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Epidemiology and Pathology

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Fig. 27.2 A,B. Life cycle of D. medinensis.

Transmission of the disease occurs through contamination of water with free-swimming larvae of D. medinensis. These emerge from the ruptured uterus of mature female worms lying in the skin and subcutaneous tissues of infected individuals while they bathe in, or gather water from, shallow ponds, step-wells, or cisterns (Fig. 27.2). Thus, the disease prevails in rural areas where there is little sanitary control over the sources of water for the villagers. In times past, in hyperendemic regions, such as Madras and Deccan Provinces in India and in several areas of West and Central Africa, the prevalence reached 85% of those over age 30.

Unfortunately, in some rural areas where agriculture is the mainstay of the economy and survival, the peak incidence of dracunculiasis often occurs during the time crops are sown or cultivated. The disease, therefore, considerably impacts not only the individual but the entire community, since 30-40% of farm laborers may be infected and disabled for as long as 3 months; in affected villages, agricultural production falls by about 30%. A recent study in Sudan showed that children whose parents had dracunculiasis in one year were twice as likely to have malnutrition the next year. Also, their education is imperiled since infected children cannot walk to school, and many others drop out of school to take over their disabled parent's chores.

The larvae liberated from female worms enter fresh water and are infective for 5-6 days; they must be ingested by a minute crustacean (cyclops) within this time period for further development to occur. First stage larvae undergo two molts within the cyclops and develop into third stage infective larvae ( average size 450 x 14 Ám) in about 2 weeks. After the 4th week, the larva does not change, but may remain alive for over 40 days in the cyclops; if the cyclops dies, the embryo also perishes.

Humans are infected when the infected cyclops are swallowed by people who obtain drinking water from shallow ponds, wells or cisterns, especially in the dry season when the surface water is low and the cyclops are concentrated in a smaller volume of water. Dracunculiasis is most common in areas with extended dry seasons. In savannah areas where ponds dry up during the dry season, dracunculiasis is seen only during the rainy season.

When a cyclops containing an infective larva of Dracunculus is swallowed in drinking water, it is killed by the hydrochloric acid in the gastric juice; the larva breaks out of the dead cyclops and penetrates the human duodenal mucosa to eventually reach the connective tissues, where it develops into a mature worm. Copulation and fertilization of the young female worm takes place in the subcutaneous tissues where mating occurs about 3 months after the initial infection. The females then burrow into the deeper connective tissues, assuming a coiled posture in the retroperitoneum or pelvis, or adjacent to long bones or joints of the extremities. They remain in these locations until the branched uterus becomes distended with developing larvae. Most of the female worms reach the lower extremities 8 to 10 months after infection.

The adult male guinea worm is only 1.2-4 cm long, whereas the slender female worm may reach great lengths of 30 to 120 cm (1 to 4 feet) (Fig. 27.3). Most commonly its length ranges from 18 to 30 inches, with a thickness of 1.5 to 2 mm. The male worm probably dies after copulation and may calcify within the tissues, but it is rarely seen.

Fig. 27.3 A,B Adult D. medinensis worms.A The adult female guinea worm is a long, slender worm ranging from 30 to 120 cm in length and from 0.09 to 0.17 cm in width. AFIP N-81415. B Three mature guinea worms removed from the subcutaneous tissues of raccoons. Note the tiny size of the mature male (mm) compared with the mature female (mf) and especially the markedly elongated and serpiginous, gravid female worm (gf). The gravid female shows an extruded uterus (eu). AFIP 68-5166.

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