In a terse, one-page announcement last week, Brazil’s Indian affairs department (FUNAI) let it be known that an isolated tribe in the Amazon region had just taken a momentous and potentially tragic step. Emerging from dense rainforest along the Upper Envira River in the state of Acre, Brazil, the group willingly approached a team of Brazilian government scientists on 29 June and made peaceful contact with the outside world.

The event—Brazil’s first official contact with an isolated tribe since 1996—was not entirely unexpected. Since early June, fearful villagers in the region had radioed Brazilian authorities at least twice about a group of some 35 tribal strangers who were raiding their crops and trying to make off with machetes and other tools. Recognizing the potential for trouble, FUNAI dispatched a team of specialists, including medical personnel and Brazilian anthropologist José Carlos Meirelles, an adviser on indigenous matters to the government of Acre.

FUNAI’s swift response is commendable, says anthropologist Kim Hill of Arizona State University, Tempe, who has conducted extensive fieldwork among Amazon rainforest tribes. Since 1987, the agency has maintained a no-contact policy, except in cases where a tribe’s survival was deemed to be in peril. That was probably the case here, Hill notes. “There was a serious threat of violence between two native populations, and the intervention should eliminate that,” he says. But Hill and others remain deeply concerned about the future of the newly contacted tribe as it encounters novel diseases and resource-hungry outsiders. As much as 60% of a newly contacted Nahua population in the Peruvian Amazon died between 1983 and 1985 from influenza, whooping cough, and other diseases caught from loggers, noted Beatriz Huertas Castillo, a private Peruvian scholar, in a 2004 report.

The massive Amazon rainforest holds the world’s largest concentration of isolated tribes—at least 70 in the Brazilian Amazon alone, according to FUNAI. Many, if not most, have had at least fleeting contact with the outside world, particularly during Brazil’s rubber boom in the late 19th and early 20th centuries, when rubber tappers made a practice of rounding up and enslaving indigenous tribespeople. After that, many populations fled to remote Amazon headwaters and cut off all contact with outsiders.

It is not yet clear what prompted the tribe along the Upper Envira River to end its long seclusion. The FUNAI field team has yet to identify the tribe’s language, much less ask for its story, and has now requested the assistance of linguists.

But officials think the tribe most likely migrated from a large area in Peru that includes Murunahua Territorial Reserve and Alto Purús National Park, some 300 kilometers away. Although the land is protected on paper, illegal loggers there have built roads and set up base camps to cut down valuable mahogany. The logging is selective, but the heavy machinery may be frightening off wild game, an important source of food for isolated people.

The cocaine trade is also encroaching on the protected area, according to an online report in GeoJournal in 2011 by geographer David Salisbury of the University of Richmond and Chris Fagan, executive director of the Upper Amazon Conservancy in Jackson, Wyoming. Processors have set up camps to make cocaine paste, and heavily armed traffickers now use the tribes’ traditional migratory trails to reach river tributaries in order to transport the product into Brazil. “On the Purús River, the number of conflicts between uncontacted tribes and both coca workers and loggers has increased in recent years resulting in deaths on both sides,” Salisbury and Fagan wrote.

The newly contacted tribespeople may have been fleeing such conflicts, but Hill says that they may also have scouted out desirable resources such as game in the Upper Envira River area in Brazil. Or, he adds, “they might have discovered that they can raid weaker neighbors and get goodies.”

Either way, the tribe’s decision to move and make contact with the outside world leaves them vulnerable. The top priority now, says anthropologist Robert Walker of the University of Missouri, Columbia, is to prevent disease transmission by quarantining the area, giving access only to individuals screened by medical personnel, and providing food and medical care to the elderly and young, who are at the highest risk of infection. “Vaccinations are a possibility at some point,” Walker says. But he adds that immunizations may frighten tribespeople, causing them to flee and carry “pathogens to currently uncontacted people.”

In the end, Hill says, the fate of the newly contacted people may depend on whether FUNAI is willing to provide long-term medical monitoring and assistance, as well as a parcel of land that they can call their own. “So often in the past, people have been abandoned,” says Fiona Watson, research director of Survival International, a nongovernmental organization based in London. “And that first year of contact is extremely important, because that’s when you see these astronomically high figures of people dying.”

More details about the tribe are likely to emerge soon, but there is little doubt, Hill says, that these people “would like interaction with more humans on the planet.” Interviews with small populations generally show that they “remain isolated out of fear, not from some deep desire to avoid all other human societies.”