Gordius medinensis Linnaeus, 1758
Dracunculus medinensis is a nematode that causes dracunculiasis, also known as guinea worm disease. The disease is caused by the large female nematode of D. medinensis, which is among the longest nematodes infecting humans. The adult female is primarily larger than the adult male. The longest adult female recorded was 800 mm (31 in), while the adult male was only 40 mm (1.6 in). Mature female worms migrate along subcutaneous tissues to reach the skin below the knee, forming a painful ulcerating blister. They can also emerge from other parts of the body, such as the head, torso, upper extremities, buttocks, and genitalia.
Humans become infected by drinking unfiltered water containing copepods (small crustaceans) that have been infected with D. medinensis larvae. After ingestion, the copepods die and release the stage 3 larvae, which then penetrate the host's stomach or intestinal wall, and enter into the abdominal cavity and retroperitoneal space. After maturing, they mate and adult male worms die. Approximately one year after mating the fertilized females migrate in the subcutaneous tissues towards the surface of the skin causing formation of blisters on the skin, generally on the distal lower extremity (foot), which breaks open. The patients then seek to relieve the local discomfort by placing their foot in water, but when the lesion comes into contact with water, the female worm emerges and releases her stage 1 larvae. The larvae are then ingested by a copepod, and after two weeks (and two molts), the stage 3 larvae become infectious. Ingestion of the copepods is the last stage to complete the cycle.
A person gets infected, by drinking water from stagnant sources (e.g., ponds) contaminated with copepods containing immature forms of the parasite (juveniles), which have been previously released from the skin of a definitive host. The infection can also be acquired by eating a fish paratenic host, but this is rare. The parasite is known to be found in Africa and India. No reservoir hosts are known, that is, each generation of worms must pass through a human.
Female worms elicit allergic reactions during blister formation as they migrate to the skin, causing an intense, burning pain. Such allergic reactions produce rashes, nausea, diarrhea, dizziness, and localized edema. Upon rupture of the blister, allergic reactions subside, but skin ulcers form, through which the worm can protrude. Only when the worm is removed is healing complete. Death of adult worms in joints can lead to arthritis and paralysis in the spinal cord.
Diagnosis of dracunculiasis is made by direct observation of the worms emerging from the lesions appearing on the legs of infected individuals and by microscopic examinations of the larvae.
Prevention and control
Guinea worm disease is transmitted via drinking contaminated water. A fine-mesh cloth filter, such as nylon, can be used to remove the diseased worm-containing crustaceans, or water can be boiled to make it safe to drink.
Control efforts have been highly successful by preventing contamination of drinking water and killing copepods with insecticides. Water sources can be treated with an approved larvicide that kills copepods, such as Abate, without posing a great risk to humans or other wildlife.
The traditional technique, winding the worm out on a stick, has been a successful treatment for centuries. An alternative method is done by surgically removing the worm. The surgical procedure is only successful if the entire worm is near the surface of the skin. Drugs such as metronidazole may relieve symptoms, but activity against the worm remains questionable.
Dracunculiasis, a disease unique to humans, can be eradicated by providing safe water supply which prevents D. medinensis from completing its life cycle. In 1984, the World Health Organization (WHO) asked the Centers for Disease Control and Prevention (CDC) to spearhead the effort of its eradication, an effort that was further supported by the Carter Center. Major progress has been made; in 1985, 3.5 million cases were still reported annually, but by 2008, the number had dropped to 5,000. This number further dropped to 1060 in 2011 and a mere 5 cases reported in the first few months of 2012.
In the 1980s, former U.S. President Jimmy Carter persuaded President Zia al-Haq of Pakistan to accept the proposal of the eradication program, and by 1993, Pakistan was free of the disease. Key to the effort was, according to Carter, the work of "village volunteers" who educated people about the need to filter drinking water. Other countries followed, and by 2004, the worm was eradicated in Asia.
Eradication in Sudan had proven to be difficult, and although Carter had brought about a six-month armistice in 1995—the "Guinea worm ceasefire"—to allow volunteers enter the region in safety, but endemic sections remain.
Ghana is winning the battle against the Guinea worm disease, recording a zero infection rate in the month of November 2009. In the year 2008, 501 new cases were recorded, against 3,357 cases in 2007, representing about an 85% reduction. A number of interventions in the previous two years had been pursued, including monitoring dams and other sources of drinking water in endemic communities to ensure infected people did not contaminate the water sources. Additionally, filters and other water treatment equipment were provided at both water pumping sites and homes to treat water before drinking. This is all due to the efforts of the National Guinea Worm Eradication Program, funded by the WHO, UNICEF, the Japanese International Cooperation Agency, and the European Union.
Guinea worm disease has been eradicated from India. Rajasthan was severely affected by dracunculiasis, especially southern Rajasthan (Dungarpur, Banswara and Udaipur districts), and was hyperendemic about two decades ago. The alarming status of the guinea worm led to the launching of the SWACH project by the government in 1986. This project assured proper sanitation and supply of clean and hygienic potable water to the residents of endemic areas and, as expected, it was a huge success. Owing to the success of the SWACH project, a decade later, the State Government declared Rajasthan rid of Dracunculus. But, every species struggles for its existence, and so did Dracunculus. In 2002 and 2003, two cases of dracunculiasis were reported from Dungarpur and Banswara districts.
Dracunculiasis once plagued a wide band of tropical countries in Africa and Asia. Its Latin name, Dracunculus medinensis, ("little dragon from Medina") derives from its one-time high incidence in the city of Medina, and its common name, Guinea worm, is due to a similar past high incidence along the Guinea coast of West Africa; both of these locations are now free of Guinea worm. In the 18th century, Swedish naturalist Carl Linnaeus identified D. medinensis in merchants who traded along the Gulf of Guinea (West African Coast), hence the name Guinea worm.
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