Yesterday, I pretended to be a normal infectious disease reporter for a day and wrote about an interesting new preprint: the first report of leprosy in wild chimpanzees.
Quick thread on why this is important before I get back to covering #covid19 https://www.sciencemag.org/news/2020/11/leprosy-ancient-scourge-humans-found-assail-wild-chimpanzees

Leprosy is a facinating disease: It is ancient and everyone has an image of it (hence the terrible stigma), but at the same time we know shockingly little about it, like when and where it emerged or how exactly it spreads.

One thing people were sure of: Leprosy afflicts only humans. That has turned out to not be quite true, however. Researchers have found leprosy in squirrels in UK and in armadillos in the Americas. In both cases it’s the same genotype (3I) that apparently came from humans.

Now the chimpanzees: Researchers found some animals in Cantanhez National Park in Guinea-Bissau had terrible lesions. Later they found a similar animal in Tai National Park, hundreds of kilometers away. In both places they isolated Mycobacterium leprae from samples.

They also managed to fully sequence a M. leprae genome from each place and they are different from each other and both are rare genotypes. This and the fact that there is no prolonged contact of humans and chimps at either site argues against an infection from humans.

So in the preprint the scientists argue that their findings „challenge the long-held assumption that humans are the main reservoir of M. leprae
and suggest that this pathogen may
sporadically emerge from environmental sources“ https://www.biorxiv.org/content/10.1101/2020.11.10.374371v1

You can argue about how conclusive the evidence is, but if the researchers turn out to be right, then these sad cases in chimpanzees just pointed us to a fundamental finding about leprosy that we missed through millions of human cases.

So the scientific search for a leprosy reservoir is on: Rodents are a likely candidate, Anne Stone told me. But scientists have shown in the lab that amoeba and some insects can also carry the pathogen. @Leendertz_Lab told me that they plan to investigate all these possibilities.

What does this mean for humans?
1. If there really is a reservoir, eradicating leprosy may not be possible.
2. A new avenue for leprosy research. „It’s a very difficult disease“, @AvanziCh told me. “Any clue we can get about it from animals or anywhere is really, really helpful.”

What does it mean for chimpanzees? The four individuals in Cantanhez are doing okay, @KJHockings told me, though one is losing weight. While leprosy is apparently not as catastrophic for the animals as some respiratory viruses it is sadly yet another threat for these animals!