Dracunculus medinensis

Dracunculus medinensis
Scientific classification
Kingdom:	Animalia
Phylum:	Nematoda
Class:	Secernentea
Order:	Camallanida
Superfamily:	Dracunculoidea
Family:	Dracunculidae
Genus:	Dracunculus
Species:	D. medinensis
Binomial name
Dracunculus medinensis (Linnaeus, 1758)
Synonyms
Gordius medinensis Linnaeus, 1758

Dracunculus medinensis is a nematode that causes dracunculiasis.^[1]

Dracunculiasis, also known as Guinea worm disease, is caused by the large female nematode, Dracunculus medinensis,^[2] which is among the longest nematodes infecting humans.^[3] The adult female is primarily larger than the adult male. The longest adult female recorded was 800 millimetres (31 in), while the adult male was only 40 mm (1.6 in).^[4] Mature female worms migrate along subcutaneous tissues to reach the skin below the knee, forming a painful ulcerating blister.^[3] They can also emerge from other parts of the body like the head, torso, upper extremities, buttocks, and genitalia.^[4]

Life cycle

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, intestinal wall, and enter into the abdominal cavity and retroperitoneal space. After maturing, adult male worms die while the females migrate in the subcutaneous tissues towards the surface of the skin. After about a year of infection, the female worm forms a blister on the skin, generally on the distal lower extremity (foot), which breaks open. The patient then seeks 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 becomes infectious. Ingestion of the copepods is the last stage that completes the cycle.^[5]

Disease

Main article: Dracunculiasis

Dracunculus medinensis is one of four filarial nematodes that cause subcutaneous filariasis in humans. The other three filarial nematodes are Loa loa (the African eye worm), Mansonella streptocerca, and Onchocerca volvulus (river blindness).

Epidemiology

To become infected, a person must drink water from stagnant sources (e.g., ponds) contaminated with copepods that contain immature forms of the parasite (juveniles),^[6] 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. There are no reservoir hosts, that is, each generation of worms has to pass through a human.^[4]

Pathology

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.^[4]

Diagnosis

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.^[7]

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 crustacean, or water can be boiled to make it safe to drink.

Control efforts have been highly successful via preventing contamination of drinking water and killing copepods with insecticides.^[4] 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.^[8]

Treatment

The EMS Star of Life features a rod of Asclepius

The traditional technique which involves winding the worm out on a stick has been a treatment used successfully for centuries. This treatment is memorialized in one of the modern symbols of Medicine, the Rod of Asclepius. ^[9] 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.^[4]

Eradication

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.^[10] Major progress has been made: in 1985 still 3.5 million cases were reported annually, by 2008 that number had dropped to 5,000.^[10]

Pakistan

In the 1980s 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.^[10] Other countries followed, and by 2004 the worm was eradicated in Asia.

Sudan

Eradication in Sudan had proven to be difficult, and although Carter had brought about a six-month armistice in 1995 - the "Guinea worm ceasefire"^[10] - to allow volunteers enter the region in safety, endemic sections remain.

Ghana

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 that 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 World Health Organization (WHO), UNICEF, the Japanese International Cooperation Agency (JICA), and the European Union (EU).

Etymology

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.^[11] In the 18th century, a Swedish naturalist, Carl Linnaeus, identified D. medinensis in merchants who traded along the Gulf of Guinea (West African Coast), hence the name Guinea worm.^[12]

References

1. ^ Stefanie Knopp, Ignace K. Amegbo, David M. Hamm, Hartwig Schulz-Key, Meba Banla & Peter T. Soboslay (March 2008). "Antibody and cytokine responses in Dracunculus medinensis patients at distinct states of infection". Transactions of the Royal Society of Tropical Medicine and Hygiene 102 (3): 277–283. doi:10.1016/j.trstmh.2007.12.003. PMID 18258273. http://linkinghub.elsevier.com/retrieve/pii/S0035-9203(07)00408-7. 
2. ^ Langbong Bimi (2007). "Potential vector species of Guinea worm (Dracunculus medinensis) in Northern Ghana". Vector-Borne and Zoonotic Diseases 7 (3): 324–329. doi:10.1089/vbz.2006.0622. PMID 17767406. 
3. ^ ^{a b} Talha Bin Saleem & Irfan Ahmed (2006). ""Serpent" in the breast" (PDF). Journal of Ayub Medical College Abbottabad 18 (4): 67–68. PMID 17591014. http://www.ayubmed.edu.pk/JAMC/PAST/18-4/014%20Tallah%20bin%20Saleem%20(CR).pdf. 
4. ^ ^{a b c d e f} G. D. Schmidt & L S. Roberts (2009). Larry S. Roberts & John Janovy, Jr.. ed. Foundations of Parasitology (8th ed.). McGraw-Hill. pp. 480–484. ISBN 9780071284585. 
5. ^ "Dracunculus medinensis". Centers for Disease Control and Prevention. 2009. http://www.dpd.cdc.gov/dpdx/HTML/Dracunculiasis.htm. Retrieved November 25, 2009. 
6. ^ Centers for Disease Control and Prevention (2009). "Progress toward global eradication of dracunculiasis, January 2008 – June 2009". Morbidity and Mortality Weekly Report 58 (40): 1123–1125. PMID 19834453. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5840a2.htm. 
7. ^ Z. Harrat & R. Halimi (2009). "La dracunculose d'importation : quatre cas confirmés dans le sud algérien [Imported dracunculiasis: four cases confirmed in the south of Algeria]" (in French). Bulletin de la Société de pathologie exotique 102 (2): 119–122. doi:10.3185/pathexo3352. PMID 19583036. http://www.pathexo.fr/documents/articles-bull/T102-2-3352-4p.pdf. 
8. ^ "ABATE". BASF Agricultural Products. 2006. http://www.basfpublichealth.com/products/abate.html. Retrieved December 2, 2009. 
9. ^ Blayney, Keith (Sept 2002). "The Caduceus vs. the Staff of Asclepius". Alternative Journal of Nursing July 2007, Issue 14, page 4. http://www.annals.org/cgi/content/full/138/8/673. 
10. ^ ^{a b c d} Drisdelle R. Parasites. Tales of Humanity's Most Unwelcome Guests.. Univ. of California Publ., 2010. p. 197. ISBN 978-0-520-25938-6. 
11. ^ "Guinea Worm Infection (Dracunculiasis)". The Imaging of Tropical Diseases. International Society of Radiology. 2008. http://www.isradiology.org/tropical_deseases/tmcr/chapter27/intro.htm. Retrieved December 2, 2009. 
12. ^ WikiAnswers. "Why Dracunculus Medinensis infection is called guinea worm disease?" 2009. http://wiki.answers.com/Q/Why_Dracunculus_Medinensis_infection_is_called_guinea_worm_disease (2 December 2009).