Guinea worm is close to becoming the second disease ever wiped out

Guinea worm is a parasite you swallow in unclean water. A year later a metre-long worm burns its way out through the skin, disabling people for weeks, often right at harvest time. There is no drug and no vaccine. The only tools are teaching people to filter their water and keeping the sick from wading back into it.

A global campaign led by the WHO and the Carter Center began in the 1980s, and reported cases fell from hundreds of thousands to a handful. Early figures understate the true burden, because surveillance was patchy before the campaign, so the reported peak of 892,055 in 1989 reflects better counting as much as a worse year. The last stretch is the hardest: a few cases still surface, in people and now in dogs, so the disease has not yet been certified as gone.