After reading the article, I’m confused about how it works. Guinea worms are parasites that you get infected with from bad water sources. Unless you eradicate the source (e.g. the worms themselves), can you really say that you’ve eradicated the disease?

Many diseases can likely never be eradicated because they have a natural reservoir, some wild population of animal species in which the disease normally propagates. A natural reservoir will keep the disease in circulation and reinfection of humans can occur from contact with species in the natural reservoir. Ebola virus is like that, it keeps popping up now and then because it has a natural reservoir (believed to be fruit bats).

Guinea worms isn’t like that, which is part of why it’s a strong candidate for eradication. Its reproductive cycle has a step that primarily goes through people or dogs, neither of which would be considered a natural reservoir:

As such, if we reach a state where there are no infected people or dogs then guinea worm could go extinct. There would be larvae left in the wild at that point, but as long as those larvae don’t infect a suitable host then they never become worms. No new worms means no new larvae, and larvae have a fairly short lifespan so we would only need to maintain that situation for maybe a few years before we could confidently say that guinea worm has been eradicated (i.e. any remaining larvae must be dead by that point).