Henrietta Lacks’ cancer cells, called HeLa, are used around the world for medical experiments.
Credit: © Pictorial Press Ltd, Alamy Images

February is Black History Month, an annual observance of the achievements and culture of Black Americans. This month, Behind the Headlines will feature Black pioneers in a variety of areas.

A mother and a medical marvel with a lasting legacy, Henrietta Lacks has saved nearly 10 million lives. Lacks was an African American woman born in Roanoke, Virginia, on August 1, 1920. Lacks unknowingly became a donor of a line of cells widely used in medical research. Those cells, known as HeLa cells, became one of the most important advances in medical science. HeLa stands for Henrietta Lacks. Lacks only lived 31 years, but her cells are still alive today.

Lacks was born Loretta Pleasant. She later changed her name to Henrietta and married David Lacks in 1941. The couple moved to Baltimore, Maryland, in the 1940’s. In 1951, she was diagnosed with cervical cancer at the Johns Hopkins Hospital. She died on October 4 of that year, leaving behind her five children. Before her death, doctors removed a sample of cancer cells during a medical examination. The sample was taken without her knowledge.

Scientists at Johns Hopkins University used the sample to establish the HeLa cell culture. A cell culture is a population of cells grown under controlled conditions for research. The usefulness of cell cultures is often limited because the cells die after a certain number of divisions. However, the HeLa cells divided indefinitely without dying.

HeLa cells grow faster than other cell cultures. They survive shipment by mail, enabling them to be sent to laboratories around the world. The unique qualities of HeLa cells led to many scientific discoveries and a greater understanding of biological processes. One of the first uses of HeLa cells was to test the safety and effectiveness of a vaccine for the disease polio. HeLa cells have also contributed to treatments for Parkinson’s, HIV, and AIDS, as well as vaccines for the flu, HPV, and COVID-19. Her cells have been used in nearly 75,000 studies.

The World Health Organization honored Henrietta Lacks in 2021. The city of Roanoke, Virginia, is replacing a statue of confederate general Robert E. Lee with a bronze statue of Lacks. Nearly 72 years after her death, Lacks will be memorialized in her hometown for years to come. Author Rebecca Skloot wrote about Henrietta’s life and her medical contribution in The Immortal Life of Henrietta Lacks released in 2010. The story was adapted into a movie in 2017 starring Oprah Winfrey.

HeLa cells were also used to produce the first cellular clones. Cellular clones are a group of cells descended from a single cell. They are genetically identical, enabling scientists to study entire populations of cells with a particular genetic trait.

HeLa cells remain an essential tool in laboratories throughout the world. They have been used to develop drugs and other therapies worth billions of dollars. However, Henrietta Lacks and her family received no compensation for the use of her cells. In medical ethics, her case is often cited as a classic example of failure to obtain informed consent from a tissue donor. Informed consent means that participants fully understand and accept the known risks and possible benefits of a medical procedure. Today, researchers regularly obtain consent from patients before taking tissue samples.

In 2013, the United States National Institutes of Health (NIH), a government agency that conducts and supports a broad range of biomedical research, made a historic agreement with the surviving family of Henrietta Lacks. NIH researchers must now obtain permission from a special review panel before they can view and use detailed genetic information of HeLa cells. Members of the Lacks family are included on the review panel. NIH also requested that researchers studying HeLa cells include an acknowledgment to the Lacks family when the research is published.

AIDS viruses reproduce in CD4 cells and circulate in the blood. In this electron micrograph of a white blood cell, AIDS viruses can be seen as the small white dots covering the cell’s surface.
Credit: Centers for Disease Control and Prevention

Today, December 1, 2022, is World AIDS Day. AIDS is the final, life-threatening stages of infection with the human immunodeficiency virus (HIV). HIV damages the immune system, the human body’s most important defense against disease. AIDS stands for acquired immunodeficiency syndrome or acquired immune deficiency syndrome. On this day, we honor over 40 million people who have lost their lives to AIDS and look ahead to ending the AIDS pandemic through research, healthcare, and community support. The World Health Organization reported that 38.4 million people were living with HIV across the globe at the end of 2021.

AIDS is a relatively new life-threatening disease. HIV is spread through sexual intercourse with an infected person or exposure to blood from an infected person, many times through shared needles used to inject drugs. At first, it mainly affected young adults. In the public imagination, the disease soon became associated with risky sexual behavior and with drug abuse. For all these reasons, efforts to address AIDS or to prevent the spread of HIV have at times faced unique social challenges. An infected pregnant woman can transmit HIV to her unborn child before and during the delivery, even if the woman shows no symptoms. An HIV-infected mother may also pass HIV to her baby through breast-feeding.

Since 1986, the international health community has worked to coordinate the global fight against HIV and AIDS. The World Health Organization’s Global AIDS Programme formed the Joint United Nations Programme on HIV/AIDS (UNAIDS) in 1996. Since that time, UNAIDS has worked with other international partners to coordinate the global fight against HIV and AIDS. UNAIDS reported recently that one obstacle to ending AIDS around the world is gender inequality. Many girls and women live with HIV and AIDS without treatment and education to prevent infection. They report that in countries where girls do not receive an education, the rates of HIV infection are higher. UNAIDS also stated that in countries where same-sex relationships are criminalized the probability of infection is increased.

Many individuals and organizations have worked to increase public awareness of AIDS. The most active organizations include community-based groups and the American Red Cross. They hope that greater awareness will generate more compassion and support for people living with AIDS. They also hope to ensure adequate funding for HIV prevention, treatment, and research. One prominent project bringing attention to the crisis is the AIDS Memorial Quilt. Begun by the NAMES Project Foundation in 1987, the quilt consists of thousands of individually designed panels. The panels memorialize people who died of AIDS. The quilt has been displayed throughout the world.

Poor understanding of HIV has at times stoked public fears, leading many people with the virus to suffer unjustly. Some of the infected have lost or been denied jobs or housing. Others have been denied medical care and health insurance. Many children with AIDS were initially barred from attending school or playing on sports teams. To prevent discrimination, people with HIV and AIDS are often included under laws protecting the rights of people with disabilities. The United States government and some states have also strengthened laws safeguarding the confidentiality of medical records relating to HIV infection and AIDS.

Preventing discrimination against people with HIV is not only just—it also protects public health. When people can live without fear of discrimination, they are more likely to seek counseling and treatment. In many cases, such measures lead to earlier diagnosis and a reduction in risky behavior.

AIDS was first identified as a disease by physicians in California and in New York City, New York, in 1981. Doctors recognized the condition as something new because all the patients were previously healthy, young gay men. They sought medical care because they were suffering from otherwise rare forms of cancer and pneumonia. In 1982, the disease was named AIDS. Scientists soon determined that AIDS occurred when the immune system became damaged. They also learned that the agent that caused the damage was spread through sexual contact, shared drug needles, and infected blood transfusions.

AIDS occurs in every nation. In areas such as Africa south of the Sahara, Southeast Asia, and India, HIV transmission has occurred mostly among heterosexual men and women, particularly young adults and teens. Many developing nations carry enormous burdens of HIV infection. For example, the United Nations reports that in some parts of Africa, the infection rate may reach over 30 percent in some urban areas. The huge number of young adults dying of AIDS in Africa south of the Sahara has decreased overall life expectancy across the continent. A growing number of people have also become infected in countries with increasing drug use, such as Russia, China, and the nations of central Europe.

An electron microscope shows monkeypox virus particles.
Credit: Cynthia S. Goldsmith and Russell Regnery, CDC

On May 13, 2022, the World Health Organization was notified of two confirmed cases of monkeypox in the United Kingdom. Not the chickenpox, monkeypox! Since then, cases have been detected in Canada, Italy, Portugal, Spain, Sweden, and the United States. Many people are now asking: what is monkeypox and how bad is it?

Monkeypox is a viral disease that affects animals and, in rare cases, human beings. Scientists first isolated and identified the monkeypox virus from laboratory monkeys in 1958. They obtained it from monkeys that had an unusual rash of skin pustules (small bumps filled with fluid). Historically, such pustules were called pox, leading to the name monkeypox. Other animals, including rats, squirrels, and mice, can also carry monkeypox.

People that eat or get bitten by infected animals can catch monkeypox, but the virus does not spread easily from person to person. The disease is uncommon in human beings. The first human case of monkeypox was not recorded until 1970.

Monkeypox occurs naturally among wild animal populations of central and western Africa. Since the 1970’s, it has caused occasional outbreaks of illness among people in the region. In 2003, 71 people in Illinois, Indiana, Kansas, Missouri, Ohio, and Wisconsin became ill with confirmed or suspected cases of monkeypox. They caught the disease after handling prairie dogs that were purchased at a pet shop in Illinois. Prairie dogs do not naturally carry the monkeypox virus. The animals became infected at the pet shop, where they were housed with a rodent called a Gambian giant rat that carried the virus. An animal dealer had imported the rat from Africa to sell it as a pet.

Several people were hospitalized in the 2003 outbreak, but there were no deaths. Physicians and veterinarians quickly quarantined (isolated) people and animals that might have been exposed to the virus. This action was designed to prevent the disease from spreading to other people, pets, or wild animals. Following the outbreak, the United States Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) banned the importation of rodents from Africa. They also banned the transport and sale of prairie dogs and African rodents within the United States.

Symptoms of the disease develop about two weeks after a person is exposed to the monkeypox virus. Symptoms include fever, headache, muscle pain, backache, and swelling of lymph nodes. Following the fever, a rash appears on the face and other parts of the body. The rash develops into fluid-filled pustules, which dry up and fall off. The illness lasts from two to four weeks. In Africa, from 1 percent to 10 percent of people infected with monkeypox die from the disease.

Physicians suspect monkeypox if a person shows the symptoms and has had contact with an infected person or animal. Laboratory tests are used to detect the monkeypox virus in samples from blood, pustules, or scabs of patients.

People can prevent infection by not handling wild animals that may carry the virus. The monkeypox virus is related to the virus that causes smallpox. Smallpox vaccine can protect against monkeypox when it is given before a person is exposed to the virus. Smallpox vaccination given after exposure to monkeypox may help prevent the disease or make it less severe. However, because the disease is uncommon, health officials do not recommend widespread smallpox vaccination to protect people from monkeypox.

February 24, 2020

Last week, on February 19, the Wuhan coronavirus epidemic claimed its 2,000th victim. First recognized in human beings in the Chinese city of Wuhan in December 2019, the coronavirus has since spread steadily and touched nearly all parts of the world. Wuhan coronavirus is an informal name for a respiratory disease named Coronavirus Disease 2019 (COVID-19). Coronaviruses are one of many virus types that cause the common cold and other diseases of the upper respiratory system. The COVID-19 is a pneumonia-like disease. Its symptoms include breathing difficulties, coughing, and fever. It is a contagious disease, and the symptoms can be fatal in a small percentage of cases.

This illustration of Coronavirus Disease 2019 (COVID-19) shows the spikes on the outer surface of the virus that appear as a corona, giving the virus its name. Credit: Centers for Disease Control and Prevention (CDC)

On Jan. 30, 2020, when the disease had caused 170 deaths in some 8,000 confirmed cases, the World Health Organization (WHO) declared the virus outbreak to be a public health emergency of international concern. The WHO recommended urgent containment measures as the number of cases and deaths continued to climb. By mid-February, more than 40,000 cases of the virus had been confirmed. The disease was given the temporary name 2019-nCoV, for novel (new) coronavirus of 2019. It was later officially named COVID-19. The virus that causes the disease was named SARS-CoV-2.

February 3, 2016

A large number of diseases, including the Zika virus, are spread by mosquitoes. Credit: © Dmitry Knorre, Dreamstime

The World Health Organization (WHO) declared an international public health emergency in response to a frightening outbreak of Zika virus across South America, Central America, and the Caribbean. WHO reserves such emergency declarations only for extraordinary events that are “serious, unusual or unexpected.” WHO has only declared such an emergency on three other occasions. The first occurred in 2009, when a pandemic of H1N1 influenza, called “swine flu” spread across the globe. In 2014, WHO deemed the outbreak of Ebola virus in Africa and a resurgence of poliomyelitis (polio) in Syria international public health emergencies. This week’s declaration is an urgent call for action to focus international attention and resources on fighting the widespread outbreak of Zika virus that is strongly suspected of causing thousands of cases of severe birth defects in Brazil and elsewhere.

Since November 2015, Brazilian health authorities have observed a dramatic increase in babies born with microcephaly. With this condition, a child is born with a smaller-than-normal sized head, often with severely impaired brain development. Several of the babies with this condition and their mothers tested positive for exposure to the Zika virus, strongly indicating a link between the virus and the birth defect. WHO officials have since found that the Zika virus was spreading explosively through 24 countries and territories in Central and South America and the Caribbean. They believe as many as 4 million people may become infected in the months since November 2015.

The Zika virus was first discovered in the 1950’s in Africa, where it occurs naturally. It is usually spread to people through the bite of a mosquito, Aedes aegypti, common throughout tropical regions of the world. It had not been detected in South America until 2015. Symptoms of Zika virus disease include fever, rash, joint pain, and conjunctivitis (eye inflammation). For adults and children, the illness is usually mild, with symptoms lasting up to a week. Severe Zika virus infections, requiring hospitalization or causing death, are uncommon. Doctors do not yet understand how the Zika virus may cause microcephaly and why this serious condition has not been associated with the virus in previous outbreaks.

The emergency declaration by WHO will facilitate a coordinated response by various international health agencies including the United States Centers for Disease Control and Prevention. This will greatly help improve methods to detect the Zika virus, implement mosquito control measures to prevent the spread of the virus, and speed work on a possible vaccine in hopes of controlling the disease. WHO officials did not recommend restrictions on travel or trade to countries where the Zika virus is detected. However, travelers to affected regions are advised to practice basic mosquito-control measures. For example, people in affected areas should limit skin exposure by wearing long sleeves and pants, and wear mosquito repellant as necessary during the day, when the mosquitoes that transmit Zika virus are known to bite. Brazil is due to host the Olympic Games in Rio de Janeiro in August 2016, which will bring a great many visitors to the country, increasing the number of people who could become infected with the Zika virus.

Other World Book articles:

• Travelers Warned of Zika Virus (Jan. 19, 2016) – A Behind the Headlines article

August 1, 2014

Efforts to control the Ebola outbreak in West Africa are not keeping up with the speed with which the deadly virus is spreading, World Health Organization (WHO) General-Director Margaret Chan declared today. Speaking at a summit of regional leaders, Dr. Chan warned that failure to contain the deadly disease could be “catastrophic in terms of lost lives but also severe socioeconomic disruption and a high risk of spread to other countries. . . . Cases are occurring in rural areas which are difficult to access, but also in densely populated capital cities.” However, Chan does believe that the current outbreak can be stopped, and she announced that WHO is launching a $100-million Ebola response plan in the worst affected countries–Guinea, Liberia, and Sierra Leone.

Yesterday, Tom Frieden, the director of the U.S. Centers for Disease Control and Prevention (CDC),   announced that the agency is sending 50 additional personnel over the next 30 days to help the 12 staff members already on the ground in West Africa. “The bottom line is that Ebola is worsening in West Africa,” he said. The announcement came after the CDC raised its travel health alert to Level 3, the highest level, for Guinea, Liberia, and Sierra Leone. The CDC warned people to avoid nonessential travel to those countries.

According to the World Health Organization, the latest outbreak of Ebola has left 729 people dead, including top physicians in Liberia and Sierra Leone. The outbreak has also sickened two Americans–a doctor and a medical aid–who are being flown to CDC medical facilities in Atlanta. There is no vaccine to prevent the illness, and no specific treatment for it beyond attempting to nurse people through the worst of the fevers, bleeding, and other symptoms. The only way to stop an outbreak is to isolate each infected patient and trace all of his or her contacts and isolate them in turn.

The current outbreak of Ebola fever began in southern Guinea and quickly spread to Liberia and Sierra Leone. (World Book map; map data © MapQuest.com, Inc.)

Lansana Gberie, a prominent scholar from Sierra Leone, has condemned his government’s response to the outbreak: “The whole thing has been very incompetently handled. If the government had quarantined this area [in remote northwestern Sierra Leone] they could have contained it. Instead they opened a treatment center in Kenema, a major population center.”

Two of the three affected countries have begun to respond to the crisis. Sierra Leone has declared a public health emergency, and the president, Ernest Bai Koroma, has ordered security forces deployed to support health professionals. “All epicenters of the disease will be quarantined,” said Koroma, along with “localities and homes where the disease is identified and searched for infected people.” Public meetings are restricted, and he ordered top officials to cancel all but essential overseas travel.

In Liberia, the government has closed most border crossings and ordered the deployment of security forces to combat the outbreak. Public gatherings have been banned and schools closed. Nonessential government workers have been put on compulsory leave for 30 days.

Additional World Book articles:

• Africa 1995 (a Back in Time article)
• Africa 1996 (a Back in Time article)
• Uganda 2012 (a Back in Time article)
• The Origin of New Diseases (a special report)

March 7, 2014

Warmer temperatures, associated with global warming, are causing malaria to become more common at higher altitudes, according to a report in the latest issue of the journal Science. A study of malaria in the highlands of Africa and South America by an international team of scientists found that generally higher temperatures in the future may well lead to millions of additional people exposed to the mosquito-borne disease.

Malaria, a disease common in tropical and subtropical regions, is caused by infection with parasites called Plasmodia. The parasites are one-celled organisms called protozoans. They are transmitted to human beings through the bite of the female Anopheles mosquito.

“The impact in terms of increasing the risk of exposure to disease is very large,” stated the lead author of the study, Mercedes Pascual of the University of Michigan. Pascual noted that in the past, higher altitudes provided  protection against this devastating disease because both the malaria parasite and the mosquito that carries it do not thrive in cooler air.

Malaria parasites appear in pink and blue in a false-color image. (c) CNRI/SPL from Photo Researchers

Pascual and her team studied densely populated areas in the highlands of Colombia and Ethiopia, where scientists have kept detailed records of both temperature and malaria cases from the 1990’s to 2005. The team found that malaria shifted higher into the mountains in warmer years and stayed at lower elevations in cooler years. “We have estimated that, based on the distribution of malaria with altitude, a 1-Celsius-degree (1.8-Fahrenheit-degree) rise in temperature could lead to an additional 3 million cases in people under 15 years old,” stated Pascual. Climatologists predict that Earth’s surface temperature could rise by as much as 1 Celsius degree by 2030.

The World Health Organization estimates that there were about 207 million cases of malaria in 2012 leading to approximately 627,000 deaths. Children living in Africa are particularly hard hit by the disease.

Additional World Book articles:

• Charles Louis Alphonse Laveran
• Sir Ronald Ross
• Blood Feeders: Real-Life Vampires (a Special Report)
• The Timeless Scourge of Malaria (a Special Report)

October 25, 2013

At least 22 people—primarily babies and toddlers—are now believed to have contracted polio in Syria, the World Health Organization (WHO) reported this week. The polio outbreak is the first in Syria in at least 14 years. Before the civil war in Syria began in 2011, an estimated 95 percent of Syrian children were vaccinated against polio. The war, however, has crippled public health systems; fully half of the country’s hospitals have been destroyed or are so severely damaged as to be inoperable. According to UNICEF (United Nations International Children’s Emergency Fund) estimates, at least a half a million Syrian children, all under age 5, have not been immunized and are at risk of polio.

Some 5 million Syrians have been displaced by the civil war and generally live in overcrowded, unsanitary conditions. Desperately short of food and medicine, many are living hand-to-mouth in parks, vacant buildings, or in cramped quarters with relatives. At least 2 million Syrian have left the country, and people continue to flood across borders in an uncontrolled manner. UNICEF spokesperson Simon Ingram points out that this exodus “increases the possibilities and means by which the [polio] virus can spread.” WHO has also reported increases in cases of hepatitis A, measles, and typhoid in refugee camps in Egypt, Jordan, and Turkey.

An infant receives a polio vaccination as part of a UNICEF immunization program. Polio remains endemic in Afghanistan, Nigeria, and Pakistan. Conditions in Syria recently led to an outbreak of polio there, as well. (AP/Wide World)

In 1988, WHO launched an immunization campaign that has largely eradicated polio in developed countries. However, the disease remains endemic in Afghanistan, Nigeria, and Pakistan. A Taliban ban on vaccination in Afghanistan and Pakistan threatens to derail the dramatic progress made toward wiping out polio. The Taliban denounces vaccination as a Western plot to sterilize Muslims.

Additional World Book articles:

• Syria 2011 (a Back in Time article)
• Syria 2012 (a Back in Time article)
• Jordan 2012 Ia Back in Time article)
• Turkey 2012 (a Back in Time article)
• Fighting a Persistent Foe (a special report)
• Syria: The Roots of a Rebellion (a special report)

October 22, 2013

Air pollution in the northeast Chinese city of Harbin was literally off the chart yesterday, forcing the closure of schools, paralyzing traffic, and shutting down the airport. In parts of the city, visibility was near zero. “You can’t see your own fingers in front of you,” declared the city’s official news site.

Coal-burning plants and factories, which are common in China, produce sulfur dioxide, an air pollutant that causes acid rain and produces dangerous particulate matter in the atmosphere (© age fotostock/SuperStock).

The Harbin government reported an air quality index (AQI) score of “above 500″; 500 is the upper limit on scales used by both the Chinese government and the U.S. Environmental Protection Agency (EPA). By comparison, the AQI score in New York City yesterday was 41. The EPA labels any reading between 301 and 500 as “hazardous.” The standards set by the World Health Organization characterizes a score above 500 to be more than 20 times the level of particulate matter in the air deemed safe.

The China News service reported that yesterday’s PM2.5 (particulate matter with a diameter of 2.5 micrometers) measurement in Harbin topped 1,000 micrograms per cubic meter. This surpassed the peak of 900 in Beijing in January in what became known as that city’s “air-pocalypse.” Health experts note that particles at a level of PM2.5 are particularly dangerous because the matter is small enough to penetrate deep into the lungs and enter the bloodstream.

The Harbin weather bureau blamed the pollution on a lack of wind; local farmers burning corn stalks after the harvest; vehicular emissions; and the firing up of the municipal central heating system—coal-burning boilers that provide hot-water heat to the entire city of 3.5 million. China remains heavily dependent on coal. Fully 68.4 percent of China’s energy usage is from coal, much of it high sulfur-content coal. When coal is burned, its sulfur content combines with oxygen to form sulfur dioxides. Sulfur dioxide is a pollutant gas that contributes to the production of acid rain and causes significant health problems, particularly through its role in forming particulates.

Additional World Book articles:

• The Case for Renewables (a special report)
• China 2012 (a Back in Time article)

January 15, 2012

Air pollution in China’s capital, Beijing, has for the past week greatly surpassed levels considered hazardous by the World Health Organization (WHO). According to the Beijing Municipal Environmental Monitoring Center, the density of a kind of particle pollution known as PM2.5 soared to 700 micrograms per cubic meter in many parts of the city on January 12, a level considered extremely dangerous. An unofficial reading from a monitor at the United States embassy in Beijing registered levels of more than 800 micrograms per cubic meter. According to WHO standards, levels above 25 micrograms are considered unsafe. Yesterday, levels dropped to about 350 micrograms on the Beijing government scale, still dangerously high.

According to the U.S. Environmental Protection Agency, particle pollution, also known as particulate matter (PM), is a mixture of microscopic solids and liquid droplets suspended in air. PM includes such acids as nitrates and sulfates, organic chemicals, metals, soil or dust particles, and such allergens as fragments of pollen or mold spores. PM exists in a wide range of sizes. Particle pollution that is less than 2.5 micrometers in diameter–1/30th the diameter of a human hair–is known as PM2.5. Such pollution can penetrate deep into the lungs. Numerous health studies have linked PM to premature death from heart or lung disease, according to the EPA. The Beijing Shijitan Hospital reported a marked increase in the number of patients seeking treatment for asthma, chronic bronchitis, emphysema, and other respiratory illnesses associated with exposure to PM2.5.

Beijing can easily be seen in a satellite image of northeastern China made on January 3, 2013. (NASA)

Extremely heavy pollution obscures Beijing and surrounding areas in a second satellite image, made on January 14, when pollution levels were 15 times greater than the level considered “safe” by the World Health Organization. (NASA)

Fuel combustion–the burning of fossil fuels and biomass–is a major source of PM2.5. Sulfate particles form when sulfur dioxide emitted from electric power and industrial plants reacts with sunlight and water vapor in the air. Nitrate particles form in the same way from nitrogen oxides emitted by electric power plants and automobiles and other forms of combustion.

Rapid industrialization, a reliance on coal for power, and the explosive growth in car ownership has made air pollution a major problem in China. Weather conditions and the burning of coal for heating generally make conditions worse in winter. When coal, a carbon-based mineral, is burned, sulfur and nitrogen oxides are released into the air. In 2010, China was dependent on coal for nearly 80 percent of its energy and electric power output, according to the International Energy Agency.

Additional World Book articles:

• Smog
• Advances in Understanding Asthma (a special report)
• The Case for Renewables (a special report)
• China’s Global Awakening (a special report)