Dracunculus medinensis Medina worm
The clinical syndrome was well known in ancient Egypt and during the Greek and Roman periods. It is found in many areas throughout the world and is a parasite of dogs and other carnivores in North America. Although the worms are very long and thin, they are not true filarial worms, but are grouped in their own order.
Life Cycle and Morphology
Human infection is acquired from ingestion of infected copepods (water fleas). The released larvae penetrate the duodenal mucosa and develop in the loose connective tissue.
The worms are very long, with the females measuring up to a meter in length by 2 mm in width. The male is much smaller and inconspicuous (2 cm long). The worms mature in the deep connective tissue and the females migrate to the subcutaneous tissues when they are
gravid and contain coiled uteri filled with rhabditiform larvae. Maturation takes approximately 1 year. At this stage in the life cycle the female migrates to the skin and a papule is formed in the dermis, usually by the ankles or feet (although they can be anywhere on the body). The papule changes into a blister within 24 hours to several days.
Eventually the blister ulcerates and, on contact with fresh water, a portion of the uterus prolapses through the worm's body wall, bursts open, and discharges many larvae into the water. This may happen several times until all the larvae are discharged. The larvae are then ingested by an appropriate species of Cyclops. Development takes about 8 days before the larvae are infective for humans.
Clinical Disease
After ingestion of an infected copepod, no specific pathology is associated with larval penetration into the deep connective tissues and maturation of the worms. Once the gravid female begins to migrate to the skin, there may be some erythema and tenderness in the area where the blister will form. Several hours before blister formation the patient may exhibit some systemic reactions, including an urticarial rash, intense pruritis, nausea, vomiting, diarrhea, or asthmatic attacks. The lesion develops as a reddish papule, measuring 2 to 7 cm. Symptoms usually subside when the lesion ruptures, discharging both the larvae and worm metabolites.
If the worms are removed at this time, healing usually occurs with no problems. If the worm is damaged or broken during removal, there may be an intense inflammatory reaction with possible cellulitis along the worm's migratory track. If secondary infection occurs, there may be serious sequelae, including arthritis, synovitis, and other symptoms, depending on the site of the lesion.
Diagnosis
Diagnosis can be confirmed at the time the cutaneous lesion forms with subsequent appearance of the adult worm. Infected lesions would have to be distinguished from carbuncles, deep cellulitis, focal myositis or periostitis, or even rheumatism. Using x-rays, calcified worms may also be found in subcutaneous tissues. They may appear as linear densities (up to 25 cm), tightly coiled structures or sometimes nodules.
Epidemiology and Prevention
Disease transmission depends on several factors: (1) water sources where Cyclops breed, (2) direct water contact with infected humans, and (3) use of this water source for drinking. In various parts of the world, certain types of water sources provide all the above transmission requirements, e.g., step wells in India, covered cisterns in Iran, and ponds in Ghana. The disease can be eliminated within 1 to 2 years with safe drinking water.
