Parasitic nematodes have adapted part of all of their life cycle inside a host animal or plant. In contrast to free-living nematodes, these have varying requirements for support and shelter from the external environment. Infection occurs either through ingestion of mature eggs or larvae or through penetration of skin by nematode larvae or insect vectors. The variety of nematode parasites is truly amazing. The are a common cause of intestinal infection but can also penetrate tissues and inflict significant damage.
Intestinal infections are often subclinical, and disease is only apparent after heavy infection.
Mortality is attributable to complications of high parasitic infestations.