About 100 members of the Mashco-Piro tribe clad only in loincloths stood across a riverbank from a tiny town in remote Brazil in late 2013.

From what the townspeople could deduce, they were making accusations about the dwindling numbers of wild pigs called peccaries in the area. The pigs were a major part of their diet.

About a year later, the Mashco-Piro returned with spears and killed the villagers’ chickens and dogs and ransacked their homes before fleeing back into the rainforest. 

More than 8,000 people live in the Amazon rainforest and surrounding ecosystems with no contact with the modern, Western cultures that have sprung up around the jungle. 

The tribes have seemingly chosen to keep themselves isolated, surviving by hunting, gathering, and fishing as they have since before Christopher Columbus was in short pants. 

Image source: Domenico Pugliese/Survival International

But the uncontacted tribes face a growing problem — or, rather, a shrinking problem. And it’s creating health issues for them.

As mining, agriculture, and illegal logging have reduced the size of the Amazon by nearly 20 percent in the past 30 years, the barrier between the tribes and the industrialized world is disappearing, according to an Amazon Watch report.

Isolated peoples “are being pushed to the last remnants of intact forest in the headwaters, the most secluded areas,” Francisco Estremadoyro, the director of ProPurús, a Peruvian conservation group, told Science. “They are already in the deepest jungle they can find.”

Contact between the tribes and the villages along the forest’s edge has become more frequent in recent years, with 25 sightings in the Upper Amazon area since 2009, according to a group of articles in the current issue of Science.

“There’s no question that some of these groups see what they consider their last refuge as being encroached upon and taken and invaded,” Jonathan Mazower, a researcher with Survival International, told Healthline.

With their own resources becoming sparser, some tribes have robbed villages at the forest’s edge, Science reports. 

Just last month, a young man was shot and killed with an arrow at the southern edge of Brazil’s Manu National Park.

But however menacing they may appear, the tribespeople are far more vulnerable than the villagers. Not only do they lack guns. They also have no immunity to many of the diseases Westerners carry.

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A New Page in an Old Book

With the recent uptick in contacts, we may be opening a new chapter in a long story that began in the 1500s with the spread of smallpox that decimated the Aztecs and, later, many North American native groups.

The uncontacted tribes generally lack immunity not just to major diseases like smallpox and measles, but also to malaria, influenza, and the common cold. 

“A cold for us is an inconvenience. For them, it can be a tragedy. Influenza can abruptly wipe out whole tribes,” Peruvian anthropologist Beatriz Huertas, Ph.D., told Science. 

Even when there's no single plague-like event, many indigenous people die as a result of contact with Westerners.

“Long-term cold or flu diseases of the respiratory system almost always occur with these very isolated groups and are very often chronic and are very often fatal,” Mazower said. 

In January, three of a group of 100 isolated Awá Indians in the northeastern Amazon made contact with relatives who had begun to interact with Western civilization. The relatives said it was because they no longer had anywhere to flee to escape illegal loggers.

Survival International mounted a major campaign to safeguard their health. But by April, two were seriously ill from tuberculosis.

“Two of the three of them are now critically ill despite the fact that we and local organizations were pleading with the [Brazilian] authorities to put in place a comprehensive healthcare plan for them,” Mazower told Healthline. 

Even before they emerged from the forest, several Awá people had what appeared to be the flu after loggers encroached on their lands. With no resistance from the immune system, some germs can spread when Westerners and tribespeople touch the same object — sometimes even a gift meant to signal good intentions — or potentially as they speak to each other across a distance.

Why Diseases Are so Destructive to Native Groups

It’s easy to understand how a disease like measles for which most Western people are immunized would wreak havoc in an uncontacted tribe. But why would a cold or flu be deadlier?

The first time a baby in Rio de Janeiro is exposed to a cold virus, the infant is likely still nursing. Breast milk lends children their mothers’ immunity while they develop their own. 

With each exposure, a child’s immune system makes itself a little better equipped to fight that type of disease in the future.

People who are first exposed in later life have immune systems that may be calibrated to fight other types of illness, said Aaron Blackwell, Ph.D., an assistant professor of anthropology at the University of California at Santa Barbara, who studies indigenous groups and immunity.

Image source: Survival International/survivalinternational.org

“Sometimes if they’re exposed to something later in life that they never were early on — or not even exposed to anything similar — they may not respond as well to it,” Blackwell said.

Over generations, populations as a whole may become more resistant to the illnesses they regularly face.

Those who aren’t resistant to the diseases die off. 

“When any population comes into contact with something they’ve never been exposed to, some people immediately have more immunity to that than others. And so when it’s first encountered, people die off,” Blackwell said. “The same thing probably happened in the past with Europeans when they first came into contact, but that happened a little while ago.” 

Evolution is at work in immunity as in anything else. 

“There are many thousands of genetic factors that can affect function of the immune system, and it is likely that these are among the more rapidly-evolving parts of the genome since pathogens evolve very quickly,” explained Melissa Emery Thompson, Ph.D., an anthropologist at the University of New Mexico who focuses on ecology and health. 

“So peoples living in one environment for hundreds of generations should have immune systems that are well adapted to that environment,” Thompson added. “This can often mean that the immune system is biased to be good at combating some kinds of infections, but less good at dealing with others.” 

Why don’t Westerners get new and deadly diseases from the tribes? Some conditions, such as malaria and giardia, hit Westerners harder, Blackwell said, but they aren’t contagious.

When it comes to contagious diseases, the dominant Western culture has numbers on its side. 

“They have such a small population size that the number of communicable diseases circulating is pretty small — there’s not a big enough population to maintain it. So just by chance, it’s far less likely that they’re going to have something that’s really going to affect us than that we’ll have something that will affect them,” Blackwell said.

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Pinpricks or Peccaries?

Deciding how best to protect the indigenous groups’ health has stirred up a heated debate.

In an editorial accompanying the Science articles, anthropologists Robert Walker, Ph.D., assistant professor, University of Missouri, and Kim Hill, Ph.D., professor, Arizona State University, argue that contact is inevitable, so the best approach is to regulate it. They say the uncontacted tribespeople should be offered Western healthcare, including vaccinations.

The alternative is “leaving groups isolated, yet still exposed to dangerous and uncontrolled interactions with the outside world,” they write.   

Survival International sees this view as ethnocentric and naïve. Mazower points to the long history of encounters between settlers and native peoples and the lack of situations in which natives have walked away better off than they were before.

“It’s just wishful thinking because it’s never happened,” he said of the kinds of liberal exchanges Walker and Kim describe. “Given that, it’s terribly dangerous to advocate it.” 

But if contact is inevitable, as the flurry of exchanges in what was once deep forest suggests, the only choice may be to try to make this chapter different, according to Blackwell.

“The whole thing about whether it’s better to contact or not comes down to whether you think that you can isolate them,” he said.

The goal of a structured contact wouldn’t be to force native groups “to change the way they’re living,” Blackwell said. “You’re giving them healthcare while they’re developing their immunity.” 

There’s something uncontroversial about the health of the Amazon tribes, however. It’s those peccaries.

Groups that have access to good hunting grounds don’t show up with malnutrition.

“They’re eating things that are a lot better for you than what we’re eating,” Blackwell said. “In that sense often you’ll see pretty good health.”

Uncontacted people often have parasitic infections and suffer more injuries. They generally die younger than Westerners, Blackwell said, but they don’t get diabetes or cancer. 

In fact, they often get sick when they’re shuttled into the closer quarters industrial life often requires. Settling in Western towns means a radical change in diet. And disease spreads more quickly in close quarters, often facilitated by inadequate sanitation.

“The uncontacted Indians in Brazil are on the whole much better off than the masses of Brazilian poor,” Mazower said. “It’s not like they’re in need of being saved.” 

To protect the people, the best thing is to protect their lands, he said. He shared the story of a group called the Zo’é in the northernmost part of Brazil. After an early encounter with missionaries led to outbreaks of flu and malaria, the Brazilian government set up a watch station to limit contacts between Westerners and the Zo’é. The policy is controversial, but there have been no further disease outbreaks.

“There are tribes in Brazil who are isolated and are doing fine,” Mazower said. “It’s always where the territory is secure, that is the essential thing.”

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