That happens to be the title of a pretty interesting book about hookworm in the US. The book was fine, but the story is better.
Hookworms are parasitic nematodes that take up residence in the small intestine and drink your blood. Getting there is complicated. Eggs are shed in the stool, hatch in to larvae in suitable soil, and enter the next host through bare feet. They then migrate (through the blood stream) to the lungs, then to the trachea, where they are swallowed and eventually reach the small intestine.
Enough of them can cause significant blood loss and serious anemia.
They have been a particular problem among miners, wading in wet tunnels, and an epidemic among workers in an Italian railway tunnel 1880 led to general medical understanding – other people had figured some of this out earlier, sometimes much earlier (Theodor Bilharz, even Avicenna!) but that knowledge did not become general.
Charles Wardell Styles , who had studied parasitology at the Institute Pasteur and gotten his Ph.D. at Leipzig, discovered that hookworm was common in the American South. People thought differently in those days: he tried to abolish hookworm. That was harder that he expected. Southerners claimed that they couldn’t possibly have such a disgusting problem – it was just Yankee slander. M.D.s ( back then, before the Flexner reforms, med school was often a six-month course) pointed out that he wasn’t even a doctor, so why should they listen to him? After giving one talk, two M.D.s wondered if actually getting rid of hookworm, curing the disease – wouldn’t that cut into their practice? And while he didn’t kill them on the spot, I guarantee he considered it.
Some company towns embraced hookworm eradication – they figured that outhouses and shoes were cheap, easily paid for by greater worker productivity. So various political types decided that he was a tool of the Interests, and therefore bad.
Somehow this idea reached the then-new Rockefeller foundation. They did it right. They made sure that Charles Wardell Styles was not the public face of their effort – because he didn’t suffer fools gladly, and they needed someone who positively enjoyed them, someone who could get along with the general public. They went from town to town, rather like a revival, giving people fairly unpleasant chemicals that really did get rid of most of the hookworms. Since they are small( ~1 cm) and unspectacular, they kept dead giant roundworms (up to a foot long) in a bottle and pretended that they’d been expelled from the locals. They told people to use an outhouse and wear shoes – which led some to claim that this was all an elaborate plot by John D. Rockefeller to sell shoes to innocent Southerners. On the positive side, someone came up with the idea that the South would have won the War, except for hookworm : then worming folks was a tribute to the Lost Cause.
It worked. Not perfectly, but well: greatly decreasing worm burden was good enough, since when it comes to hookworm, the dose makes the poison. A few may even be good for you, if you buy into the hygiene hypothesis.
There was another effect: it damaged the competitive position of black farmers. They’re a good deal more resistant to hookworm (it came with them, probably), and hookworm resistance was likely one of the reasons for higher labor productivity among black farmers. Reducing and then eliminating malaria had the same effect.