In the South American Amazon basin, the first sign of a catastrophe is often invisible to the outside world. It begins with a single fever in a remote village, a shift in local wildlife patterns, or a sudden cluster of respiratory distress cases in a rural clinic. By the time these signals reach a national capital, it is often too late to prevent a localized outbreak from becoming a regional crisis. 

In 2024-2025, there was a concerning resurgence of infectious diseases threatening the vulnerable indigenous populations living in the Amazon basin. This included a sharp increase in yellow fever cases across Brazil, Colombia, Peru, and Bolivia; a massive 34-fold increase in pertussis cases in Brazil’s Yanomami Indigenous Territory compared to the previous year; and the emergence of Oropouche virus outbreaks in Peru’s Loreto region and parts of Brazil. 

These outbreaks highlight the critical need for specialized field epidemiology-trained personnel capable of rapid detection and response in remote, high-risk, and vulnerable areas. Field epidemiologists, also known as disease detectives, operate under the framework of “First In, Last Out.” They aim to understand how and why a health threat is occurring, who is affected, how to stop its spread, how to implement public health interventions, and, finally, which disease surveillance system is most effective for detecting future outbreaks.

In January 2025, a report from a rural clinic in the Imaza District of Bagua Province, Peru, prompted a swift, coordinated response by district public health authorities. A member of the Awajún indigenous community presented with symptoms of fever, malaise, and jaundice, alerting authorities to a suspected case of yellow fever. A single case among the Awajún people exposed a dire vulnerability: more than 90% of the population remains unvaccinated against the disease. Yellow fever is a highly lethal disease, with a case-fatality rate of 60% in severe cases.

Within 24 hours of the outbreak notification, Lenin Yonel La Torre Rosillo, a Bagua District Epidemiologist and Advanced Field Epidemiology Training Program (FETP) graduate, was on his way to the field as lead for the Rapid Response Team (RRT). Also on the team were colleagues Cleider Oblitas Cabrera, an FETP fellow, and Jorge Junes, an FETP graduate.

“The true magnitude of the event was unknown, the risk of spread was high, and the people at risk lived in a remote, difficult-to-access area,” said La Torre Rosillo. “Recent heavy rains had increased the flow of the Marañón River, making travel to the site a significant logistical challenge.”

The RRT team’s “first in” response upon arriving in the Awajún village as first responders was instrumental in mitigating the outbreak’s severity. After La Torre Rosillo and his team arrived, an additional four cases of yellow fever were confirmed. Through early detection and contact tracing, 48 people were monitored over the six months of the outbreak. In the end, 17 were confirmed to have yellow fever. 

The team coordinated with local indigenous leaders, organizing community meetings and, through pictures and Awajún-translated materials, encouraging them to accept vaccination as the most effective preventive measure to combat the spread of yellow fever. 

Beyond the numbers, structural change was achieved for the Awajún: community epidemiological surveillance was strengthened, and vaccination coverage increased from 10% to nearly 95%. 

Lenin Yonel La Torre Rosillo’s expertise is the result of an intensive strategy to scale up the number of FETP-trained public health workers in South America since 2020. Peru is one of eight nations alongside Argentina, Brazil, Chile, Colombia, Ecuador, Paraguay, and Uruguay that form the South American Field Epidemiology Network (REDSUR). 

In collaboration with the U.S. CDC, The Task Force’s Training in Epidemiology and Public Health Interventions Network (TEPHINET) helped establish and expand FETPs in REDSUR. While the U.S. CDC provides funding and technical expertise, TEPHINET handles coordination, technical, and implementation support needed to establish new programs and add tiers to existing ones. The FETP “tiered” approach strengthens the public health workforce at all levels. While Advanced FETP (a two-year program) develops national and regional expertise, the Intermediate and Frontline programs empower district and local-level staff to catch outbreaks before they escalate.

The collaborative efforts of TEPHINET, REDSUR, and the U.S. CDC create a supportive environment that enhances the capacity, relevance, and impact of FETPs in South America, contributing to their long-term sustainability. 

Reflecting on these efforts, TEPHINET’s Director, Dr. Carl Reddy, said, “The detection and successful management of outbreaks is contingent upon collaboration where all partners are committed to alleviating unnecessary pain and suffering.”