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The filarial worms are of great importance in human medicine in the tropics, causing diseases such as elephantitis and river blindness, but their veterinary interest is limited - with the important exception of Dirofilaria, the canine heartworm, which is a major cause of morbidity and death in warmer, humid regions (including parts of the USA, Australia, southern Europe etc.).
General Appearance
- Non-bursate.
- Typically, they are long (up to 12cm or more), but filamentous.
- Live in connective tissues.
- (The most important veterinary species is Dirofilaria immitis which lives in the right heart and pulmonary arteries).
General Life-Cycle
- The females of most species do not produce eggs, but instead they produce motile embryos (microfilariae).
- Female worm → microfilariae → accumulate in blood or tissue fluid
→ taken up by biting arthropod intermediate host
→ L1 → L2 → L3
→ enters wound
→ larvae develop and migrate to predilection site in final host.
- Filaroides osleri causes infection in trachea
- Dirofilaria immitis live in heart and pulmonary arteries of dogs and cats