Remoteness didn’t protect Amazonian Tsimané from COVID-19

Indigenous Peoples have suffered disproportionally from the ongoing COVID-19 pandemic. Systemic factors including lack of sovereignty, limited infrastructure and discrimination in local health care systems make Indigenous populations vulnerable to infectious diseases. Yet little research exists to guide public health efforts tailored to remote-living Indigenous populations during global pandemics.

In Bolivia, a team of researchers and local collaborators made specific efforts to mitigate SARS-CoV-2’s impact on the Tsimané (chee-MAHN-ay), a small-scale, Indigenous society living in remote areas of the Bolivian Amazon. The effort centered on a strategy of voluntary collective isolation, a practice that restricts travel to and from Indigenous territories in the hopes that remoteness, coupled with self-sufficiency in food production and a culture of resilience, would act as a buffer against disease.

A new study by the same team tested whether voluntary collective isolation would be effective at preventing rapid spread of COVID-19 transmission among Tsimané. The authors used 20-plus years of data on population structure, movement patterns, and social networks to build a computer model that would assess the Tsimané’s vulnerability to the disease. The simulation predicted that without any intervention, approximately four out of every five Tsimané would be infected during an outbreak, and that even the most remote communities (>100 km from the nearest market town) would be affected. It also revealed that without severely curtailing travel from both outside areas and between villages, voluntary collective isolation was likely to fail.

Sadly, the researchers confirmed their model’s predictions, observing a nearly identical rate of infection across Tsimané communities in the real world, based on serological testing of individuals after a first wave of COVID-19 infections.

“Remote-living, small-scale populations are highly vulnerable to global diseases,” said Thomas Kraft, anthropologist from the University of Utah and University of California, Santa Barbara, and the lead author of the study. “We can’t rely on remoteness and voluntary isolation alone to mitigate risks—we need to a plan to direct medical resources to these communities.”

The study published on Aug. 22, 2023 in the journal PLOS Biology. 

A case study: simulation and real world

The Tsimané are one of several Indigenous tribes who hold collective title for much of the Estación Biologica del Beni and Pilón Lajas Biosphere Reserves and Indigenous Communal Lands, protected areas on the eastern flank of the Andes Mountains. The researchers designed the model to simulate the introduction of SARS-CoV-2 from the closest urban market town, and its spread among Tsimané communities. The Tsimané share characteristics common to many small-scale Indigenous societies, making this case study a useful reference for understanding infectious disease dynamics and public health interventions in other populations.

The idea for the study, published in the journal PLOS Biology, began at the outbreak of the pandemic. Many of the authors have worked with the Tsimané through the Tsimané Health and Life History Project. Senior author Michael Gurven, professor of anthropology at the UC Santa Barbara, co-founded the project back in 2002. The project operates a mobile medical team that travels between villages to provide aid, while also conducting biomedical and anthropological research. The team wanted to understand how best to direct public health messages and deploy their limited medical resources.

“At the time, there was great concern about what COVID might do if it reached the remote Amazon,” said Gurven. “So we shut down our normal operations and went into full COVID prep, hoping it wouldn’t spread. When COVID hit anyway, we then went into full surveillance mode, poised to help lessen the spread, and help treat severe cases.”

The Tsimané are mostly self-sufficient with small-scale farms of plantains, manioc, rice and corn, and by hunting and fishing. But with better roads and motorized boats, they now come into greater contact with Bolivian merchants, colonists and others in local towns. About 18,000 Tsimané live in more than 95 villages spread along rivers and logging roads—the farthest requires a multi-day boat trip to the market town. Multiple generations live together in large extended households. The close-knit community is quite social, and individuals travel frequently between villages to visit friends and family. The authors evaluated how these characteristics would influence the extent and trajectory of disease spread, the community- and individual-level risk factors for susceptibility of infection and the effect of various intervention scenarios.

“The Beni region of Bolivia is pretty remote, and medical facilities are hard to come by,” said Dr. Daniel Eid Rodriguez, a physician and medical coordinator for the Tsimané project based in Bolivia. “Any information that can help us make informed choices to best direct limited health resources are a blessing.”

To the researchers’ surprise, the remoteness of the Tsimané communities made little difference in preventing the spread of COVID-19 in both computer simulations and observed infections. Once introduced, the disease spread in a chain reaction to even the most isolated villages, as predicted by the model. The communities closest to market towns experienced infection peaks earlier than remote villages. The smaller, more isolated villages experienced the largest outbreaks proportionally, challenging the intuition that epidemics will be limited in remote, low-density populations. The authors suggest that for maximum impact, public health efforts in the future should focus on dispersing limited medical and public health messaging resources across remote communities, rather than concentrating efforts solely on denser communities closer to urban centers.

Simulations of different intervention strategies had mixed effectiveness. Restricting travel to the market town alone slowed transmission, but made essentially no difference in the final outbreak size. Even extreme travel restrictions showed limited efficacy; simultaneously reducing 90% of travel to town and between villages substantially slowed transmission but was predicted to reduce the overall proportion of adult Tsimané infected by only 15%. The model also found that if transmission rates were cut by half via social distancing or face coverings the cumulative infection in the populations was predicted to drop by 35%, as opposed to merely slowing the rate of infections via travel restrictions. Though that is a substantial impact, many local people were resistant to the use of face coverings or other interventions such as vaccines. Taken together, the team’s findings suggest that efforts that only encourage face coverings or that limit contact with urban dwellers are unlikely to control the spread of infections to Indigenous communities.

“Our work as anthropologists gives us a window into many of the processes that directly drive disease transmission,” said Kraft. “We hope that this research has allowed us to put the detailed data we collect to a practical use, such that governments, public health officials and NGOs will be better prepared to make meaningful recommendations for a more diverse array of societies when faced with the next threat.”

Other study contributors include Edmond Seabright of Mohammed Polytechnic University (MPU) and University of New Mexico; Sarah Alami of MPU and UC Santa Barbara; Samuel M. Jenness of Emory University; Paul Hooper, Daniel K. Cummings, and co-senior author Hillard Kaplan, all of Chapman University; Bret Beheim of Max Planck Institute for Evolutionary Anthropology; Helen Davis of Harvard University; Daniel Eid Rodriguez of Universidad Mayor de San Simon; Maguin Gutierrez Cayuba of Tsimane Gran Consejo; Emily Miner of UC Santa Barbara; Xavier de Lamballerie, Lucia Inchauste, and Stéphane Priet of Unité des Virus Émergents; Benjamin C. Trumble of Arizona State University; and Jonathan Stieglitz of Institute for Advanced Study.