health

Keeping Pathogens Out MAIN IDEA Your body has five major barriers that defend against pathogens. Pathogens are everywhere. They are on almost all of the surfaces you touch. They are in the air you breathe. So, why aren't you sick all of the time? Your body has natural barriers between you and pathogens. They work to keep pathogens out of your body. These barriers are your body's first line of defense. The five major barriers are skin, tears, saliva, mucous (MYOO-kuhs) membranes, and stomach acid. Your skin is your body's largest organ. It is a barrier or wall around the inner organs. The skin produces salty sweat. Most pathogens don't like salt. The skin also has one-way pores. Sweat can get out, but pathogens can't get in. Body fluids such as tears and saliva form another barrier. Tears and saliva contain chemicals that kill certain organisms. Mucous membranes are another barrier. They line the insides of your mouth, throat, nose, and eyes. They are coated with a sticky fluid that traps and destroys pathogens. Stomach acid, another barrier, kills the germs that make it past the saliva and mucous membranes in your mouth. Even with all of these barriers, pathogens sometimes find their way into your body. They might get in through a cut or scrape. If pathogens enter the body, you might have an infection. Your body is well-equipped to handle the infection. Infection can trigger a fever in the body. The increase in body temperature caused by the fever makes it difficult for pathogens to live.

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Nonspecific Immune Response MAIN IDEA Your immune system responds when pathogens get past the five major barriers of protection. Sometimes your body's barriers can't keep out all of the pathogens. For example, when you get a splinter, it breaks the skin. The pathogens that are on the splinter enter your system through the broken skin. When this happens, your immune system responds to the invaders. The response is called a nonspecific immune response. It's called nonspecific because your body reacts the same no matter what foreign matter enters the body. The splinter or other foreign object will cause the skin around it to become red and sore and swollen. The nonspecific immune system has responded with inflammation. When the splinter enters your system, the brain tells white blood cells to rush to the area. White blood cells destroy the pathogens. When this happens, circulation to the area slows down. When your body has inflammation or other infection, it produces a protein called interferon (in•ter•FIR•ahn). Interferon stimulates the body's immune system. This helps to stop pathogens from multiplying. If pathogens do multiply and spread, your body temperature may rise. This will cause a fever. A higher body temperature makes it difficult for pathogens to reproduce and multiply. The fever also signals the body to produce more white blood cells. The white blood cells attack and destroy the pathogens.

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It's possible that some pathogens will get past the body's nonspecific immune response. When this happens, the body responds with a specific immune response. This is the immune system's second response. Each specific response is customized to attack a particular pathogen and its poisons, or toxins. Your immune system recognizes pathogens that have invaded before. Your body battled those pathogens. The particular response cells that did battle stay in your body. So if the same types of pathogens attack again, those response cells go into action. They attack and fight the pathogens very quickly. The second response is faster than the first response. The figure in the Lesson Resources panel provides a complete explanation of the immune system response. The Lymphatic System The lymphatic system is an important part of the body's defense system. It contains fluid called lymph. The lymph flows into the body's tissues and blood stream fighting pathogens. The lymphatic system contains lymphocytes (LIM•fuh•sytes). There are three main types of lymphocytes: B cells, T cells, and NK cells. NK stands for "natural killer." Natural killer cells attack cancers and viruses. B cells are made in the bone marrow. T cells are made in the thymus. B cells and T cells work together to defeat invading pathogens. T cells are like a military intelligence unit. They identify the invaders. Then they send out a chemical communication or alert to the B cells. The B cells attack and kill the invading pathogen. Macrophages are also found in the lymph. Macrophages surround and destroy foreign substances in the body. Then they remove the foreign material from the lymph. They also remove waste products and harmful organisms. Antigens and Antibodies Antigens and antibodies are both invaders. One tries to introduce infection to the body. The other fights that invasion. Antigens are invaders that force the body to react. Antibodies are proteins that attach to antigens to fight the invaders. The three types of lymphocytes—T cells, B cells, and NK cells—react to antigens. The lymphocytes are activated when the body recognizes a part of a pathogen called an antigen. For example, if bacteria enter your system, lymphocytes will recognize substances on the surface of the bacteria as antigens. Also, blood that is a different type than your will be recognized as an antigen. Your body reacts to antigens by making more B cells and T cells. B cells make antibodies. Antibodies fight a particular type of antigen. Using the example from above, special antibodies will attack the antigens on the bacteria. Different antibodies will attack the antigens on the blood. Some of the new B cells and T cells don't react to the antigens the first time. They wait to react if the same kind of pathogen enters the body again. These are known as memory B cells and memory T cells. T cells either stimulate the production of B cells or attack pathogens directly. There are two main types of T cells: helper cells and killer cells. Helper cells activate the production of B cells. Killer cells attach to invading pathogens and destroy them.

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You have several different types of immunity. You are born with natural immunities. For example, there are germs that affect animals that do not affect you. When your pet gets sick, you probably won't get sick from your pet. Pathogens such as distemper that might make your pet sick won't make you sick. The reverse is also true. Pathogens that make you sick probably won't make your pet sick. Other barriers also provide immunity. Those barriers include tears, mucous membranes, saliva, skin, and stomach acid. These barriers can be penetrated by pathogens. If that happens, your immune system takes over to attack the invading pathogens. Babies are born with natural immunities. The mother's antibodies pass from her body to the body of her baby. After the baby is born, the mother's milk provides additional antibodies. These antibodies help the baby's immune system fight pathogens. After the first few months of life, a baby's own immune system begins to fight pathogens. Your body builds immunity when it responds to pathogens. It also builds immunity when you get certain diseases. When your body encounters antigens, it makes memory B cells and T cells. These memory cells remember the antigens the next time they invade your body. Then they produce antibodies to fight the antigens. Scientists discovered many years ago that they can help the body develop immunities. They can do this by introducing a vaccine into the body. Vaccines help the immune system make antibodies for certain diseases. Diseases vaccines have been developed for include: polio, measles, and chicken pox. Vaccinations such as those for hepatitis B must be given several times over a few months. The vaccine for tetanus must be given throughout your life. It is important to keep vaccinations up to date. The chart in the Lesson Resources panel shows when common vaccinations should be given. Keeping vaccinations up to date helps keeps you healthy. It also helps keep those around you healthy.

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Have you ever had a cold? You probably have. Most people have at least one cold each year. The cold is the most common communicable disease. Colds are responsible for more school absences than any other illness. Cold symptoms include runny nose, headache, sore throat, coughing, sneezing, and mild fever. You might be wondering, if colds are so common, why they can't come up with a vaccine to guard against colds. Well, there are hundreds of different viruses that are responsible for the common cold. Because there are so many, scientists can't develop vaccines for all of them. Besides, scientists believe there are probably twice as many viruses that cause the cold than they already know about. The common cold is here to stay. So, what can you do if you have a cold? The first thing you should do is protect others. When you sneeze, cover your nose and mouth to prevent the infection from spreading. When you sneeze, thousands of infected droplets containing the cold virus are released into the air. They can be spread through direct or indirect contact to others. To recover from a cold, rest in bed. During the first 24 hours your cold is contagious. So, it is best if you stay at home and don't infect others. Your parents might also give you over-the-counter medicines to help relieve your cold symptoms. You should also drink plenty of fluids when you have a cold. If your cold symptoms get worse, or your sore throat lasts for several days, you should see a doctor.

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Your joints and muscles ache. You have fever, chills, fatigue, and a headache. You have the flu. Influenza (in•floo•EN•zuh), or the flu, is another communicable disease. You'll notice the symptoms of the flu are different from the common cold. Flu symptoms usually affect you more quickly and more seriously than cold symptoms do. Like a cold, though, flu can be spread through both direct and indirect contact. Resting and drinking lots of fluids can help you recover faster from the flu. Some types of flu are serious and require a doctor's care. December through March is considered to be "the flu season." This is because most cases of the flu are reported during these months. Flu viruses are not the same as the viruses that cause colds. Every year, certain strains of the flu virus are stronger and spread faster than the year before. Scientists meet every year to determine which strains will spread fastest during the next flu season. Then they develop vaccines for those strains of flu. Some types of flu can be dangerous. Just after World War I, a flu outbreak killed about 20 million people around the world. Over 600,000 of those people were in the United States. Today scientists are doing their best to keep that kind of flu outbreak from happening again.

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Communicable diseases have a contagious period. Often, the contagious period begins before the person starts to show symptoms. The contagious periods for several communicable diseases are listed in the Lesson Resources panel. Chicken pox, measles, and mumps all have specific contagious periods. Chicken pox is contagious for about a week before symptoms appear. Typical symptoms for chicken pox include an itchy, bumpy rash, fever, and aching muscles. The itchy bumps will blister and then dry up. When they are dry, chicken pox are no longer contagious. A vaccine for chicken pox became available in 1995. Since then, the disease is much less common. Measles has symptoms that include a rash, fever, and head and body aches. Measles are contagious a few days before symptoms appear. The contagious period lasts about five days after the symptoms appear. Measles is a dangerous disease. Around the world, over 1 million children die each year from measles. Vaccines are available in the United States and some other countries. Because of the vaccine, measles is less common than it once was. Mumps causes a fever, headache, and swollen salivary glands. Mumps are contagious about a week before symptoms appear and for about nine days after that. More than 90 percent of the children in the United States are vaccinated against mumps. Fewer people get the disease now.

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Hepatitis Hepatitis (hep•uh•TY•tis) has several symptoms. Yellowing of the skin and whites of the eyes and inflammation of the liver are common symptoms. Other symptoms include fatigue, weakness, loss of appetite, fever, headaches, and sore throat. There are three common strains of hepatitis: A, B, and C. A different virus causes each strain. Hepatitis A is commonly found in areas that have poor sanitation. It spreads when infected human wastes contaminate the food and water sources. If someone consumes contaminated water or food, they can become infected. An open wound that is cleaned with contaminated water can also cause the infection to spread. There is no treatment for hepatitis A. However, it will usually clear up in a few months. Rest and healthful food choices help in the recovery from hepatitis A. Hepatitis B and C can be more dangerous. These strains can cause permanent damage to the liver. They can lead to cirrhosis and liver cancer. These types of hepatitis are usually spread through contact with infected blood or other body fluids. They can spread when drug users share needles. They can also spread through sexual contact. There are vaccinations for hepatitis A and B. There are medications that can help treat hepatitis B and C. Tuberculosis Symptoms of tuberculosis (TB) (too•ber•kyuh•LOH•sis) include cough, fatigue, night sweats, fever, and weight loss. It is spread through the air when an infected person coughs or sneezes. The cough or sneeze carries tiny droplets that are then inhaled by another person. A person can have tuberculosis, or TB, and not even know it. He or she may not show any symptoms. They may not be sick, but they can still spread the disease. Doctors and other health care providers often test people to be sure they do not carry TB. Tuberculosis can be treated with medications. However, the treatment period is longer than for most other bacterial infections. Treatment for TB can take up to nine months. Your age, overall health, and type of medication used determine how long it might take. If TB is not treated properly, it can be fatal. Until 1985, TB was rare in developed countries. The spread of HIV, the virus that causes AIDS, has contributed to the increase in TB. People with HIV have a weakened immune system. This keeps them from fighting off bacterial infections such as TB. In countries where TB is a problem, babies are given a vaccination for TB. The vaccination is not 100 percent effective. So, scientists are working to develop a better vaccine. Pneumonia Pneumonia is usually caused by bacteria or viruses. Bacteria or viruses live in your sinuses, nose, mouth, and the environment. When these spread to your lungs, pneumonia can occur. Symptoms include fever, cough, chills, and nausea. Pneumonia can also cause vomiting, chest pains, and difficulty breathing. Pneumonia is spread through direct or indirect contact with an infected person. You can catch it from people whether or not they show symptoms of illness. Pneumonia caused by bacteria can be treated with antibiotics. Pneumonia caused by viruses can be treated with antivirals. People with pneumonia need to rest and drink plenty of fluids. People who have other illnesses such as diabetes or HIV/AIDS are at greater risk to catch pneumonia. There are ways to lower your risk for getting pneumonia. First, pneumonia can be prevented with vaccines. Next, practicing good hygiene can reduce your risk for pneumonia. Wash your hands often and thoroughly. Keep hard surfaces such as counters and desks that you touch often clean. Cough or sneeze into a tissue or into your elbow or sleeve. Reduce your exposure to cigarette smoke. All of these can help reduce your risk for pneumonia. Strep Throat Have you ever had a sore throat? Sore throats can be very painful and uncomfortable. Most sore throats are caused by a virus. Strep throat is caused by bacteria. So it can be treated with antibiotics. Strep throat is spread through direct or indirect contact. When someone infected with strep throat breathes or coughs, they release droplets into the air. If you happen to breathe in some of those droplets, you will likely get strep throat. How do you know if you have strep throat? If you have a red and painful throat, fever, and swollen lymph nodes in your neck, you may have strep throat. Your symptoms might also include headache, nausea, and vomiting. If you have these symptoms, get medical help. If strep throat is left untreated, it can lead to more serious illnesses. It can lead to rheumatic fever, which can damage the heart. It can also lead to nephritis, which can damage the liver. Treatment with antibiotics can prevent these illnesses.

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Sexually transmitted diseases (STDs) are also called sexually transmitted infections (STIs). The pathogens that cause STDs are transferred from person to person through sexual contact. A person who has sexual relations with someone who has an STD can be infected with the disease. Many times, a person with an STD may not even be aware that they have a disease. Some STDs are silent, meaning that they have mild or no symptoms. The figure in the Lesson Resources panel gives you some important facts about STDs. STDs are a major health problem in the United States. The Centers for Disease Control and Prevention (CDC) tracks health issues in the United States. In 2017, the CDC reported that 2.3 million new cases of three STDs were diagnosed in the U.S. This is a 31 percent increase over previous years. Treating STDs costs the U.S. about $16 billion each year. If untreated, many STDs can cause infertility. The CDC estimates that young people make up about 27 percent of the sexually active population in the United States. This age group experiences about 50 percent of all STDs. The message is that if you're young, practice abstinence to avoid STDs.

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STDs are passed from one partner to another through sexual activity. All STDs affect both males and females. STDs can cause serious health problems if they are not treated. If you or someone you know suspect you have an STD, seek medical attention. Some common STDs are described here. Chlamydia (kluh•MI•dee•uh) is a common sexually transmitted disease. It is caused by bacteria. Chlamydia is the most often reported bacterial STD in the United States. It is estimated that there are 2.8 million cases in the U.S. each year. Chlamydia is transmitted from person to person through sexual relations. The greater the number of sexual partners a person has, the greater the risk for the infection. Chlamydia can also be passed from an infected mother to her baby during childbirth. Chlamydia is often called a "silent" disease because most infected people don't show any symptoms. A person can have it and not know about it. If symptoms do occur, they include genital discharge and pain when urinating. Untreated chlamydia can cause pelvic inflammatory disease in females. This can cause infertility. Chlamydia can also cause infertility in males. If left untreated, it can affect the reproductive organs, urethra, and anus. Chlamydia can be cured with antibiotics. However, reinfection is common if sexual partners have not been treated. Abstinence from sexual activity is the only sure way to prevent chlamydia. Genital herpes (HER•peez) is an STD caused by viruses. It causes painful blisters on the genital area. It is transmitted by skin-to-skin contact. Sexual relations do not have to take place for herpes to be transmitted. People can have herpes for many years and not know it. There may not be any obvious symptoms. Sometimes, though, there are outbreaks of painful sores and blisters. Even when the blisters go away, the virus is still in the body. A person with herpes can infect another person even if the infected person has no blisters or sores. Symptoms also include pain in the lower genital region and genital discharge. Severe symptoms include fever and swollen glands. There is no treatment that can cure herpes. There are medications that help to reduce the number of outbreaks. They also might prevent outbreaks. Other medications might reduce the possibility of transmission to sexual partners. Abstaining from sexual contact is the only sure way to prevent transmission of genital herpes.

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Genital warts are growths or bumps in the genital region caused by certain types of human papillomavirus or HPV. HPV is the most common sexually transmitted infection in the United States. About 6 million people become infected each year. There are more than 40 types of HPV. They infect the genital areas of both males and females. HPV is passed through genital contact. Sexual intercourse does not have to occur for the virus to be transmitted. It can be passed to another person whether or not symptoms are present. HPV is another "silent" disease. Most people don't develop symptoms or health problems. In 90 percent of cases, the immune system clears the body of the virus in about two years. In some cases the body does not clear the infections. Then genital warts may appear. Warts may appear as a small bump or several bumps. On rare occasions, warts appear in the throat. Cervical cancer and cancers of other reproductive organs can also be caused by HPV. There are vaccines that can protect against the most common types of HPV. When taken by girls and women ages 11 through 26, the vaccines can protect against genital warts and most cervical cancers. When males ages 9 through 26 take the vaccines, they may be protected against genital warts and anal cancers. Condoms may also lower the risk of transmitting HPV. They may also lower the risk of genital warts and cervical cancer. However, condoms do not cover all of the areas that can be infected. So, condoms do not fully protect against HPV. As with all other STDs, abstinence is the only sure way to prevent infection with HPV. Pubic lice ("crabs") are parasites. They are usually found in the pubic or genital area of people. Pubic lice have six legs. Two of the legs look like the claws on a crab. That's how they got their nickname "crabs". Pubic lice are usually transferred from one person to another through sexual contact. They are very contagious. They can be spread through contact with clothing, bed linens, or towels if these articles have been used by someone with pubic lice. Pubic lice cause itching around the genitals. You might also notice eggs or nits attached at the base of a shaft of hair. These are small and might be difficult to see without a magnifying glass. There are a number of over-the-counter medications to kill pubic lice. These include lotions and shampoos. When using these products, it is important to follow the directions exactly. It is also important to kill lice remaining on clothing, bedding, or towels to prevent re-infestation. Items should be washed in hot water and dried in a hot dryer cycle. Items that cannot be washed should be dry cleaned. If items cannot be cleaned by any of these methods, they should be sealed in a plastic bag for two weeks to kill the lice. Trichomoniasis (TREE•koh•moh•NI•ah•sis) or "trich" is an STD caused by the protozoan Trichomonas vaginalis. It is a very common STD. It is considered to be the most common curable STD. It is estimated that 3.7 million people in the United States have the disease. The parasite is passed from person to person during sexual relations. Most people who have trichomoniasis don't know they have it. It is a silent disease. However, some people do have symptoms. Those symptoms include vaginal discharge and discomfort during urination. Irritation or itching in the genital area can also be symptoms. If left untreated, trichomoniasis can last for months or years. Having trichomoniasis can increase the chance of getting other STDs. Trichomoniasis can be treated and cured with prescription antibiotics. About 20 percent of the people who are cured of trichomoniasis are reinfected within three months. This is caused by having sexual relations with a partner who has not been cured.

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Gonorrhea (gahn•uh•REE•uh) is a bacterial STD that affects the mucous membranes of the body. Most often it affects the genital area. It is a very common disease. It is estimated that 700,000 people in the United States get gonorrhea every year. The highest infection rates are among sexually active teens and young adults. Gonorrhea is caused by having sexual relations with someone who has the disease. In some cases, mothers can pass the bacteria to their baby during childbirth. Even if a person has been treated for the disease, they can easily become reinfected. This can happen by having sexual relations with someone who has the disease. Some men with gonorrhea do not have any symptoms. Those who do, generally have a thick yellowish discharge from the genitals. They will also have a burning sensation when urinating. Most women with gonorrhea don't have symptoms. If a woman does have symptoms, they are usually mild. The symptoms are often mistaken for a vaginal or bladder infection. If not treated, gonorrhea can cause serious and permanent health problems. It can spread to other parts of the body such as the joints and heart. These conditions can be life-threatening. Women who are not treated can become infertile. Gonorrhea can be treated and cured with antibiotics. Syphilis (SIH•fuh•luhs) is a bacterial STD that can affect many different parts of the body. Syphilis is passed from one person to another by contact with a syphilis sore. Transmission happens during sexual relations. A pregnant woman can pass syphilis to her baby. Syphilis cannot be spread through contact with objects such as toilet seats, doorknobs, bathtubs, shared clothing, swimming pools, or hot tubs. The symptoms of syphilis change as the disease progresses. In the first stage painless sores appear at the place of infection. If left untreated, the disease progresses into the second stage. In this stage, a severe body rash occurs. There may also be fever, swollen lymph glands, sore throat, patchy hair loss, headaches, weight loss, muscle aches, and fatigue. During the later stages of syphilis, the infection moves throughout the body. It may damage the brain, nerves, eyes, heart, blood vessels, liver, bones, and joints. If a person is in the early stages of syphilis, a cure is possible. One injection of penicillin will cure a person who has been infected for less than a year. If a person has been infected longer than a year, multiple injections are needed. Bacterial vaginosis (BV) is the most common STD affecting females between the ages of 15 to 44. Scientists don't know how BV is spread. It occurs in females who are sexually active. Females who are not sexually active rarely get BV. Having BV increases the risk of getting other STDs. Symptoms of BV include: a white or gray vaginal discharge, pain, itching, or burning in the vagina, a strong odor, and a burning feeling while urinating. BV is treated with antibiotics. To avoid BV, practice abstinence from sexual activity. Douching should also be avoided. It can spread the bacteria that causes BV. Pelvic inflammatory disease (PID) is an infection affecting females. It can be treated with antibiotics. The symptoms of PID may be mild. Some female have no symptoms. If they do occur, symptoms can include: pain in the lower abdomen fever unusual discharge and bad odor from the vagina pain or bleeding during sex burning sensation during urination bleeding between periods. PID can damage reproductive organs if it is untreated. Having the disease can result in the inability to get pregnant. A female with untreated PID may also have pelvic/abdominal pain throughout her life.

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The media is full of messages showing sexual activity as exciting. Those messages never mention the risk associated with sexual activity. Those risks include the spread of STDs or an unplanned pregnancy. Ads also don't show the social and emotional problems that can result from becoming involved in a serious relationship while a young teen. Acquiring an STD can affect the rest of a person's life. Some cannot be cured. Having genital herpes cannot be cured. A person with this disease needs to be cautious throughout their life to avoid spreading the disease to others. The only 100 percent effective way to avoid STDs is to abstain from sexual activity. Deciding to say no to sexual activity may be a difficult decision to make. Some teens face pressure from friends to become sexually active. Choosing friends with similar values can make saying no easier. If abstinence is not an option, a condom should be used. A condom can prevent the spread of STDs if used correctly. Most STDs are transmitted through skin-to-skin contact or through the exchange of body fluids. If used correctly, condoms prevent skin-to-skin contact and the exchange of body fluids. A person who suspects that he or she may have an STD should seek medical help right away. If left untreated, STDs can cause permanent damage to the reproductive system and other serious problems. If telling parents isn't safe, a trusted adult can help understand what options are available. Free clinics are open in many cities that can treat STDs free-of-charge. Other Ways to Prevent STD Risk It's normal for teens to have sexual feelings. Puberty releases hormones that cause these feelings. Acting on them can have serious consequences. Some teens may get STDs, and some may experience unplanned pregnancies. Teens give several reasons for becoming sexually active. Some of the top reasons are listed below. They include: Peer pressure. Some teens may tell others that "everybody's doing it." Learn the facts. Less than 4 percent of all teens under the age of 13 are sexually active, according to the CDCs 2017 Youth Risk Behavior Surveillance Survey. To avoid this pressure, choose friends who share your values and support your decisions. Dating partner pressure. Communicate your limits to a dating partner when you begin dating. If the dating partner persists, use refusal skills to say no a dating partner who wants to become sexually active. For example, try responding to a dating partner who says, "If you really cared about me, you would," by saying, "If you really cared about me you would respect my decision." Media images showing sexual activity as exciting. Remember that media images are fiction. These stories may be appealing. They do not show the consequences of sexual activity, such as getting STDs and unplanned pregnancy. They also do not show the emotional side of becoming sexually active. This can include feeling committed to just one person or feeling controlled by a dating partner that you no longer wish to date. Being under the influence of alcohol or drugs. Avoid using alcohol or drugs. It's illegal for teens to use these substances. Using alcohol or drug can weaken a teen's defense against unhealthful influences. Finally, consider going on group dates. Group dates can include several teens. This type of dating gives teens time to learn about the type of person they like without the pressure to become too serious.

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HIV and AIDS are diseases that attack the immune system. HIV attacks lymphocytes called T cells. When it attacks a T cell, it replaces the cell's genetic information with its own genetic information. Then it begins to multiply. As more T cells are taken over, the immune system weakens. Eventually, the T cell count drops so low that the immune system can no longer protect the body. When this happens, AIDS develops. The art in the Lesson Resources panel describes how HIV attacks the immune system. AIDS continues to weaken the immune system. When AIDS is present in the body, the likelihood of developing an opportunistic infection increases. Opportunistic infections rarely occur in a healthy person. For example, many people with AIDS develop a type of pneumonia that can cause death. Drugs can help delay the onset of AIDS. However, there is no cure. People with AIDS will eventually die from diseases that a healthy immune system could have resisted. In the United States, about 1.1 million people are living with HIV. About 160,000 of those people are unaware that they have HIV. This group accounts for about 40 percent of all new HIV infections.

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How HIV is Spread You cannot get HIV through casual contact with a person who has the virus. You cannot get HIV through casual contact with a person who has the virus. HIV circulates through the body in infected blood and other body fluids. Body fluids that can transmit HIV include fluid from the vagina, breast milk, and semen. Semen is the fluid that carries sperm. There are several ways these fluids spread from one person to another. Engaging in sexual intercourse with an infected person. The most common way HIV spreads is through sexual intercourse. Having any form of sexual intercourse with an infected person can spread HIV. HIV circulates in the bloodstream and in other body fluids. During sexual activity, semen and vaginal fluids are transferred from one person to the other. HIV can be transferred in these fluids. The virus circulates in the body even before it destroys the immune system. People can have the virus and not know it. This makes it extremely risky to have sexual intercourse outside of a monogamous relationship. People with multiple partners are at the greatest risk of getting the virus. Only one incident of sexual activity with an infected person can spread the virus. Using a contaminated needle. Drug users can get HIV from a needle that has already been used by an infected person. A tiny drop of blood left on a needle is all it takes to transmit HIV to another person. Needles used for tattooing and piercing can also be contaminated. They, too, can transmit the virus. People who use needles to take medication for diabetes or other illnesses should do so under the care of a medical professional. Other ways HIV is spread. HIV can be spread from a pregnant woman with HIV to her developing baby. It can be transmitted to the child during birth or during breast feeding. Certain drugs can reduce the rate of transmission of HIV to the unborn child during pregnancy. In the years before it was known that HIV caused AIDS, some people were infected during blood transfusions through a contaminated blood supply. However, since 1985, all blood is screened for HIV. The blood supply in the United States is considered to be extremely safe from the virus. How HIV is NOT Spread Remember that HIV can only be spread through specific infected body fluids. The HIV virus cannot survive for long outside these specific body fluids. HIV cannot be spread by: Breathing the air near an infected person Being bitten by a mosquito that has bitten an infected person Touching the tears of an infected person Touching the sweat of an infected person Touching objects touched by someone with HIV Shaking hands with an infected person Hugging an infected person Swimming in a pool with an infected person Sharing utensils with an infected person Donating blood Using the same shower, bathtub, or toilet as an infected person Sharing sports equipment with an infected person It is not necessary to avoid people with HIV or AIDS. You cannot get sick just by being around them. They need your friendship and respect just like other people.

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Fighting AIDS MAIN IDEA AIDS is a worldwide problem. The World Health Organization (WHO) estimated that in a recent year that 34 million people worldwide were infected with HIV. In that same year 1.8 million people died from AIDS. Recent estimates by the Centers for Disease Control and Prevention (CDC) state that 12 million people in the United States are infected with HIV. Young people ages 13-29 account for 39 percent of the new HIV infections in recent years. CDC also believes that 20 percent of the people with HIV do not know they have it. CDC is the government agency that protects and promotes the health of the people of the United States through research and education. Knowledge and abstinence until marriage are the best weapons against HIV and AIDS. Around the world, scientists, doctors, and others are working to educate people about the disease. When people know how it is spread, they can take measures to avoid becoming infected. Detecting HIV Earlier you learned that a person can be a carrier of HIV without having AIDS. A carrier can pass the virus to others. The only way to learn whether a person has HIV or AIDS is to do laboratory tests using the person's blood. The CDC has made two recommendations to identify whether a person has HIV or AIDS. The CDC made these recommendations because about 1 in 7 people in the U.S. have HIV and are unaware that they have the disease. The recommendations are: Every person between the ages of 13 and 64 be tested once for HIV. This test should be done as part of a routine medical exam. Every person being treated for an STD should also be tested for HIV. The person should be told why they are being tested for HIV. Testing should only take place if the person agrees to it. Laboratory testing is the only way to show whether the virus antibodies are present. However, if a person was recently infected, the virus antibodies may not show up in a lab test. The CDC recommends that people who are in a high-risk category should be retested in three months. The CDC also provides information on how and where to get tested. Resources for testing include your personal doctor, medical clinics, substance abuse programs, community health centers, and hospitals. To learn where you can get tested in your community, use these resources: Call 1-800-CDC-INFO (232-4636) Visit gettested.cdc.gov Text your zip code to KNOW IT (566948) Treating HIV and AIDS Receiving a diagnosis of HIV is a life-changing event. Researchers are continued to search for a cure for HIV/AIDS. At this time, a cure does not exist. Therapies do exist that reduce the virus in the body. Drug therapy called antiretroviral therapy, or ART is prescribed to treat HIV. ART includes taking a series of medications to reduce the viral load in the body. ART therapy has been very successful. In some people on ART, the amount of HIV in the bloodstream has been reduced to levels that cannot be detected. This does not mean that the person does not have HIV any longer. If ART is ended, the virus will begin to multiply again. Fighting HIV infection is costly and difficult. So, scientists and educators work hard to keep people from getting HIV in the first place. Knowledge and abstinence are still the best weapons in the fight against HIV and AIDS.

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Stopping the Spread of HIV Work to develop drugs that elminate the disease continue but progress has been made. Scientists are working to develop a vaccine to prevent the spread of HIV. Some drugs that have been developed to fight the infection have reduced the level of HIV in the blood of some carriers. At this time a vaccine is not available to prevent the spread of HIV. Until a vaccine is available, the best way to prevent HIV is to avoid high-risk behaviors. There are three main ways to avoid HIV and AIDS: Practice abstinence. Abstinence is consciously choosing to not participate in high-risk behaviors. Avoiding sexual activities until marriage is one type of abstinence. People who participate in sexual activity expose themselves to risks. They may not know whether their partner has an STD. They may not know whether their partner has HIV or AIDS. The more sexual partners a person has, the greater their risk of getting an STD such as HIV. Avoid drugs and alcohol. Using drugs and alcohol can make a person lose their ability to make good decisions. When their judgment is impaired, they are more likely to engage in risky behaviors. The risky behaviors might include sexual activity. Avoid sharing needles. Shared needles can carry enough blood to inject HIV into your blood stream. This includes needles used for injecting drugs or for tattoos or piercing. Sharing needles exposes you to any diseases the previous user has. The only sure way to avoid getting HIV is to avoid contact with sources of the virus. Abstaining from sexual activity until marriage and not injecting drugs or sharing needles are ways to avoid contact with the virus. Avoid peer pressure to engage in these activities. Talk to a parent or trusted adult if you are being pressured. Find new friends if you need to. Find friends who think the way you do, who share your values, and who respect your decisions. Make responsible choices. It could save your life.

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Your head aches. Your nose runs. Your eyes are watery. You have a cough. You have a sore throat. You have a fever. You have a cold. You take some cold medicine and rest for a few days. Your cold is gone. It hasn't always been this easy to recover from an illness or disease. Scientists study diseases and illnesses and try to come up with treatments. In some cases, they have come up with medicines that prevent diseases. A cold is one type of disease. A disease like a cold that can spread from one person to another is called a communicable disease. Communicable diseases are caused by pathogens. You probably know them as germs. Another category of disease is a noncommunicable disease. Germs are all around us. Some germs are not harmful. When a harmful germ, or pathogen, enters your body, it can multiply and cause an infection.

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Pathogens are not all alike. However, all pathogens can cause disease. There are four main types of pathogens: viruses (VY•ruh•suhz), bacteria (bak•TIR•ee•uh), fungi (FUHN•jy), and protozoa (proh•tuh•ZOH•uh). Viruses are so tiny they can only be seen with a special microscope. Viruses are not alive. They are usually made up of genetic material and protein. Some strains, or types, of viruses are not harmful. Other types can cause diseases such as the common cold, flu, upper respiratory infections, and measles. Most infections caused by viruses cannot be cured with antibiotics. The most harmful viruses can cause serious diseases. AIDS and hepatitis are serious diseases caused by viruses. AIDS is an immune system disorder. Hepatitis is a disease of the liver. Bacteria are everywhere. Some of these simple one-celled organisms are helpful to humans. For example, the bacteria in your digestive tract help you break down the food you eat. Other bacteria live on your skin and help prevent harmful bacteria from infecting you. Some bacteria, though, is harmful. Harmful bacteria can cause diseases such as pneumonia and strep throat. Most infections that are caused by bacteria can be treated with antibiotics. Fungi cannot make their own food. So they must break down other organisms and absorb their nutrients. Most fungi are harmless to humans. Mushrooms, for example, are fungi. Some mushrooms are safe for humans to eat. Molds and yeast are also fungi. Fungi like to live in warm and moist places. They can cause a variety of diseases. Athlete's foot and ringworm are caused by fungi. Fungi can also cause serious lung infections. Protozoa are also one-celled organisms but are more complex than bacteria. Some protozoa, called parasites, attach themselves to healthy cells. They rob the cell of nutrients, but they don't kill the cell. Some protozoa cause serious illnesses in humans. One of the most well-known and deadly diseases caused by protozoa is malaria. Malaria is found in tropical regions. It is spread to humans by infected mosquitoes. If an infected mosquito bites a person, the protozoa are transferred into the body through the skin. The figure located in the Lesson Resources panel shows some kinds of pathogens and lists the diseases they cause.

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How Pathogens Spread How can you keep from being infected by a communicable disease? Well, to understand how to avoid becoming infected, it's important to understand how pathogens are spread. There are four main ways pathogens are spread. Direct contact One of the most common ways pathogens are spread is by physically touching another person. For example, if someone with a cold sneezes into his right hand and then you shake hands with him; you will likely get cold pathogens from him. Shaking hands with him passes along the germs that are on his skin. Washing your hands often with soap can help stop the spread of pathogens. Some pathogens are spread through contact with infected blood. People can come into contact with infected blood by injecting drugs using a needle that someone else has used. Dirty needles used for tattooing or piercing can also spread pathogens. It is also possible for the blood of an infected person to infect someone else if the blood comes into contact with broken skin. Some pathogens are spread through sexual contact. Abstinence is the best way to prevent sexually transmitted diseases. Indirect contact If someone sneezes or coughs, pathogens are spread through the air. It is important to use tissues to cover your nose when you sneeze and your mouth when you cough. Pathogens are also spread when people share certain items. Drinking glasses and eating utensils should never be shared. Other items such as toothbrushes and razors should not be shared. Contact with animals or insects Animals and insects can spread pathogens. An organism that transmits pathogens is a vector. If an animal is sick with rabies, for example, that animal can spread rabies if it bites someone or another animal. Insects spread many diseases. For example, infected deer ticks can spread Lyme disease. Infected mosquitoes can spread malaria or West Nile virus. Using insect repellent when you go outdoors can help protect you from insect bites. Contaminated food and water Bacteria that cause food poisoning can be spread through contaminated food or water. If the contaminated food or water is eaten or drunk, the pathogens spread into the individual. If food is undercooked or improperly stored, pathogens can grow. The pathogens can cause illness. Illnesses caused by contaminated foods are called foodborne illnesses. To help prevent foodborne illnesses, make sure meat is fully cooked. Undercooked meat may contain bacteria that will make you ill. Remember to properly store foods that can spoil. This includes dairy products and meat. You should also wash fruits and vegetables. Many food packages say the product has been washed. However, it never hurts to wash it yourself. Meat, poultry, fish, and eggs need to be handled carefully. Bacteria from raw meats and eggs can spread on your food preparation surface. Keeping your food preparation area clean is very important. You should always wash knives and surfaces that meat, poultry, fish, and eggs have touched. Use warm, soapy water to clean food preparation surfaces.

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Stopping the Spread of Pathogens MAIN IDEA Practicing certain healthy behaviors can stop the spread of pathogens. Although you can't completely stop the spread of pathogens, you can protect yourself and others from the spread of pathogens. Good personal hygiene is one of the best ways to help stop the spread of pathogens. You can also help stop their spread by eating nutritious foods and getting enough sleep. Engaging in regular, physical activity will also help your body fight pathogens. Keep your environment, the space around you, clean. This will also keep down the number of pathogens. Stopping the spread of pathogens will help to protect your health and the health of others. Protecting Yourself So, what can you do to protect yourself from pathogens? In addition to the tips mentioned above, follow these guidelines to help keep yourself from getting sick. Keep your distance from people who are sick with a communicable disease. Be especially careful if they are still contagious. Do not share eating or drinking utensils or toothbrushes or other personal hygiene items. Wash your hands thoroughly in warm soapy water before preparing or eating food. It is important to wash after using the bathroom, playing with pets, and visiting a sick person. It is also necessary to wash after touching trash or garbage or other sources of pathogens. Keep your hands and fingers away from your mouth, nose, and eyes. Don't bite your fingernails. Handle and prepare food safely. This is especially important for meats, fish, and poultry. Eggs should be handled carefully, too. Meats, fish, poultry, and eggs should be cooked thoroughly. Wash vegetables and fruits before eating. Wash counters thoroughly with paper towels or a clean sponge or cloth. If you use a sponge or cloth, clean them thoroughly and frequently. Using sponges and cloths repeatedly can spread more germs than they remove. Keep your environment clean. Empty the trash often. Keep the trash cans clean. Clean up after your pets. Another way to maintain good health is to practice healthy lifestyles. If you are exposed to pathogens, a healthy lifestyle can help you avoid getting sick. These healthy lifestyle practices include the following. Eat a balanced diet. Bathe or shower regularly using soap. Be sure to wash your hair using shampoo. Avoid tobacco products, alcohol, and other drugs. Get 8-9 hours of sleep every day. Rest when you are sick. Check with parents or guardians to make sure your immunizations are up to date. Manage your stress well. Learn ways to relieve your stress. Too much stress can weaken your immune system and make you more vulnerable to communicable diseases. Get regular physical checkups. Talk with your doctor if you have questions.

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Protecting Others You might be carrying pathogens and not realize it. You may have a communicable illness that hasn't shown symptoms yet. If you come into contact with others, you can easily spread the pathogens. Help protect the people you come into contact with. Think ahead and follow these healthful behaviors. If you are sick, stay home and away from others. Tell your parent or guardian and get medical help if you need it. If you become ill at school, let the school medical personnel know as soon as possible. Getting medical help early can keep the illness from getting too bad. It can also help keep it from spreading. When you sneeze or cough, cover your mouth with a tissue. Only use the tissue once. If you don't have a tissue, what should you do? Sneeze or cough into the crook of your elbow. This helps to keep pathogens from spreading. Wash your hands immediately after you sneeze or cough. If you have a prescription to take medication, follow the directions exactly. Take all of the medicine you are supposed to take. If you stop taking the medicine before you are supposed to, you might become sick again.

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