Parasitology-Dracunculus Medinensis

MORPHLOGY Dracunculiasis, also known as Guinea worm disease, is caused by the large female nematode, Dracunculus 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. EPIDEMIOLOGY 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. 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 or 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 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 becomes infectious. Ingestion of the copepods is the last stage to complete the cycle.

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.

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. TREATMENT 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.

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.

REFERENCES “Guinea Worm Infection (Dracunculiasis)”. The Imaging of Tropical Diseases. International Society of Radiology. 2008. 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 Centers for Disease Control and Prevention (2009). “Progress toward global eradication of Dracunculiasis”, January 2008 – June 2009.

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