Nematoda

Pseudocoelomates. Body cavity present but not lined by mesoderm. Mostly free living but parasites occur in plants and a variety of animal groups.

Encased in a cuticle which is moulted. Go through 5 stages separated by 4 moults.

Parasitic Dorylaimida

• Free living predaceous soil dwellers.

• Parasitic lineages – Mermithida – Trichurida – Dioctophymatida – Muspiceida

Mermithida: parasites of arthropods

• Adults free living (sometimes non feeding). Mate in external environment. Females contaminate host habitat with eggs. Larvae (J1) infect insects and develop to J4 or adult in host.

Muspiceida

•  Parasites of diverse hosts: mice, bats, reindeer, Kangaroo, Koala, Crows.

•  Biology poorly known.

Trichurida

• Prominent stichosome: glandular structure associated with oesophagus.

•  Includes: –  Trichinella spp.: muscle and intestinal mucosa/

submucosa –  Trichuris spp.: Intestinal submucosa

–  Capillaria spp.: variety of sites including intestinal submucosa

Trichinella

• Parasites of scavenging life cycles: involving swine, carnivora (e.g. bear, hyaena), rats, depending on species.

• Humans a frequent accidental host especially of T. Spiralis.

Capillaria • Parasites of various tissues of all

classes of vertebrates. • Capillaria philippinensis an

accidental parasite in humans in Philippines.

Life cycles varied: some direct, some involve intermediate hosts.

Trichuris

• Parasites in the submucosa of the posterior gut of mammals.

• Anterior end embedded in tissues: posterior end in lumen.

• Direct life cycle

• Trichuris trichuri in humans; may attain very high intensities (1000+ worms); rectal prolapse, finger clubbing

• T. vulpis in dogs.

• T. suis in swine.

• T. muris in mice.