Filarioidea

Dirofilaria immitus - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine

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