Zoonotic nematodes may cause disease in man through migrating larva (larva migrans), through direct infection or possibly through allergic responses. The parasitic genera Ancylostoma, Uncinaria, Bunostomum and Toxocara can cause larva migrans. The cod worm (Phocanema decipiens) a parasite found in fish and seals, can infect man, as can Anisakis, Dioctophyme renale and Gnathostoma hispidium larvae obtained from eating raw fish.

Trichinella spiralis occurs in marine mammals.