In 1978, Dr. Francisco Lopera did what recent medical school graduates in Colombia and much of Latin America have long done: He set out for an obligatory year of work in a remote part of the countrylucky horse, where an inexperienced médico rural might be the only physician for miles. Dr. Lopera, who was born in the Andean region of Antioquia and knew mostly mountains and farm life before medical school, carried out his service in the Darién Gap, on the Caribbean coast near Panama.

There Dr. Lopera, a groundbreaking Colombian Alzheimer’s researcher who died this week at age 73, treated stabbings, snakebites, complicated births, burns and fevers in a hospital that had electricity for only half the day. On one occasion, he was kidnapped by Marxist guerrillas. Another time, he had to flee gunshots.

When I met Dr. Lopera in 2017, to start research on a book about the families with Alzheimer’s that became his life’s work, he told me a story about two young brothers who had died one after the other in his hospital, of unknown causes. Lopera traveled to the family home in a remote jungle clearing, where he discovered that the boys’ surviving siblings had bites on their fingers from vampire bats. He sent the bodies to a pathology lab hours away by boat, and the pathologists confirmed rabies. When the government brought in a rabies expert to investigate, Dr. Lopera joined him.

He left that experience — long nights in the rainforest, searching for hidden roosts, engrossed in the natural history of rabies and bats — wanting to become a rabies epidemiologist. But that was not to be. His interests were eclectic and quick to change, and a few years later he became a neurology resident in Medellín.

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In 1984, Dr. Lopera examined a farmer in his 40s who appeared to have dementia. Dr. Lopera took again the unusual step of traveling to the family home, in a mountain hamlet like the one where he had been born. Not just the farmer had symptoms of dementia, he saw — a brother also appeared to be affected. Dr. Lopera had discovered what would turn out to be the world’s largest family with early-onset Alzheimer’s disease. The family shared a genetic mutation, later nicknamed the paisa mutation, that was unique to their region of Colombia. Dr. Lopera spent the next four decades studying the family’s 6,000 members.

ImageDr. Francisco Lopera, second from right, in Yarumal, Colombia, in 2010, with Oderis Villegas, center, who was showing signs of Alzheimer’s disease at age 50. A sister, María Elsy, left, had a more advanced case.Credit...Todd Heisler/The New York Times

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