INTRODUCTION Dracunculus medinensis ( Guinea worm)

Dracunculus medinensis is a nematode that causes 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).

Dracunculiasis Dracunculiasis, also known as Guinea worm disease, is caused by the large female nematode, Dracunculus medinensis, which is among the longest nematodes infecting humans.

Morphology The adult female long, cylindrical worm with smooth cuticle resembling a long piece of white twine. It has a blunt anterior end and a tapering recurved tail. It measure about 60 to 120 cm in length and 1 to 2 mm in thickness. It is the longest nematode. The male is which is rarely seen is much small 10 to 40mm long and 0.4 mm thick. The larva measures 55 to 750 μm in length and 15 to 25 μm in breath. The larva swims about with a coil and uncoiling motion.

Life cycle Human are the definitive host. There is no animal reservoir. Adult worm which is a viviparous discharged larvae , which are ingested by the fresh water crustacean Cyclops which is the intermediate host

Life cycle Humans become infected by drinking unfiltered water containing copepods (small crustaceans; water fleas) that have been infected with D. medinensis larvae. The infective form is the third-stage larva present in the haemocoele of infective Cyclops. Water fleas digested by stomach acid but not the 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.

Cont…(life cycle) 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. The infected person develops the blister and attendent clinical manifestation at about same time of the year

Pathogenicity and clinical features Incubation period is one year Infection induce no illness till the gravid female come s to lie under the skin ready to discharge its embryos Few hours before the development of blister symptom's includes nausea, vomiting, intensive pruritus, and urticarial rash. The blister develop as a reddish papule with vesicular centre and surrounding indurations. The most common sites are on the fee between the metatarsal bones or on the ankles. The local discomfort diminished with release of the embryo, the worm happens to break out and cause intensive inflammation, with cellulitis,, secondary infection may follow. Sometimes the worm may travel to unusual site such as pericardium, the spinal canal or the eyes with serious effect.

Epidemiology When a person drinks water from stagnant sources (e.g., ponds) contaminated with copepods that contain immature forms of the parasite (juveniles),gets infected , which have been previously released from the skin of a definitive host.

Cont…(epidimiology) 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. Paratenic host- organism which act as an intermediate host. Halps into finishing the life cycle of a parasite

It does take almost ten days for the worm to move out completely

CONT… 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. By bathing the ulcer with water the worm can release the embryo which can be examined under the microscope. Calcified worm can be seen by radiograph Intradermal test with the guinea worm antigen elicits positivr response

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.

CONT… Control efforts have been highly successful via 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.

Treatment 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.

THE ROD OF ASCELPIUS

Worm wound on a stick

CONT…(TREATMENT) 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.

ERADICATION Dracunculiasis, a disease unique to humans, can be eradicated by providing safe water supply which prevents D. medinensis from completing its life cycle.

REFERENCES G. D. Schmidt & L S. Roberts (2009). Larry S. Roberts & John Janovy, Jr.. ed. Foundations of Parasitology (8th ed.). McGraw-Hill. pp. 480–484.  www.wikipedia.com www.medicinenet.com biomedicalephemera.tumblr.com