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.).
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== General Appearance ==
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*Non-bursate
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*Typically, they are long (up to 12cm or more), but filamentous
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*Live in connective tissues
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**The most important veterinary species is ''Dirofilaria immitis'' which lives in the right heart and pulmonary arteries
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== General Life-Cycle ==
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*The females of most species do not produce eggs, but instead they produce motile embryos ('''microfilariae''')
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*Female worm → microfilariae → accumulate in blood or tissue fluid
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→ taken up by biting arthropod intermediate host
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→ L1 → L2 → L3
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→ enters wound
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→ larvae develop and migrate to predilection site in final host