Filarioidea

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

Dirofilaria immitis

Onchocerca spp.

Parafilaria spp.

Setaria spp.

Elaeophora scheideri

Stephanofilaria spp.

• Filaroides osleri causes infection in tracheain gogs
• Dirofilaria immitis live in heart and pulmonary arteries of dogs and cats