Global Deaths by Infectious DiseasesDisease

Respiratory Infections

AIDS

Diarrheal Diseases

Tuberculosis

Malaria

Deaths (in millions)

Source: World Health Organization. WHO global burden of disease (GBD) 2004 estimates (revised).

4.2

2.0

2.2

1.5

0.9

Environmental Health 261

You encounter biological hazards every day. They are in the air you breathe, the food you eat, and the water you drink. Your body is con-stantly working to fight these pathogens off. Usually, your body wins—but not always. In fact, diseases caused by biological hazards are the second-leading cause of death worldwide. Because of this, scientists around the globe are working on ways to identify, treat, and prevent these diseases.

Infectious Disease Infectious diseases are spread by direct human contact,

through contaminated food and water, and by animals.

Infectious diseases are diseases caused by a pathogen, such as a virus or a bacterium. Pathogens are biological hazards. Globally, infectious diseases account for about 30 percent of all deaths each year—nearly 18 million people. About three fifths of these deaths result from just five types of diseases. Figure 6 lists these diseases and the estimated number of deaths they caused in 2004.

Disease Transmission Infectious diseases spread through the human population in different ways. For example, pathogens can be spread by humans, water or food, or by other organisms.

▶ Humans Some diseases are spread directly from one human to another. For example, touching, biting, sexual intercourse, contact with bodily fluids, and inhaling expelled droplets can all spread disease. HIV—the virus that causes AIDS—can be transmitted when a person comes into contact with the blood or body fluids of an infected person. Tuberculosis (TB) is spread through droplets in the air. People who are infected with TB release bacteria-laden droplets when they cough, sneeze, speak, and spit. If a person nearby breathes in the droplets, he or she may become infected with TB.

LESS

ON 2

FIgure 6 global Infectious Disease The five types of diseases listed killed an estimated 10.8 million people in 2004. AIDS alone killed about 2 million people, roughly equal to the entire population of Arkansas.

• Describe how infectious diseases spread.• Explain why emerging diseases are important to

monitor and control.• Differentiate between social hazards that are

lifestyle choices and those that cannot be controlled.

Reading Strategy As you read each section under a large blue heading, jot down the key points. Using the key points, write in your notebook a summary of what you have read.

Vocabulary infectious disease, emerging disease

guiding Question: How do biological and social factors in the environment affect human health?

Biological and Social Hazards

9.2 Lesson PLan Previewreal World Students investi-gate local drinking water and wastewater treatment.Differentiated Instruction Help less proficient readers outline the lesson.

9.2 resources Paper and Pencil Activity, Tracking an Outbreak • Bellringer Video, Swine Flu Could Be a Global Pandemic • Lesson 9.2 Worksheets and Assessment • Chapter 9 Overview Presentation

FOCUS Watch the ABC News video Swine Flu Could Be a Global Pandemic. Have students use their own experi-ences to talk about how the spread of H1N1 virus was controlled in the months after the video was made.

▶ Water or Food Some pathogens spread when people consume con-taminated water or food. For example, Vibrio cholerae, the bacterium that causes cholera, is a waterborne pathogen. Human feces that contain Vibrio cholerae contaminate water supplies. When a person drinks con-taminated water, he or she may experience intense diarrhea and vomiting. These symptoms can lead to dehydration and even death.

▶ Other Organisms Disease can also be spread by other organisms. In these cases, the organism carries the pathogen and passes it to a person. These disease-carrying organisms, or vectors, usually do not suffer from the disease themselves. Some vectors, such as ticks and mosquitoes, trans-mit pathogens when they bite humans. For example, female mosquitoes in the genus Anopheles carry pathogens that cause malaria. A mosquito picks up the pathogen when it bites an infected person and transmits it when it bites a non-infected person (Figure 7).

Reducing Risk Infectious diseases account for almost half of all deaths in developing nations. But, in developed nations, infectious disease is less of a threat because of public health measures, such as better sanitation and access to medicine. For example, developed nations often have effec-tive water treatment facilities. Public water supplies are closely monitored and treated so that high levels of pathogens do not contaminate the water. In addition, developed nations often have adequate wastewater treatment plants. These facilities accept and treat sewage so that human wastes are not released directly into the environment.

Figure 7 Animal Vectors Female Anopheles mosquitoes can transmit the malaria pathogen when they bite. Form an Opinion DDT kills Anopheles mosquitoes. Does this fact justify spraying DDT in Africa?

Figure 8 Clean Water Supplies Clean water is a critical step toward reducing infectious diseases worldwide. Lack of clean water and basic sanitation kills nearly 2 million young children each year (nearly 5000 per day). In the inset photo, young African children collect water to bring home, unaware that it is contaminated with cholera.

262 Lesson 2

ANSWERS

Figure 7 Answers will vary, but students should justify their opin-ion whether or not DDT should be sprayed to kill mosquitoes.

Environmental Health 263

Cholera is a good example of how wastewater treatment plants help reduce the spread of disease. Because Vibrio cholerae gets into waterways through human feces, sewage contamination can lead to cholera epidem-ics. Treating sewage, therefore, helps reduce the incidence of cholera.

There are many ways you can reduce your risk of catching and spread-ing infectious diseases. For example, you should cover your nose and mouth with your sleeve or a tissue when you cough or sneeze. Then, throw the tissue in the garbage. You should wash your hands often with soap and water. If soap is not available, use an alcohol-based hand sanitizer. And if you are sick, stay home from school to avoid spreading the disease.

ReadingCheckpoint

Describe how pathogens can spread directly from one person to another.

Emerging Diseases Since new diseases are continually emerging, it is important to

know how, where, and to what extent they are spreading.

Despite our attempts to reduce and avoid disease, we are constantly bat-tling new diseases. An emerging disease is a disease that has appeared in the human population for the first time, or that has existed for a while but is increasing rapidly or spreading around the world.

The pathogens that cause emerging disease are particularly dangerous because humans have developed little or no resistance to them. In addi-tion, methods of controlling emerging diseases, such as vaccines, have not been developed.

One good example of an emerging disease is the H1N1 (swine) flu. The current strain first appeared in Mexico in March 2009. By June, it had spread to 70 nations, infecting nearly 30,000 people. At that time, the World Health Organization (WHO) declared it a global pandemic level 6—the highest level. A pandemic is an outbreak that becomes widespread and affects a whole region, continent, or the world.

Analyze and Conclude1. Infer What can you infer about how the

“virus” spread through the classroom?2. Apply Concepts How does thorough

hand washing help prevent the spread of diseases?

3. Design an Experiment Suggest a way to model the spread of a vector-borne disease.

How Do Diseases Spread? 21 3 4 65 7 8 9 Your teacher has placed a fluorescent material in the

classroom to simulate a virus. Keep track of the people and objects you touch. Then, use a UV flashlight to check for the “virus” on your hands, objects, and people you have touched since entering the classroom. CAUTION: Do not look directly at the UV light.

21 3 4 65 7 8 9 Exchange results with your classmates to determine how the “virus” spread throughout the classroom. Wash your hands with soap and warm water before leaving your classroom.

ANSWERS

Quick Lab1. The “virus” was spread throughout

the classroom by students as they touched contaminated objects with their hands.

2. Thorough hand washing washes viruses off hands. Therefore, fre-quent hand washing may prevent the spread of diseases.

3. Answers will vary, but should outline a procedure to model a vector-borne disease.

Reading Checkpoint Pathogens can spread from one person to another by touching, biting, sexual intercourse, contact with body fluids, and inhaling expelled droplets.

MRSA

Multidrug-resistant

tuberculosis

H5N1 avianin�uenzaEbola

Dengue

Diphtheria

Cholera

E. coliO157:H7

West Nile VirusE. coliO157:H7

H1N1 swine in�uenza

H1N1 swine in�uenza SARS

NORTH AMERICA

SOUTH AMERICA

ASIA

AUSTRALIA

ANTARCTICA

EUROPE

AFRICA

ARCTIC OCEAN

ATLANTIC OCEAN

INDIAN OCEAN

PACIFIC OCEAN

264 Lesson 2

The Spread of Emerging Diseases Emerging diseases may quickly spread to new regions or population centers. Therefore, it is important to understand some of the ways diseases emerge and spread.

▶ Increasing Mobility Many diseases are spreading as people become more mobile. A virus for influenza can move across continents in just a few hours if an infected person takes a long airplane flight. Whenever people or other animals move around Earth, they may be taking patho-gens along with them.

▶ Antibiotic Resistance Other diseases, such as tuberculosis, are becoming resistant to our antibiotics. That is, they can survive and grow even when we take medicines that have previously killed them. Antibiotic resistance is a result of natural selection. If a few pathogens in a popula-tion are either naturally resistant or develop resistance to an antibiotic, they will survive when exposed to the drug. The rest of the population will die, but a few resistant organisms may then reproduce and create new populations of resistant pathogens.

▶ A Changing Environment By altering their environment, people may spread emerging diseases. For example, when people cut down forests, they may come into contact with animals that carry pathogens. These animals, and their pathogens, may have been previously contained inside the forest environment.

Figure 9 emerging Diseases The map shows where some emerging diseases have recently appeared. Some of these diseases, such as cholera and diphtheria, are not new, but have appeared in new areas. Others, like SARS and MRSA are more recent threats.

What is the relationship between environmental health and our own health?Interpretation Have students read the information about the spread of emerging diseases. Then have students write a short story that involves human actions that affect or are affected by the spread of an emerging disease.

BIG QUESTION

265

FIGURE 10 Response to Emerging Disease Researchers work with the H1N1 virus at a CDC lab in Atlanta. The inset shows a colorized micrograph of the H1N1 virus.

Climate change is another way our changing environment may encourage the spread of disease. If global temperatures continue to rise, tropical diseases such as malaria and cholera could expand into new, formerly cooler areas.

Responding to Emerging Diseases Emerging diseases can surface and spread quickly. As a result, having a reliable response system in place is a necessary step toward maintaining global health. Currently, international and government agencies and organizations work together to help monitor, respond to, and control the spread of emerging diseases.

▶ International Response The World Health Organization (WHO) is an international group that helps respond to emerging diseases. It has networks of organizations, agencies, labs, and medical centers that moni-tor world health events. When an emerging disease is identified, WHO posts the information on the World Wide Web. Within 24 hours, a team goes to the site to assess the situation. If needed, WHO will then help coordinate an international response.

▶ National Response Individual nations also help respond to emerg-ing diseases. In the United States, the Centers for Disease Control and Prevention (CDC) is the primary national center for responding to emerging diseases. It works with international as well as other federal, state, and local organizations to develop and apply disease prevention and control measures.

For example, the CDC has taken many steps to help contain the spread of the H1N1 virus. The CDC has worked with states to develop pandemic plans. The CDC has also performed lab testing of the virus and assisted with training workshops on viral identification techniques. In conjunction with the companies that develop the seasonal flu vaccine, it has developed a vaccine against the H1N1 virus.

ReadingCheckpoint

What are three factors that influence the spread of emerging diseases?

ANSWERS

Reading Checkpoint Increased travel, antibiotic resistance, and a changing environment

266 Lesson 2

1. Review Describe one way pathogens can spread through the environment.

2. Explain Why is it important to have an interna-tional organization such as WHO coordinating responses to emerging diseases?

3. Apply Concepts Describe three social hazards that are a result of choices you make every day.

4. Explore the BIGQUESTION Do you think that modern medicine will ever eliminate biological hazards from Earth? Why or why not?

2

Social Hazards Some social hazards result from lifestyle choices a person

makes, while other social hazards cannot be controlled.

Where you live, your job, and the choices you make every day affect your health. When these factors harm your health, they are called social hazards. Some social hazards can be easily avoided, while others are more difficult. For example, you might live near an old toxic waste site that is leaking harmful chemicals into the soil. Or your job could put you into contact with harmful chemicals.

Smoking is a social hazard that can cause lung cancer. A person can avoid this risk by not smoking. Cigarette smoke irritates a person’s eyes, nose, and throat and can make asthma worse. But tobacco smoke can also affect the health of a nonsmoker when he or she breathes in secondhand smoke. Secondhand smoke is the exhaled smoke from nearby smokers mixed with smoke from a burning cigarette, pipe, or cigar. Secondhand smoke exposure has been linked to lung cancer and respiratory tract infections. While you can choose not to smoke, how much secondhand smoke you breathe in may be difficult to control, especially if you live with a smoker.

You may not think of potato chips as a hazard. But if your diet con-sists primarily of fatty foods, this is considered a social hazard. A high-fat diet can put you at risk for heart attack and stroke. The good news

is that diet, along with many other social hazards, can be reduced sim-ply by changing your behavior. You can choose to eat healthful foods. You can also choose to stay active by exercising regularly. By staying active, and eating healthfully, you may be able to avoid obesity, heart disease, and high blood pressure.

FiguRE 11 Healthy Lifestyle Choices You can exercise regularly to avoid the dangers of a sedentary lifestyle.

ANSWERS

Lesson 2 Assessment

1. Students should describe one of the following: other people, con-taminated water or food, or other organisms (vectors).

2. Sample answer: Emerging diseases can quickly spread across national borders. Therefore, it is important to have an international organiza-tion that can help nations work together to control these diseases.

3. Answers will vary. 4. Sample answer: It is unlikely that

modern medicine will eliminate all biological hazards from Earth because pathogens are always evolving and can evolve resistance to our defenses.