Hookworm is a parasite that causes lethargy and lower performance. It is transmitted when human waste (used as a fertilizer on fields) comes into contact with human feet (barefoot field workers) in climates where it can survive (the American South).
Almost half of the American South was infected with this parasite as of 1910, causing stereotypes about lower-class Southern people being lazy and dumb. It was only around then, after centuries of lives held back from their potential, that someone thought to figure out why and discovered hookworm.
Despite some pushback from Southerners who were offended by the accusation that they were all infected by parasites, improving conditions and a big campaign by the Rockefeller Foundation eventually wiped out the parasites, but only in the mid 20th century.
Image Attribution: Marion Post Wolcott [Public domain], via Wikimedia Commons
[…] as recently as the 1950s, hookworms were an intimate and ever-present threat for those living in the South. It was nearly impossible for the rural poor—the majority back then—to avoid hookworms […] Because iron is critical for brain function, hookworm infection could also lead to irreversible cognitive and intellectual defects. A 1926 study of Alabama school children found that the greater the number of worms that students harbored, the lower their IQ.
Areas with higher levels of hookworm infection prior to the RSC experienced greater increases in school enrollment, attendance, and literacy after the intervention. This result is robust to controlling for a variety of alternative factors […]
Hookworms live in the small intestine. Hookworm eggs are passed in the feces of an infected person. If the infected person defecates outside (near bushes, in a garden, or field) of if the feces of an infected person are used as fertilizer, eggs are deposited on soil. They can then mature and hatch, releasing larvae (immature worms). The larvae mature into a form that can penetrate the skin of humans. Hookworm infection is mainly acquired by walking barefoot on contaminated soil.
Southerners initially distrusted RSC efforts. Many were offended by accusations of infection and refused to accept testing and the treatment of Epsom salts and thymol. Others believed that the disease simply did not exist. Regional newspaper editorials also strongly criticized RSC employees and viewed them as a Northern imposition.
The Rockefeller Foundation