing DEET or permethrin (in a 35 percent solution for adults and a 6 to 10 percent solution for children). 

 

 * Stay in air-conditioned or well-screened areas. 

 

 * Don't use scented products such as lotions or perfumes, which can attract some insects. 

 

 Cholera 

 

 Cholera is a disease caused by bacteria that damage the intestinal lining. The bacteria are transmitted through polluted water, shellfish, or raw fruits and vegetables in places where sanitation is poor. Cholera seldom occurs in developed nations. When it does, it usually can be traced to visits to (or residence in) developing countries. However, every year the US Public Health Service reports a few cases of illness caused by contamination of American shellfish with bacteria related to the cholera bacillus. 

 

 Symptoms 

 

 The symptoms of cholera are abdominal pain and severe diarrhea. Cholera can cause such severe diarrhea that up to 4 gallons of fluid are lost in a day. A person who has cholera may have bowel movements resembling murky water that may be passed almost continuously. He or she may have muscle cramps, extreme thirst, and sudden vomiting, sometimes without the usual initial feeling of nausea. If dehydration is not treated immediately, cholera can be fatal quickly. If you are abroad or have just returned home and have extremely watery, continuous diarrhea that does not improve within a couple of hours, get medical help immediately. 

 

 Diagnosis and Treatment 

 

 If you have symptoms of cholera, see your doctor immediately. He or she will ask for stool samples to look for the bacteria in the stool. He or she may also order a blood test to look for antibodies (infectionfighting proteins) produced by the immune system to fight the cholera-causing bacteria. 

 

 The main treatment for cholera is to prevent or treat dehydration by replacing fluids. If the diarrhea is severe, you may need to be hospitalized. You will be given a rehydration fluid either orally or intravenously (through a vein) until your body chemistry is restored to normal. Your doctor also may prescribe an antibiotic. 

 

 Malaria 

 

 Malaria is a disease caused by any of four species of parasites called plasmodia that are transmitted from one person to another through the bite of an Anopheles mosquito (the only carrier). Plasmodia enter the bloodstream only if the Anopheles mosquito that bites you has previously bitten a person who has malaria. 

 

 Once in the bloodstream, the plasmodia travel to the liver, where they multiply rapidly. After 9 to 16 days, thousands of plasmodia flow back into the bloodstream, where they destroy oxygen-carrying red blood cells, which can result in anemia (see page 610) and a high fever. Many plasmodia remain in the liver cells and continue the cycle of multiplying, entering the bloodstream, and destroying red blood cells. When the parasites inside the red blood cells mature, they rupture the cells and reenter the bloodstream. The destroyed red blood cells can form small clumps, which can block blood vessels, potentially leading to brain or kidney damage. One species of the plasmodia causes an especially dangerous infection called falciparum malaria, which can cause massive, potentially fatal blood vessel blockages. 

 

 In most forms of malaria, a person usually has repeated attacks unless the disease is treated. Each attack signals the release of plasmodia into the bloodstream. If malaria is not treated, attacks can occur for years. However, as the immune system slowly builds up a defense against the disease, the attacks occur less and less frequently. 

 

 The Anopheles mosquito is found in the southeastern and western United States and in tropical and semitropical countries. Mosquito abatement programs have virtually eradicated malaria in the United States. With the exception of a few cases each year, nearly all cases of malaria in the United States are brought back by people who have traveled to other countries. 

 

 Symptoms 

 

 The symptoms of malaria depend on the type of plasmodium carried by the mosquito and usually appear about 8 to 30 days after a mosquito bite. A full day of headache, fatigue, and nausea is followed by 12 to 24 hours of chills alternating with fever. A sudden chill is followed by a stage of fever with no sweating, and rapid breathing. A drop in temperature accompanies a final sweating stage. Similar bouts occur whenever more plasmodia are released into the bloodstream, generally every 2 or 3 days. 

 

 Children with malaria are likely to have prolonged high fever without chills. The fever sometimes affects the brain, causing unconsciousness or seizures (see page 686). 

 

 In falciparum malaria, the most severe form, all the plasmodia are released from the liver into the bloodstream at the same time, resulting in a single extremely severe attack. The alternating chills and fever can last 2 or 3 days. If the person recovers, however, the attacks do not recur. 

 

 Diagnosis and Treatment 

 

 If you develop symptoms of malaria, see your doctor immediately. He or she will order blood tests. Because it is not always easy to detect the presence of plasmodia in the blood, you may need to have blood tests periodically. If blood tests show that you have malaria, the doctor will prescribe an antimalarial medication. 

 

 Prevention 

 

 To protect against malaria, when you are planning to visit an area in which the disease is prevalent, your doctor will prescribe antimalarial drugs. You need to start taking the drugs before your trip and continue to take them after you return. In many parts of the world, malaria parasites have become resistant to some of the more common drugs used against them such as chloroquine, but newer and more effective drugs are constantly being developed. 

 

 Amebic Dysentery 

 

 Amebic dysentery, also known as amebiasis, is an intestinal illness caused by infection with a microscopic parasite (ameba). Amebic dysentery is prevalent in developing countries that have poor sanitation. Contaminated water and lack of proper hygiene among food handlers can spread the organisms that cause amebic dysentery. In the United States, amebic dysentery is transmitted most frequently through oral-anal sex. 

 

 Symptoms 

 

 The main symptom of amebic dysentery is diarrhea, which can contain blood and may persist for weeks if not treated (resulting in weight loss). Other symptoms include abdominal cramps, excessive gas, and fatigue. After the diarrhea subsides, it may recur from time to time. In rare cases the organisms spread from the digestive tract into the bloodstream and settle in the liver, where they form abscesses (pus-filled sacs). 

 

 Diagnosis and Treatment 

 

 If you have symptoms of amebic dysentery, your doctor will ask for stool samples to look for the parasite in the stool. He or she also may order a blood test to look for antibodies (proteins the body produces to fight the parasite) or for the parasite itself. The doctor may also recommend a sigmoidoscopy (see page 144) to view the lower part of the colon directly. If you have amebic dysentery, the doctor will prescribe antiparasitic drugs to be taken for about 10 to 20 days. Make sure you wash your hands thoroughly after you use the toilet to avoid reinfecting yourself or spreading the infection to others. After the diarrhea has stopped, your doctor will want to examine samples of your stool monthly until no infecting organisms are found. 

 

 Typhoid Fever 

 

 Typhoid fever is an infectious disease spread under unsanitary conditions from person to person or through contaminated food or water. Some people carry typhoid-causing bacteria in their body after they have the disease (even without having symptoms) and can infect others. Typhoid fever is rare in the United States, although the disease occurs occasionally in rural areas. Nearly all cases can be traced to recent travel or residence in a developing country. If you are planning to travel to a developing country, talk to your doctor. Depending on the country, he or she will probably recommend that you have a vaccination against typhoid. 

 

 Symptoms 

 

 The symptoms of typhoid fever begin suddenly with headache, loss of appetite, and vomiting followed by a persistent fever of about 104°F, chills, increasing weakness, diarrhea (usually bloody), and, often, delirium. Early in the disease, you may have a pink rash on your abdomen (called rose spots), which then fades. In severe cases, a person can have extensive gastrointestinal bleeding or rupture of the intestines, which can be life-threatening. 

 

 Diagnosis and Treatment 

 

 If you have recently returned from a developing country and have symptoms of typhoid fever, see a doctor immediately. If he or she suspects you could have typhoid fever, you will be admitted to a hospital isolation unit. You may have a blood test to look for antityphoid antibodies (proteins the body produces to fight the bacteria) or to detect the bacterium itself. A doctor may also take a stool sample to look for the bacteria. If you have typhoid fever, your doctor will prescribe antibiotics, which you will need to take for about 7 to 14 days. It may be several more weeks before your digestive tract is free of infectious bacteria; during this time, you can still transmit the infection to others. To make sure that you are free of typhoid bacteria, your doctor will examine a sample of your stool each month for at least 3 months (longer if you are a food handler). 

 

 Yellow Fever 

 

 Yellow fever is a disease caused by a virus that damages the liver and kidneys. The virus is transmitted through Aedes mosquito bites and occurs in South America and Africa. As with many viral infections, there is no effective treatment for yellow fever. A person who has recovered from yellow fever is immune to it for life. A vaccine is available to prevent yellow fever in people who are traveling to countries where the disease may be prevalent. However, the vaccination is not recommended for children younger than 6 months, pregnant women, or people who are allergic to eggs or who have a weakened immune system. 

 

 Symptoms 

 

 The symptoms of yellow fever, which develop 3 to 6 days after the infecting mosquito bite, can be mild to severe. A mild case produces symptoms that resemble those of the flu (see page 649). Symptoms of more severe cases include fever, headache, abdominal pain and vomiting, bleeding from the gums, frequent nosebleeds, easy bruising, blood in stool or vomit, and yellowing of the skin and whites of the eyes (jaundice; see page 785). Other possible symptoms include confusion, kidney failure, and coma. 

 

 Diagnosis and Treatment 

 

 To diagnose yellow fever, a doctor will perform blood tests to check for antibodies (proteins the body produces to fight the virus) or for the virus itself. 

 

 There is no treatment for yellow fever. You will be given a rehydration fluid either orally or intravenously (through a vein) to replace lost fluids. If you develop a bacterial infection, your doctor will prescribe an antibiotic. 

 

 Dengue 

 

 Dengue is an infection caused by a virus that is transmitted through the bites of Aedes mosquitoes. Dengue infections occur in Central and South America, the Caribbean, the South and Central Pacific islands, Southeast Asia, China, India, the Middle East, and Africa. 

 

 Symptoms 

 

 The symptoms of dengue, which develop 8 to 10 days after the infecting mosquito bite, occur suddenly and resemble those of other viral infections, such as high fever, headache, nausea and vomiting, and joint and muscle pain. The joint and muscle pain is so severe that dengue is often called breakbone fever. A rash may appear 3 to 4 days after a fever develops. Dengue can last up to 10 days, but complete recovery can take 2 weeks to a month. In severe cases, dengue progresses to a lifethreatening complication called dengue hemorrhage, which is characterized by severe bleeding that can be fatal. 

 

 Diagnosis and Treatment 

 

 To diagnose dengue, a doctor takes a detailed health history and orders blood tests to check for antibodies (infection-fighting proteins the body produces to fight the virus) or for the virus itself. If you have recently traveled to any area where dengue is prevalent and have symptoms, tell your doctor. 

 

 To treat dengue, doctors usually recommend bed rest, plenty of fluids, and a pain reliever such as acetaminophen. People with dengue should not take aspirin because aspirin interferes with blood clotting and can increase the risk of bleeding. 

 

 Leishmaniasis 

 

 Leishmaniaisis is a potentially life-threatening disease caused by a parasite that is transmitted through the bites of infected sand flies. In very rare cases, leishmaniasis can be transmitted through blood transfusions, and from a pregnant woman to the fetus. The most common types of leishmaniasis are cutaneous leishmaniasis, mucosal leishmaniasis, and visceral leishmaniasis. The majority of cases occur in countries in South America, South Asia, and Africa. Leishmaniasis is also found in some parts of Central America, Mexico, and the Middle East. Although very rare in the United States, cutaneous leishmaniasis infections have occurred in rural areas of southern Texas. 

 

 Symptoms 

 

 The symptoms of cutaneous leishmaniasis-skin sores that