Nematodes

Round-shaped endoparasites

Nematodes, or roundworms, are, as their name indicates, round worms of varying sizes, which live in the intestine of their host. They attach themselves via their lip-disks or hooks to the wall of the intestine and feed on mucous, blood or intestinal contents.

Development without intermediate host

The development of nematodes does not include an intermediate host. The eggs or larvae are consumed by the same species that they came from. The larvae frequently travel through the body, particularly the lungs, while they develop. The final larval stage returns to the intestines, where they metamorphose into adult roundworms and begin egg production.

False hosts

Man (a false host) can also be infected by the eggs and suffer from migrans vesceralis syndrome caused by the larvae. The traveling larvae reach all organ systems through the blood stream. They then encapsulate themselves in the connective tissue. Symptoms are different depending on the affected organs, but include hepatomegaly, asthma-like symptoms and central nervous system disorders and lameness.

Intrauterine and galactogenic infection

A further method of transmission of roundworms is intrauterine and galactogenic infection. Dormant larvae in the mother's muscle tissue are activated by the mother's hormones. Hence roundworm infections are typically a problem in young animals, which suffer from intestinal and pulmonary afflictions. As they grow older, the animals develop immunity which protects them from most roundworm infections.

Learn more about nematodes species infecting cats, dogs and horses.