DRACUNCULUS MEDINENSIS Flashcards
DRACUNCULUS MEDINENSIS COMMON NAME AND HISTORY
Common name: Guinea Worm
History and Distribution
=The guinea worm has been known from antiquity. It is believed to have been the ‘fiery serpent’ in the Bible, which tormented the Israelites on the banks of the Red Sea.
=The technique of extracting the worm by twisting it on a stick, still practized by patients in endemic areas is said to have been devised by Moses.
=The picture of the ‘serpent worm’ on a stick may have given rise to the physician’s symbol of caduceus.
=Galen named the disease dracontiasis, (Greek dracodragon or serpent). Avicenna called it the Medina worm as it was prevalent there. Hence, the name Dracunculus medinensis (Dracunculus being the diminutive of Draco).
Habitat of Dracunculus medinensis
=The adult females of D. medinensis are usually found in the subcutaneous tissue of the legs, arms and back in man.
Dracunculus medinensis epidermiology
=Was present in tropical Africa, the Middle-East in Arabia, Iraq, Iran, and in Pakistan and India. In India, it was seen in the dry areas in Rajasthan, Gujarat, Madhya Pradesh, Andhra Pradesh, Maharashtra, Tamil Nadu, and Karnataka
=About 50 million people were estimated to be infected with the worm.
=The infection has been eradicated from India and all of south-east Asia region by 2000.
=The disease still remains endemic in 13 African countries including Sudan (highest incidence), Niger, etc.
Development of Larvae in Cyclops
=The larvae swim about in water, where they survive for about a week.
=They are swallowed by the fresh water copepod cyclops, which is the intermediate host
=The larvae penetrate the gut wall of the cyclops and enter its body cavity, where they moult twice.
=In about 2–4 weeks, they develop into the infective third-stage larvae (L3).
=The entire life cycle takes about a year, so that all the infected persons develop the blisters and present with clinical manifestations.
Morphology of Dracunculus medinensis
=Adult Worm The adult female is a long, cylindrical worm with smooth milky-white cuticle resembling a long piece of white twine.
*It has a blunt anterior end and a tapering recurved tail.
*It measures about a meter (60–120 cm) in length and 1–2 mm in thickness.
*The body of the gravid female is virtualy filled with the branches of an enormous uterus, containing some 3 million embryos.
*The female worm is viviparous.
=The male worm, which is rarely seen, is much smaller than female being 10–40 mm long and 0.4 mm thick.
*Female worm survives for about an year, whereas life span of male worm is not more than 6 months.
=Larva
*The larva measures 500–750 µm in length and 15–25 µm in breadth.
*It has a broad anterior end and a slender filiform tail which extends for a third of the entire body length
*The cuticle shows prominent striations.
*The larva swims about with a coiling and uncoiling motion.
Life Cycle of Dracunculus medinensis
=D. medinensis passes its life cycle in two hosts.
*Definitive host: Man
*Intermediate host: Cyclops, in which embryos undergo developmental changes.
*There is no animal reservoir.
=Infective form: Third-stage larva present in the hemocele of infected cyclops.
=Mode of transmission: Humans get infected by drinking unfiltered water containing infected cyclops.
=Incubation period: About 1 year.
=The adult worm, which is viviparous discharges larvae, which are ingested by the fresh water crustacean Cyclops, the intermediate host.
Development of Adult Worm in Man
=When water containing infected cyclops is swallowed by man, the cyclops is killed by the gastric acidity and the guinea worm larvae present in its hemocele are released.
=The larvae penetrate the wall of the duodenum and reach the retroperitoneal and subcutaneous connective tissues.
=Here, the larvae develop into male and female adults in about 3–4 months and mate.
=After mating, the male worms die in the tissues and sometimes become calcified.
=In another 6 months time, the fertilized female worm grows in size, matures, and migrates within the connective tissues throughout the body, to finally reach a site where it is likely to come into contact with water.
=The most common site involved is the leg, but other sites such as arms, shoulder, breast, buttocks, or genitalia may also be affected.
=At this site, it secretes a toxin that causes a blister formation, which eventually ruptures, discharging a milky-white fluid containing numerous L1 stage larvae.
=This process continues for 2–3 weeks, till all the larvae are released.
Pathogenicity and Clinical Features
=D. medinensis causes dracunculiasis or dracunculosis.
=Infection induces no illness till the gravid female worm comes to lie under the skin, ready to discharge its embryos.
=The body fluid of the adult worm is toxic and leads to blister formation.
=A few hours before the development of the blister, there may be constitutional symptoms such as nausea, vomiting, intense pruritus, and urticarial rash.
=The blister develops initially as a reddish papule with a vesicular center and surrounding induration.
=The most common sites for blister formation are the feet between the metatarsal bones or on the ankles.
=The fluid in the blister is a sterile yellowish liquid with polymorphs, eosinophils, and mononuclear cells.
=The local discomfort diminishes with the release of the embryos.
=Secondary bacterial infection is frequent. Sometimes, it may lead to tetanus.
=Sometimes, the worm travels to unusual sites such as the pericardium, the spinal canal, or the eyes, with serious effects.
=Dracunculiasis lasts usually for 1–3 months.
Laboratory Diagnosis
=Detection of adult worm: Diagnosis is evident when the tip of the worm projects from the base of the ulcer. Calcified worms can be seen by radiography.
=Detection of larva: By bathing the ulcer with water, the worm can be induced to release the embryos, which can be examined under the microscope.
=Skin test: An intradermal test with guinea worm antigen elicits positive response.
=Serological test: Enzyme-linked immunosorbent assay (ELISA) and immunofluorescence assay (IFA) are frequently used to detected antibodies to D. medinensis
Prophylaxis
=Provision of protected piped water supply is the best method of prevention or else Boiling or filtering water through a cloth and then consuming water.
=Destroying cyclops in water by chemical treatment with Abate (temephos).
=Not allowing infected persons to bathe or wade in sources of drinking water.
Note: Because of its simple life cycle, localized distribution, and the absence of animal reservoirs, guinea worm infection was eradicable. Measures to eliminate the infection have been successful. Global eradication of the infection is imminent.
Treatment
=Antihistaminics and steroids are of help in the initial stage of allergic reaction.
=Metronidazole, niridazole, and thiabendazole are useful in treatment.
=For removal of the worm, the best method is the ancient technique of patiently twisting it around a stick. It may take 15-20 days to extract the whole worm but if care is taken not to snap the worm, this method is safe and effective.
=Surgical removal of the worm under anaesthesia is another method of treatment
