See also: https://pmc.ncbi.nlm.nih.gov/articles/PMC3800113/ https://pmc.ncbi.nlm.nih.gov/articles/PMC3800113/ TL;DR: hookworm eradication in the American South

See also: https://pmc.ncbi.nlm.nih.gov/articles/PMC3800113/ https://pmc.ncbi.nlm.nih.gov/articles/PMC3800113/ TL;DR: hookworm eradication in the American South substantially improved school attendance and educational outcomes in children, and may have had a nontrivial positive effect on the overall economy of the region. (In case you don't see the connection, some children had such severe hookworm infestations that they were too anemic to focus in school, or even to attend at all. Teachers' accounts specifically remark on their students' newly "rosy cheeks" - because they're no longer anemic.)