Dracunculus medinensis Taxonomy, Common Name, Disease
• CLASS: SECERNENTEA • SUBCLASS: SPIRURIA • ORDER: SPIRURIDA • SUPERFAMILY: DRACUNCULOIDEA • FAMILY: DRACUNCULIDAE
Scientific name - Dracunculus medinensis
Common name - Guinea worm, medina worm, serpent worm Historical
This nematode was known as a parasite of humans about 1530 B.C. Some investigators suggest that the Guinea worm is the "fiery serpent" referred to in the Bible. The symbol of a Physician is the "Caduceus". This is the staff of Hermes and contains coiled serpents on a staff. The serpents are believed to represent the Guinea worm. Hosts
Humans. Distribution
Asia (India, Iran, Pakistan, Afghanistan, Turkestan, USSR), Africa (Nile Valley, Central Africa, East Africa), Indonesia, Fiji, Brazil. Life Cycle
The adult females are found in superficial subcutaneous tissues of the legs, arms and sometimes the abdomen. A blister develops on the skin of the host near the location of the head of the nematode. When this blister breaks the body wall and uterus of the nematode at the site of the opening in the hosts skin bursts. When this area is exposed to water the female nematode discharges numerous first stage juveniles into the water (ovoviviparous). These juveniles must be ingested by the intermediate host, a copepod, in order to continue development. The ingested first stage juveniles pass from the digestive tract of the copepod to the coelom where they develop to second stage and then to third stage infective juveniles which are coiled and sheathed (retain the cuticle of the second-stage juveniles). The life cycle can continue only if the copepod intermediate host is ingested by the definitive host. After ingestion the nematode juveniles are released from the copepod and they migrate via the lymphatics to deep subcutaneous tissues where they develop to adult nematodes. Approximately one year after infection takes place (one year after ingestion of the copepod intermediate host) the adult female nematode migrates to the superficial subcutaneous tissues. During the time that the nematode is developing and growing in deep body tissue there are no symptoms associated with the infection. Guinea worm infections occur primarily in areas with low rainfall or in areas where rainfall is seasonal. The pattern of infection is related to the availability of water. Most infections take place near the end of the dry season when water for culinary purposes is found in small pools and stepwells. At this time the intermediate host copepods are present in larger numbers. This increases the chance of infected persons with adult worms coming in contact with water and the subsequent discharge of the first stage juveniles into a pool or well. Symptoms-Pathogenicity
When the adult female migrates to superficial cutaneous tissues some symptoms become evident due to the release of toxic substances. A few hours before the beginning of the formation of the blister in the immediate vicinity of the nematode's head the following symptoms may be present: (1) a rash accompanied by severe itching, (2) nausea, (3) vomiting, (4) diarrhea, and (5) dizziness. These symptoms continue until the blister is formed and has broken and toxic fluids contained in the blister have drained away. However, the opening can become infected by bacteria and this infection can extend into the tunnel occupied by the adult female. There may be later symptoms-- fibrosis of the skin, muscles, tendons and joints which may or may not interfere with locomotion or use of limbs. Management
Avoid drinking water containing copepods. Filtering water, or treatment of water with chlorine will remove or kill the intermediate host. Boiling water kills the intermediate host. Bathing and wading in drinking water should be avoided.
Individuals with infections may have the worms extracted mechanically when the adult worms are near the surface of the skin. Drugs are available that will kill the developing worms in the definitive host. In 1947 it was estimated that there were 48 million human infections by the Guinea Worm. Fifteen million of these were in Africa and 30 million in Asia. Surgery to remove adult worms. Importance
In addition to its historical importance and the disease it causes, this group of nematodes is thought to be transitional between parasites of the digestive tract, and filarial parasites of tissues. Characteristics
Dracunculus medinensis is one of the largest nematodes known. Adult females have been recorded up to 800 mm long, although the few males known do not exceed 40 mm. The mouth is small and triangular and is surrounded by a quadrangular, sclerotized plate. Lips are absent. Cephalic papillae are arranged in an outer circle of four double papillae at about the same level as the amphids and an inner circle of two double papillae, which are peculiar in that they are dorsal and ventral. The esophagus has a large glandular portion that protrudes and lies alongside the thin muscular portion. In the female the vulva is about equatorial in young worms; it is atrophied and nonfunctional in adults. The gravid uterus has an anterior and a posterior branch, each of which is filled with hundred of thousands of embryos. The intestine becomes squashed and nonfunctional as a result of the pressure of the uterus. Spicules of the male are unequal and 490 to 730 um long. The gubernaculum ranges from 115 to 130 um long. Genital papillae vary considerably in published descriptions. References
1. Schmidt, G.S., and L.S. Roberts. 1989. Chapter 30. Order Camallanata: Guinea Worms and Others. in Foundations of Parasitology. Times Mirror/Mosby College Publishing. St. Louis. 750 pages. 2. Levine, N.D. 1968. Nematode Parasites of Domestic Animals and of Man. Burgess Publishing Company. Minneapolis. 600 pages. 3. Olson, O.W. 1974. Animal Parasites Their Life Cycles and Ecology. Dover Publications Inc., New York. 562 pages.