Our Small World

People (and Diseases) on the Move

More people are going more places than ever before. All that movement has a huge health impact. As people move, diseases travel farther and faster than in the past.

The United Nations defines refugees as “people who are outside their country and cannot return owing to a well-founded fear of persecution because of their race, religion, nationality, political opinion, or membership in a particular social group.” They also count those “who have fled because of war or civil conflict.”

In 2006, according to the U.N., there were 8.4 million refugees. Two million of them, the largest chunk, came from Afghanistan. They had moved to Pakistan, Iran, Germany, the Netherlands, and the United Kingdom.

At least another seven million people are “internally displaced.” That means they’ve fled their homes, but have remained within the same country. The largest internally displaced populations are in Iraq and Colombia. Learn more from the U.N.

People move. They always have; they always will.

Sometimes natural disasters, oppression, and wars drive people to migrate. Nearly four million Iraqis, for example, fled their homes between 2003 and 2007; half of them left the country. At other times, people venture in search of economic opportunity. Mexicans go to the United States, Turks to Germany, and Indonesians to Malaysia.


The number of international migrants rose dramatically in recent decades. Source: United Nations


Migration can occur within a country as well. After the U.S. Civil War, countless African Americans moved north in search of a better life. In modern China, about 100 million workers have migrated to the economically prosperous provinces along the coasts.

Human movement can have real benefits. People escape desperate situations, find freedom, build new lives. And an increasing number of people travel for business or fun. Half a billion airline passengers cross international boundaries each year. But migration and travel can also raise serious health issues, because microbes and pathogens can hitchhike aboard unwary travelers. Migrants, moreover, often live in crowded, unsanitary conditions where disease is rife. (See Health & You, below, for more information on migrants.)


Diseases have traveled with humans throughout the ages. In the 1300s, traders and travelers carried bubonic plague from Asia to Europe. This deadly and highly infectious disease swept through Europe, where it became known as the black death. After the discovery of America, European explorers and slave traders brought smallpox, measles, and other illnesses to the New World. These diseases tore through the Native American population, whose members lacked an immunity to the Europeans' germs. In some places, they wiped out 80 to 90 percent of the land's original inhabitants.


A 1937 mural in a U.S. government building depicts a tense encounter with Native Americans over land. While weapons and combat received all the attention, most Native Americans died from disease.
Source: US Department of the Interior


That grim fate befell indigenous peoples in other places too. During the 1850s, measles killed a fifth of Hawaii's people. Two decades later, the disease did the same thing in Fiji. Between 1840 and 1860, influenza (Flu), measles, smallpox, and whooping cough (pertussis) finished off 60 percent of the Maori, the native people of New Zealand.

In the late 1800s and early 1900s, fear of disease underlay many Americans' discomfort with the waves of immigrants coming to the U.S. At Ellis Island, the immigration center in New York Harbor, doctors examined thousands of newcomers daily, keeping a sharp eye out for signs of typhus, tuberculosis (TB), and other communicable diseases.


In or about 1910, a doctor examines immigrants at Ellis Island.
Source: National Park Service



Six hundred million people travel by airplane each year. Source: Varifrank

If people have always spread diseases, what's the big deal about globalization? The answer lies in the word more. More people are going more places than ever before. Air travel has erased physical barriers—oceans, mountains, deserts—that once kept diseases isolated longer. People are also moving more quickly. That makes it far more likely a person carrying germs will spread them long before he or she becomes ill and is recognized as a threat to others' health.

Bleak statistics underscore the health impact of increased mobility. Deaths from infectious diseases have doubled in the U.S. since 1980. Most of those dying were migrants. That doesn't surprise health experts, for migrants the world over are at a higher risk of both contracting and passing on infectious diseases. Migrants, for example, are five or six times more likely to have tuberculosis than other people in the same place.


Good news: The number of tuberculosis cases in the U.S. has dropped, but may be leveling off.
Source: Centers for Disease Control and Prevention


Migrants' health problems are often compounded by dire conditions. That likely happens when war, drought, or disaster uproots large numbers of people. They crowd into a new place, straining local resources. Food, water, and medical supplies become scarce, and sanitation rapidly deteriorates.

Makeshift conditions at a refugee camp in Zaire may allow disease to spread easily.
Source: Centers for Disease Control and Prevention

Under these circumstances, diseases like cholera can suddenly erupt and move rapidly through a densely populated area. This is especially true for people living in refugee camps and relocation centers. Back in 1994, for instance, epidemics killed 50,000 Rwandan refugees during their first month in refugee camps.


Few diseases demonstrate the impact of human movement more vividly than HIV/AIDS, which is caused by the HIV virus. The virus has probably existed among primates for hundreds or even thousands of years in pockets of central African jungle. Yet it only became a pandemic in the past few decades.

What happened? Humans probably contracted the virus by butchering or eating infected non-human primates such as chimpanzees and bonobos. Because humans are genetically very similar to these animals, it would not have been a huge leap for the HIV virus to successfully invade a human host. At first, the infected people didn't travel much, so the disease remained fairly localized. That changed after about 1950. Scientists are not entirely sure why, but it bears noting that the second half of the 20th century was a time of increased movement. Improvements in travel allowed more people to visit Africa, and upheavals on the continent created large groups of migrants and refugees.


The number of people infected with HIV, the virus that causes AIDS,
continues to rise.

Source: AVERT


Due at least in part to increased mobility, the HIV virus spread furiously, in Africa and around the world. In 2005, three million people worldwide died of AIDS and another 40 million were living with the HIV infection. That's just one example of what can happen when people move.



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