Chimps in two West African sites suffer from leprosy, a disease never before documented in wild chimpanzees. The strains in each park appear unrelated, and they are unlikely to have come from contact with humans, the authors argue. The finding could indicate an unknown source of leprosy in the wild and reveal new clues about a still-mysterious disease.

For years, researchers thought leprosy afflicted only humans. But over the past 2 decades, scientists have also found the pathogen circulating in nine-banded armadillos in the Americas and in red squirrels in the United Kingdom. Both species harbor the same bacterial genotype, called 3I, that has been linked to human infections in medieval Europe. In both cases, the pathogen appears to have jumped from humans to the animals. Scientists have also reported isolated leprosy cases in captive animals, including chimps.

Human diseases can spill over to chimpanzees with devastating consequences. But researchers think a recent transmission of leprosy from humans to chimps is unlikely, because the disease usually spreads only after prolonged, close contact, and there have been no known leprosy cases among researchers or local assistants. (Although researchers study the chimps, they keep at least 6 meters of distance.) In addition, the genotypes responsible for both outbreaks are rare in humans, the researchers report today on the preprint server bioRxiv. Leendertz will not rule out two separate, ancient infections from humans. But, he concludes, “The most likely scenario is that there is some unidentified leprosy reservoir.”

Photo: Tai Chimpanzee Project