Unit 14 · Global Health

When a mosquito bites a person who has malaria, it sucks up blood that holds a tiny living thing called Plasmodium. This one-celled parasite grows inside the mosquito for about one to two weeks. When that mosquito bites someone else, it injects the parasite along with its saliva. Only female mosquitoes of the Anopheles group spread malaria, because only females drink blood.

Inside the new person, the parasite travels first to the liver, where it multiplies. Then it bursts into the blood and invades red blood cells. The cells break open in waves, which causes the fever, chills and sweating that malaria is known for. Severe malaria can damage the brain and other organs, and young children are most at risk.

For a long time people blamed bad air for the disease. The name malaria comes from Italian words meaning bad air. In 1880 the French army doctor Alphonse Laveran saw the parasite in a patient’s blood. In 1897 the British doctor Ronald Ross showed that mosquitoes carry it. Both men later won Nobel Prizes for this work.

Anopheles mosquitoes bite mostly between dusk and dawn, when people are asleep. That fact gives health workers a clear target. An insecticide-treated net hangs over a bed like a small tent. It blocks bites, and the chemical on it kills or weakens mosquitoes that land on it.

Large studies in Africa during the 1990s found that treated nets lowered child deaths in the areas that used them. Since then, well over a billion nets have been handed out, often for free. Another method is indoor residual spraying, where workers spray the inside walls of homes. Mosquitoes that rest on the walls after feeding are killed.

These tools face a problem. In many places mosquitoes have become resistant to common insecticides, so the chemicals work less well. Scientists answer by making nets with two different chemicals and by switching sprays. Nets also wear out and must be replaced every few years. Prevention works only if it keeps going.

In 1969 the Chinese scientist Tu Youyou was asked to search for a new malaria drug. Older drugs such as chloroquine were failing because the parasite had become resistant. Her team read through old Chinese medical books. They tested hundreds of plant extracts. One plant, sweet wormwood, called qinghao in Chinese, looked promising.

At first the extract worked poorly. Tu noticed that a text by Ge Hong, written about 1,600 years earlier, said to soak the plant in water, with no boiling. Her team switched to a low-heat method, and the extract became powerful. They isolated the active substance, artemisinin, in the early 1970s. Tu Youyou shared the Nobel Prize in 2015.

Today doctors treat malaria with artemisinin-based combination therapy, which pairs artemisinin with a second drug. Using two drugs makes resistance slower to develop. In 2021 the World Health Organization recommended the first malaria vaccine, called RTS,S, for young children in areas with high malaria. A second vaccine, R21, followed in 2023. Neither is perfect, but together with nets they save lives.

In 1882 the German doctor Robert Koch announced that he had found the germ behind tuberculosis, or TB. It is a bacterium now called Mycobacterium tuberculosis. At that time TB was one of the leading causes of death in Europe and the United States. People called it consumption because it seemed to waste the body away.

TB usually attacks the lungs. When a person with active TB in the lungs coughs, tiny droplets carry the bacteria into the air. Many people who breathe them in never become sick; the germ stays quiet in the body. This is called latent TB. Weak nutrition, crowded housing and HIV make it more likely that quiet TB turns into active disease.

Since the 1940s TB has been curable with antibiotics. The usual treatment takes about six months and uses several drugs at once. Stopping too early can let resistant bacteria survive. The World Health Organization reported that about 10.6 million people fell ill with TB in 2022. Most lived in low- and middle-income countries.

In the early 1980s doctors in the United States noticed young adults falling ill with rare infections. Their immune systems had been badly weakened. Scientists identified the cause in 1983: a virus later named HIV, human immunodeficiency virus. Without treatment, HIV slowly destroys immune cells and can lead to AIDS, the most serious stage of the infection.

In 1996 researchers showed that combining three drugs could hold the virus down for years. This is antiretroviral therapy, or ART. A person taking ART every day can live a nearly normal lifespan. When the virus in the blood falls too low to measure, it is not passed on through sex. Health agencies sum this up as undetectable equals untransmittable.

At first ART cost thousands of dollars a year, far out of reach in poor countries. Cheaper generic drugs, and programs such as the Global Fund and the United States program PEPFAR, started in 2003, changed that. UNAIDS reported that by 2022 about 29.8 million of the roughly 39 million people with HIV were on treatment.

In 1854 cholera struck the Soho district of London. The doctor John Snow marked each death on a map. The deaths clustered around a water pump on Broad Street. Snow persuaded local officials to remove the pump handle. He argued that cholera spread through dirty water, not bad air. Most experts at the time did not agree with him yet.

We now know cholera is caused by a bacterium carried in water or food tainted with human waste. It causes severe watery diarrhea, and a person can lose dangerous amounts of fluid within hours. The best protection is sanitation: safe toilets, sewers and treated drinking water. Chicago took a famous step in 1900, when engineers reversed the Chicago River so sewage flowed away from Lake Michigan, the city’s water supply.

Treatment can be simple. Oral rehydration solution is clean water mixed with the right amounts of salt and sugar. The sugar helps the gut absorb the salt and water. Many doctors call it one of the most important medical advances of the twentieth century. Cholera outbreaks still happen where war, floods or poverty damage water systems.

Measles is caused by a virus that spreads through the air when an infected person coughs or sneezes. The virus can hang in the air of a room for up to two hours. It causes a high fever and a rash, and it can lead to pneumonia, brain swelling and death, especially in young children and people who are poorly nourished.

A measles vaccine was licensed in the United States in 1963. Today most children receive it as part of the MMR shot, which also protects against mumps and rubella. The CDC reports that two doses are about 97 percent effective at preventing measles. In 2000 the United States declared measles eliminated, meaning it no longer spread year-round inside the country.

When enough people in a community are protected, the virus cannot find new people to infect. This is called herd immunity. It also shields babies who are too young for the shot. Because measles spreads so easily, about 95 percent of people need to be immune. When vaccination rates drop, outbreaks return, as happened in several U.S. states in 2019.

Some diseases get little attention in wealthy countries because they rarely appear there. The World Health Organization groups about twenty of them as neglected tropical diseases. They include river blindness, sleeping sickness, schistosomiasis and intestinal worms. Together they affect more than one billion people, mostly in poor, rural areas with little clean water.

These diseases often do not kill quickly. Instead they cause blindness, pain, tiredness and disability that can keep children out of school and adults out of work. Some can be treated with cheap pills given to whole communities once or twice a year. This approach is called mass drug administration. Drug companies have donated billions of doses.

Guinea worm disease shows what steady work can do. People catch it by drinking water that holds tiny water fleas carrying the worm’s larvae. There is no vaccine or medicine for it. Instead, villages filter their water and keep people with emerging worms out of ponds. The Carter Center reported about 3.5 million cases in 1986 and only 14 human cases in 2023.

In the early 1950s summer brought fear to American families. Polio, a virus that can paralyze, closed swimming pools and filled hospital wards. In 1955 a vaccine made by Jonas Salk was declared safe and effective. A few years later Albert Sabin developed an oral vaccine given as drops, which was easier to use in large campaigns.

In 1988 the World Health Assembly launched the Global Polio Eradication Initiative. At that time polio paralyzed about 350,000 children a year in more than 125 countries. Health workers went village by village, even into war zones, giving drops to every child under five. Cases fell by more than 99 percent.

Eradication means wiping a disease out everywhere, for good. Only one human disease, smallpox, has been eradicated, confirmed in 1980. Wild polio still spreads in parts of Pakistan and Afghanistan. Conflict, distrust and hard-to-reach communities are the main obstacles. Rich countries stay at risk until polio is gone everywhere, because a traveler can carry it across borders.

After World War II, nations created the World Health Organization, or WHO, in 1948. It is a United Nations agency based in Geneva, Switzerland. The WHO does not run hospitals in most countries. Instead it gathers data, writes guidelines, tracks outbreaks and helps governments plan. It led the campaign that eradicated smallpox.

Newer groups mostly raise and spend money. Gavi, the Vaccine Alliance, began in 2000. It helps low-income countries buy vaccines at lower prices, and it reports helping vaccinate more than a billion children. The Global Fund, created in 2002, pays for programs against AIDS, tuberculosis and malaria. Governments, foundations and companies give to both.

These groups do not always agree, and they face hard choices. Money is limited. Donors may prefer one disease over another. Some critics say global programs should do more to build local health systems instead of fighting one disease at a time. Supporters answer that focused programs show clear results. Both sides want the same goal: fewer people dying of preventable causes.

Malaria once spread in parts of the United States, including along rivers in Illinois. It faded in the twentieth century as swamps were drained, homes got screens and people could afford doctors. The mosquitoes that can carry it still live in the country. What changed was mostly housing, money and health care, not the insects.

Geography matters too. Anopheles mosquitoes need warm weather and standing water, so malaria is heaviest in tropical regions. Cholera follows broken water systems. TB spreads in crowded rooms. But geography alone does not decide who gets sick. Poverty often decides whether a family has screens, clean water, enough food and a clinic nearby.

Public health experts call these conditions the social determinants of health. They include income, schooling, housing, clean water and safe work. A child born in a wealthy country today can expect to live many years longer than a child born in the poorest countries. Closing that gap takes medicine, but also roads, schools, clean water and fair economies.

A chronic disease lasts a long time and usually develops slowly. Heart disease, stroke, cancer, diabetes and long-term lung disease are the main examples. The World Health Organization reports that these noncommunicable diseases cause about 41 million deaths a year. That is roughly three out of every four deaths worldwide.

The most common kind of heart disease starts when fatty deposits called plaque build up inside the arteries that feed the heart. The arteries narrow and stiffen. If a clot forms on the plaque and blocks blood flow, part of the heart muscle is starved of oxygen. That is a heart attack. It often causes chest pain or pressure, shortness of breath and sweating.

A stroke is the same kind of problem in the brain. Most strokes happen when a clot blocks an artery to the brain; some happen when a blood vessel bursts. Brain cells begin to die within minutes. Quick care matters, so health groups teach the signs: a drooping face, a weak arm, and slurred speech mean call emergency services right away.

Your body replaces old cells with new ones all the time. Each cell follows instructions in its DNA about when to divide and when to stop. Sometimes changes in the DNA, called mutations, break those instructions. A cell may keep dividing when it should not. Over time it can form a lump called a tumor.

Cancer is not one disease but more than a hundred. Lung, breast, colon and prostate cancer are among the most common worldwide. Some tumors are benign, meaning they do not spread. Cancer is the name for tumors that invade nearby tissue and can travel through the body, which doctors call metastasis.

Some mutations come from chance as cells copy their DNA. Others come from outside causes. Tobacco smoke is the single largest preventable cause of cancer. Too much sun raises the risk of skin cancer. Some infections play a role too; the HPV vaccine protects against most cervical cancers. Treatments include surgery, radiation and medicines, and many cancers found early can be treated successfully.

When you eat, your body breaks much of your food into a sugar called glucose. It travels in the blood to feed your cells. A hormone called insulin, made by the pancreas, acts like a key that lets glucose into the cells. Diabetes means this system is not working, so sugar builds up in the blood.

In type 1 diabetes, the immune system destroys the cells that make insulin. It often begins in childhood, and people need insulin every day. Insulin was first used to treat patients in 1922 in Toronto, after work by Frederick Banting, Charles Best and others. Before then, type 1 diabetes was nearly always fatal.

Type 2 diabetes makes up about nine out of ten cases. The body still makes insulin but does not respond to it well. Family history plays a part, but so do weight, diet and activity. Large studies found that regular activity and modest weight loss can delay or prevent it in many at-risk adults. Over time, high blood sugar can harm the eyes, kidneys, nerves and heart.

In the 1950s, researchers in Britain and the United States compared people with lung cancer to people without it. Smokers turned up far more often among the patients. In 1964 the U.S. Surgeon General issued a report concluding that cigarette smoking causes lung cancer in men. It was a turning point in public health.

A risk factor is anything that raises the chance of getting a disease. Tobacco is a risk factor for heart disease, stroke, many cancers and lung disease. The World Health Organization estimates that tobacco causes more than 8 million deaths a year, including about 1.3 million people who do not smoke but breathe secondhand smoke. Nicotine, the chemical in tobacco, is highly addictive.

Smoking rates in the United States have fallen by more than half since the 1960s. Taxes, smoke-free laws, warning labels and support to quit all helped. Vaping devices also deliver nicotine, and health agencies advise young people not to use them. The good news is clear: the body starts to recover soon after a person quits, and help is available from doctors and quit lines.

Each time your heart beats, it pushes blood against the walls of your arteries. Blood pressure is the force of that push. A nurse measures it with a cuff and writes two numbers, such as 118 over 76. The top number is the pressure during a heartbeat; the bottom is the pressure between beats.

When pressure stays too high for a long time, it strains the heart and damages arteries. This is called hypertension. It is a leading risk factor for heart attack and stroke. Most people with hypertension feel perfectly fine, which is why doctors call it a silent condition. The only way to know is to measure it.

The World Health Organization reported in 2023 that about 1.3 billion adults aged 30 to 79 have hypertension, and nearly half do not know it. Less salt, more activity, less alcohol and not smoking all help. Many people also need daily medicine. A research program in the 1940s, the Framingham Heart Study in Massachusetts, helped show how strongly blood pressure predicts heart disease.

Nutrition scientists agree on a few broad patterns. Diets rich in vegetables, fruits, whole grains, beans and nuts are linked to lower rates of heart disease, type 2 diabetes and some cancers. Diets high in sugary drinks, processed meat and salty packaged foods are linked to higher rates. Scientists still debate many details, such as exactly how much fat or which kinds are best.

Much of the salt people eat comes not from the salt shaker but from bread, canned soups, chips and restaurant food. Too much salt raises blood pressure in many people. Ultra-processed foods, made mostly from refined ingredients and additives, are easy to overeat and are a growing share of diets in many countries.

Moving your body matters as much as food. Physical activity strengthens the heart, helps control blood sugar and blood pressure, and improves mood and sleep. The World Health Organization recommends that children and teens get an average of at least 60 minutes of moderate to vigorous activity a day. Walking, dancing, biking, sports and active chores all count.

The Okinawa Centenarian Study, begun by Makoto Suzuki in 1975, followed hundreds of people aged one hundred or older. Researchers found that older Okinawans had eaten a traditional diet based on sweet potatoes, vegetables, soy foods and some fish. Calories were modest. Many practiced hara hachi bu, stopping before they felt completely full.

The diet was only part of the picture. Older Okinawans kept working in gardens and fields into old age. Many belonged to a moai, a group of friends who met regularly for life and supported one another. Researchers think purpose, friendship and daily movement may matter along with food, though separating each piece is hard.

Scientists are careful about what one place can prove. People who live long may share genes as well as habits. Some researchers have questioned how accurate very old birth records were in several long-lived regions. The strongest clue is what happened next: as younger Okinawans ate more fast food and moved less, their health advantage shrank. That change points to lifestyle, not genes alone.

In the 1950s the American scientist Ancel Keys noticed that heart attacks seemed rare in parts of southern Italy and on the Greek island of Crete. In 1958 he began the Seven Countries Study, comparing men in the United States, Finland, the Netherlands, Italy, Greece, Yugoslavia and Japan. Men in Crete and Japan had some of the lowest rates of heart disease.

The Mediterranean diet, as later studies described it, features vegetables, fruit, beans, whole grains, nuts, fish and olive oil, with little red meat or sweets. Meals are often shared slowly with family. In 2010 UNESCO listed the Mediterranean diet as part of the cultural heritage of humanity, honoring its traditions of farming, cooking and eating together.

A large Spanish trial called PREDIMED, published in 2013, found fewer heart attacks and strokes among people told to eat this way with extra olive oil or nuts. In 2018 the authors withdrew and reissued the paper after finding problems in how some people were assigned to groups. The new analysis found similar results, but with more caution. Many experts still see this pattern as healthy, while debating how much each part matters. This is how evidence grows and gets tested.

Imagine two students walking home from school. One passes a grocery store with fresh fruit and a park with a basketball court. The other passes three fast-food restaurants and a gas station, with no store selling fresh produce for a mile. Both students want to eat well, but their choices are not the same.

Researchers call these surroundings a food environment: the stores, restaurants, prices and advertising around a person. The U.S. Department of Agriculture has studied areas where many people live far from a supermarket and have low incomes. These areas are sometimes called food deserts. People living there often rely on small stores with more packaged food.

Food environments can be changed. Some cities offer incentives for grocery stores to open in underserved neighborhoods. Schools can serve healthier lunches and put water fountains in easy reach. Farmers markets can accept food assistance benefits. Researchers still debate which changes help most, since a new store does not always change what people buy. But the idea is clear: access shapes habits.

In the 1940s the Greek-American doctor George Papanicolaou showed that looking at cells from the cervix under a microscope could reveal early signs of cancer. His test, the Pap test, became routine. Deaths from cervical cancer in the United States fell sharply in the following decades, in large part because early changes were found and treated.

Screening means testing people who feel well to find a disease early. Blood pressure checks, blood sugar tests, mammograms for breast cancer and colonoscopies for colon cancer are examples. Finding a cancer while it is small often makes treatment simpler and more successful.

Screening is not free of problems. A false positive is a result that suggests disease when none is there, which can bring worry and more tests. Some screening finds slow cancers that would never have caused harm. That is why expert groups weigh benefits and harms and sometimes disagree about the best age to start a test. Patients decide with their doctors.

In 1972 the region of North Karelia in Finland had one of the highest rates of heart disease deaths in the world. Local leaders and health workers launched a community project. They worked with farmers, food companies, schools and shops to cut salt and saturated fat, promote vegetables and help people quit smoking. Over the following decades, heart disease deaths among working-age men there fell dramatically.

This is prevention: stopping disease before it starts. Treatment helps people who are already sick, with medicines, surgery or care. Both matter. A person having a heart attack needs a hospital now. But a community that lowers everyone’s blood pressure a little may prevent many heart attacks from ever happening.

The British epidemiologist Geoffrey Rose called this the prevention paradox. A small change across a whole population can prevent many cases, yet each single person may notice little benefit. That can make prevention hard to value, because the people it helps never know they were spared. Societies debate how much to spend on each side and how far governments should go in shaping choices like food and tobacco.

In Japan, most elementary and junior high schools serve lunch planned with trained nutritionists. Students often serve the food to classmates and eat together in the classroom. The meals follow washoku, the traditional Japanese way of eating, which UNESCO recognized as cultural heritage in 2013. Eating becomes a shared lesson, not just a break.

Culture is the shared beliefs, habits and traditions of a group. It shapes which foods feel like home, when families eat, whether people walk or drive, and how celebrations are marked. Traditional medical systems carry cultural ideas about food too. Ayurveda, for example, teaches choosing foods to keep the body’s doshas in balance, an idea from that tradition rather than a measured fact.

Health programs work better when they respect culture. A program that tells a family to give up its favorite dishes often fails. A program that helps cook those dishes with less salt, or that builds on a tradition of walking to market, has a better chance. Health workers who come from the community, like the health worker in Kenya, often know what will fit.