The “migratory serpiginous perianal rash” (ick) is classic for strongyloides, a parasitic roundworm acquired from larvae-contaminated soil. Strongyloides larvae can borrow (hence the rash) and can migrate to the GI tract and lay their eggs, which then hatch in the intestine and cause diarrhea. Treatment is Ivermectin (and if not, mebendazole/albendazole). Checking the stools for larvae is the most sensitive test. Parasite life cycles are gross.

Larva currens (Latin for racing larva) is an itchy, cutaneous condition caused by infections with Strongyloides stercoralis. It is caused by the intradermal migration of strongyloides and distinguished from cutaneous larva migrans (caused by hookworms Ancylostoma and Necator) by its rapid migration, perianal involvement and wide band of urticaria.