Scientists Discover Leprosy in West-African Primates

Two West-African Chimpanzees (Tambako the Jaguar)

A group of scientists working in West Africa discovered trace infections of leprosy among the local chimpanzee population, according to a paper published on November 11. Previously, scientists were under the impression that leprosy only infected humans and small mammals—such as nine-banded armadillos in the United States and red squirrels in the United Kingdom. 

The team studied wild chimpanzees in Cantanhez National Park in Guinea-Bissau and Taï National Park in the Côte d’Ivoire. Analyzing several hundred thousand photos, the scientists discovered trace nodules, hair loss, and hypopigmentation on the chimpanzees, signifying a M. leprae infection. Additionally, through the use of PCR testing on fecal samples, the team was able to confirm their hypothesis. 

Previous reports indicate that leprosy has infected other species before. In 2009, a West African chimpanzee was mauled by a leopard, and when the scientists tested her spleen samples with PCR, they discovered that she was positive for M. leprae. However, the scientific consensus until now was that leprosy was mostly a human-adapted pathogen. Therefore, the prime hypothesis was a human-to-primate spillover. 

The scientists, however, point to several flaws in this theory. First, the chimpanzees in the Cantanhez National Park seldom come into contact with humans, reducing the likelihood of a spillover event. Furthermore, the M. leprae genotypes discovered in West Africa are rare and do not usually occur in humans, casting doubt on their earlier hypothesis. 

Fabian Leendertz, a veterinarian employed by the Robert Koch Institute in Berlin, says, “the most likely scenario is that there is some unidentified leprosy reservoir.” Furthermore, Anne Stone, an evolutionary geneticist at Arizona State University, claims that “the data increasingly points to the possibility that something else than humans is actually the main host.” 

At the moment, scientists believe that an environmental source may be at play. M. leprae is able to replicate in amoebas, arthropods, and ticks. However, the exact etiology of leprosy remains unknown, leading to fervent speculation among the scientific community. 

The fate of the infected West African chimpanzees remains unknown. Leendertz says, “Humans have to take antibiotics for months to treat leprosy. You just can’t do that with these wild animals.” Fortunately, leprosy does not pose a grave threat to chimpanzee communities, “but it’s an additional threat, of course, on top of poaching, habitat loss, and other diseases,” asserts Leendertz.