Dracunculus insignis is found mainly in the subcutaneous connective tissues of the legs of raccoons, mink, and other animals, including dogs, in North America and possibly other parts of the world. The females (≥300 cm long) are much longer than the males (~20 mm). They produce ulcers in the skin of their host, through which their anterior end is protruded on contact with water. They lay characteristic long, thin-tailed larvae. Water fleas ( Cyclops sp ) are the intermediate host in which infective larvae develop. Dogs become infected through ingestion of contaminated water or a paratenic host (frogs).
A copepod of the genus Cyclops ingests the first stage-larva and the parasite develops to the infective third stage-larva in about 3 weeks. It has been shown experimentally that if a tadpole ingests the infected copepod, the L3 will go to the somatic tissues and persist there throughout the development of the frog (Eberhard and Brandt, 1995, J. Parasitology 81:792-793). Thus frogs may be paratenic hosts. When the definitive host ingests the infected copepod in drinking water, the larva invades the intestinal wall and gets into the body cavity where it develops to the fourth stage-larva. Adult female worms are usually found under the skin of the extremities. The worm causes a shallow ulcer to form in the skin over the anterior end of the worm. When this ulcer comes in contact with water, the female worm extrudes her anterior end, prolapses a length of uterus, which bursts releasing first stage-larvae into the water. The prepatent period is about 309 to 410 days.
Subcutaneous, serpentine, inflammatory tracts and nonhealing, crater-like, edematous skin ulcers are seen. Infections are rare but are occasionally found in animals that have been around small lakes and bodies of shallow, stagnant water. Treatment is by careful, slow extraction of the parasite.
D medinensis, the guinea worm of parts of Africa, Asia, and the Middle East, although primarily a parasite of humans, is also found in dogs and other animals.
Administration of miridazole or benzimidazole compounds may be useful. If possible surgically remove the worm. Also treat with an anthelmintic to kill undeveloped worms: Ivermectin or Fenbendazole for 7 to 10 days. Anthelmintics seem to work only if given before 90 days of infection.