It’s mentioned in the article it’s been documented in Central America for more than ten years in manual laborers but with few clues - possibly genetic predisposition combined with heat and physical exertion. It’s different types of manual labor so toxin exposure seems unlikely unless it turns out all of them got poisoned doing the same type of manual labor at one point and I would speculate they would have figured it out by now in Central America if it was toxin exposure.

https://www.npr.org/sections/goatsandsoda/2019/08/26/7538343...