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1 CHAPTER 17 Immunity and Disease LESSON 1 Diseases What do you think? Read the two statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you ve read this lesson, reread the statements to see if you have changed your mind. Key Concepts Why do we get diseases? How do the two types of diseases differ? Before Statement After 1. Some diseases are infectious, and others are noninfectious. 2. Cancer is an infectious disease. Disease Through History Thousands of years ago, a doctor might have treated a disease by scraping a person s skull with a rock until a hole formed. The doctor made the hole in the skull to let the illness escape. Archaeologists know this because they have discovered skulls with smooth holes in them. Bone growth around the holes shows that people lived after these holes were made. This treatment may sound strange today. However, it was an accepted treatment for disease thousands of years ago. Today we know that many diseases are caused by bacteria and viruses. Disease-causing agents, such as bacteria and viruses, are called pathogens. Pathogens have always caused illnesses. However, it has been only during the last few hundred years that scientists have understood the relationship between pathogens and diseases. Before then, little was known about disease and immunity, and superstitions were common. Early Research on Diseases During the eighteenth and nineteenth centuries, doctors learned a lot about the causes and treatment of diseases. The research and experiments performed by scientists such as Edward Jenner, John Snow, and Anton van Leeuwenhoek saved many lives. Discuss Main Ideas Read the first paragraph about disease. Then take turns with a partner saying something about what you have learned. Repeat this process with the other paragraphs in this lesson. 1. Identify List two types of pathogens. Reading Essentials Immunity and Disease 283

2 First Vaccination In 1796, Edward Jenner developed the first vaccination. A vaccination is a procedure that helps the body defend itself against disease. Jenner knew that women who milked cows often got a mild disease called cowpox. However, these women did not get smallpox, a deadly disease related to cowpox. Jenner, who was a doctor, cut the arm of a young boy and placed pus from a cowpox sore in the cut. Two weeks later, Jenner infected the boy with smallpox. Like the women who milked the cows, the boy never got sick from smallpox. Although the smallpox vaccine saved many lives, people did not understand why or how it worked. 2. Explain How did Dr. Jenner prevent people from getting smallpox? 3. Evaluate Why was the work of Dr. Snow important? Visual Check 4. Locate How did Snow use his map to identify the source of the cholera outbreak? Connecting Disease with a Source In the mid-1800s, people realized that there was a connection between pathogens and disease. Cholera is a disease of the intestinal tract caused by a bacterium. Dr. John Snow connected the disease to a bacterium he found in water. He did this by tracking the origin of a cholera outbreak on a map similar to the one below. Using the map, Snow tracked the outbreak to a single water pump in the city of London. He had the pump closed. Almost immediately, the number of new cholera cases decreased. When Snow looked at the water, he saw a microscopic organism that he thought caused the disease. Not everyone agreed with Snow, but people were beginning to think that pathogens did exist. Cholera death Water pump Contaminated water pump 284 Immunity and Disease Reading Essentials

3 The Development of Microscopes One of the reasons people were slow to accept the idea of pathogens is because people could not see the pathogens. However, the development of microscopes changed that. In the late 1600s, Anton van Leeuwenhoek (LAY vun hook) made one of the first microscopes. Using the microscope, he observed pond water and saw moving organisms. Van Leeuwenhoek had discovered bacteria. Because he did not share how he made the lenses, bacteria were not observed again until the nineteenth century. Connecting Bacteria to Infections As first, scientists thought that wounds caused bacteria to appear. Louis Pasteur experimented with bacteria in the mid-1800s. He realized that this idea was backwards. Instead, bacteria caused the tissue in the wound to decay. He found that he could kill bacteria in boiling liquids. Pasteurization is the process in which a food is heated to a temperature that kills most harmful bacteria. The pasteurization process used today is based on the work of Pasteur. Joseph Lister used Pasteur s discoveries to make surgery safer for patients. He found that a substance called carbolic acid killed bacteria. He developed a system of spraying carbolic acid throughout an operating room during surgery. Infection and death from surgery decreased greatly. In the late 1800s, doctors improved on Lister s idea. They used carbolic acid to sterilize tools before surgery. They also used steam to sterilize the clothes and linens used during surgery. Sterilization completely kills the bacteria. Discovering Disease Organisms In 1867, Robert Koch developed a set of rules that could be used to find out if certain bacteria caused an illness. The research based on these rules convinced most scientists that bacteria were disease-causing pathogens. Koch s rules are described in the following figure. 5. Explain How did Lister make surgery safer? Visual Check 6. Describe According to Koch s rules, what must happen when a pathogen is placed in a healthy animal? 1 The bacterium must be found in all organisms suffering from the disease, 2 The bacterium must reproduce in the lab. 3 A sample of the newly grown pathogen must cause the illness when injected into a 4 When the suspected pathogen is removed from the infected animal and but not in healthy organisms. healthy animal. grown in the lab, it must be identical to the original pathogen. Reading Essentials Immunity and Disease 285

4 Human Diseases and the Pathogens That Cause Them Visual Check 7. Identify What pathogen causes ringworm? Pathogens Viruses Bacteria Fungi Protists Diseases Caused flu, colds, chickenpox, and AIDS ear infections, strep throat, pneumonia, meningitis, whooping cough, and syphilis, a sexually transmitted disease athlete s foot, ringworm, and yeast infections malaria, African sleeping sickness, and dysentery Key Concept Check 8. Explain Why do we get diseases? Bacteria aren t the only pathogens that cause disease. Viruses, fungi, and protists can also cause disease. The table above shows diseases caused by different pathogens. Pathogens can be passed through water and food and carried by insects. They can also be passed directly among people by physical contact, sneezing, coughing, or exchange of bodily fluids. Some pathogens require a host to reproduce. Types of Diseases Have you ever heard someone say, I caught a cold? The common cold is contagious. This means that the pathogens can be passed from person to person. Not all diseases are caused by pathogens. Some diseases are the result of inherited traits. Other diseases can be caused by factors such as your environment and the choices you make about diet, exercise, and sleep. Infectious Diseases Diseases caused by pathogens that can be transmitted from one person to another are infectious diseases. For example, flu and cold viruses can be passed through direct contact, such as by shaking hands. The human immunodeficiency virus (HIV) can pass to others through the exchange of blood or other bodily fluids. HIV causes acquired immunodeficiency syndrome (AIDS), a disease that attacks the body system that fights pathogens. The protist that causes malaria is transferred by a vector. A vector is a disease-carrying organism that does not develop the disease. The vector for malaria is a certain type of mosquito. The mosquito bites an animal that has the protist in its blood. The protist enters the mosquito s saliva, but the mosquito does not develop malaria. When the mosquito bites another animal, the protist moves into that animal s blood. 286 Immunity and Disease Reading Essentials

5 Noninfectious Diseases A disease that cannot pass from person to person is a noninfectious disease. For example, you cannot catch lung cancer from a person who has lung cancer. Pathogens do not directly cause noninfectious diseases. There are two common causes of noninfectious diseases: genetics, or traits inherited in your DNA from your biological parents, and environmental conditions, including lifestyle choices. A person who has a genetic trait might develop a noninfectious disease because of environmental conditions. It is the combination of genetics and environment that causes the disease to develop. Childhood Diseases Noninfectious diseases that affect children are mainly a result of genetics. Cystic fibrosis is a genetic disease. It causes the body to produce mucus that is thicker than normal. This affects breathing and other body functions. The gene that causes cystic fibrosis is recessive. This means a child must inherit this recessive gene from each parent to be affected by cystic fibrosis. The parents, called carriers, do not have to have the disease. For many children with genetic disorders, environmental conditions can make the disease worse. A poor diet, air pollution, and lack of exercise make the symptoms of cystic fibrosis worse. Other Diseases Many noninfectious diseases that affect adults are mainly a result of environmental causes and life choices. For example, an unhealthful diet, obesity, a lack of regular exercise, and smoking cause most cases of heart disease. Osteoporosis is a disease in which bones become weak and less dense. People inherit a tendency to develop osteoporosis. However, years of poor lifestyle choices, such as an unhealthful diet, lack of calcium and vitamin D, smoking, and a lack of exercise can lead to weakened bones. Cancer Tumors form when cells reproduce uncontrollably. Cancer is a disease in which cells reproduce uncontrollably without the usual signals to stop. For example, lung-cancer tumors form in the lungs. The tumors decrease normal lung function. People can inherit forms of genes that make them more likely to develop lung cancer. But if they are not exposed to harmful environmental conditions such as poor air quality and smoking, they might not develop lung cancer. Make the following two-tab book, then use it to compare infectious diseases and noninfectious diseases. Infectious Diseases Noninfectious Diseases 9. Identify List some causes of noninfectious diseases. Key Concept Check 10. Explain How do infectious diseases and noninfectious diseases differ? Reading Essentials Immunity and Disease 287

6 Mini Glossary cancer: a disease in which cells reproduce uncontrollably without the usual signals to stop infectious disease: a disease caused by pathogens that can be transmitted from one person to another noninfectious disease: a disease that cannot pass from person to person pasteurization: the process in which a food is heated to a temperature that kills most harmful bacteria pathogen: a disease-causing agent, su ch as a bacterium or a virus vector: a disease-carrying organism that does not develop the disease 1. Review the terms and their definitions in the Mini Glossary. Write a sentence that uses the following terms: cancer, noninfectious disease, and pathogen. 2. Complete the chart below by filling in one discovery for each century that helped scientists understand more about pathogens and disease. The last frame has been done for you. Discoveries in the 1600s Discoveries in the 1700s Discoveries in the 1800s What do you think Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind? ConnectED Dr. John Snow made a connection between cholera and the bacterium that causes it. 3. Reread the paragraphs about infectious and noninfectious diseases. Write one fact about each type of disease that you learned from the paragraphs. Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson s resources. END OF LESSON 288 Immunity and Disease Reading Essentials