Threadworm-- Any long, thin nematode worm.

50 centimeters

Threadworm infection, which is also called strongyloidiasis, occurs in most countries of the world but is natural to (endemic in) tropical and subtropical climates.

You catch threadworm by ingesting an egg, or by having an egg enter your body via the anus. Sounds a bit gross, but it happens. The best way to prevent threadworm is to practice hygiene. It can become a problem if feces isn't disposed of correctly in an area, but developed countries don't generally have to worry about that sort of issue.

Anthelmintics are use in the treatment of threadworm infections and include mebendazole and piperazine