Nematodes are commonly called roundworms because, as the name suggests, they are round
when viewed in cross section. However, they are in fact cylindrical in structure and taper
towards their anterior and posterior ends. They are bilaterally symmetrical, and while the
sexes are separate in most species, a few are hermaphrodite. Nematodes that parasitize our
domestic animals are found in all parts of the body but are most commonly found in the
digestive and respiratory tracts and the circulatory system.
Nematode parasites of domestic animals vary greatly in size ranging from small
hair-like worms (up to 2 cm long) in the Superfamily Trichostrongyloidea to large, robust
worms ( up to 40cm long) in the Superfamily Ascaridoidea. The following six examples show
the considerable variations in size and appearance seen among the nematodes
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| Species: |
Toxocara canis |
Dirofilaria immitis |
Trichostrongylus axei |
| Superfamily: |
Ascaridoidea |
Filarioidea |
Trichostrongyloidea |
| Order: |
Ascaridida |
Spirurida |
Strongylida |
| Location: |
Small intestine |
Right heart, pulmonary arteries |
Abomasum/stomach |
| Hosts: |
Dogs |
Dogs, cats, ferrets |
Ruminants, horses, swine |
| Size: |
10 - 18 cm |
23 - 30 cm |
0.7 cm |
