Nematodes are similar to, but considerably distinct from, the various species of tapeworm that are parasitic and infect humans in a similar manner.
Nematodes typically infect humans via consumption of contaminated animal products or water, although any vector by which the nematode or its eggs is able to enter the intestine of the host is likely to be as good as any other. In the intestine, the nematode is able to absorb nutrients from the host because those nutrients are already in an easily-digestible state. Furthermore, the nematode has relatively easy access to the blood, and therefore the rest of the body of the host, because the intestinal wall is relatively thin compared to other parts of the body.
While the exact pathways of nematode infection may differ by species and host, the Trichinella spiralis nematode, commonly known as the pork worm, infects the muscle cells of the host via this method. Once the muscle cells are infected, virtually any portion of the host may be considered contaminated.
Parasites are organisms that live inside or on another organism (the host) and exploit that organism in some way, causing net benefit for the parasite and net deficit for the host. Parasitization of the blood itself is possible but less common than parasitization of some part of the digestive system, due to a higher concentration of nutrients.