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Following maturation, the female guinea worm migrates to the subcutaneous tissues (Figs. 27.4, 27.5, 27.6, 27.7, 27.8), preferentially seeking out those areas most likely to come in contact with water. Thus, the lower leg, especially over the lateral malleolus of the ankle, is the most frequent site of involvement. Once the female has come to rest in the subcutaneous tissues, she forces her head into the dermis, causing an indurated papule, followed in a few hours by a blister containing turbulent fluid (Figs.27.4 and 27.8). Once the blister contacts water, the guinea worm contracts violently so that the uterus is thrust forward and a loop is extruded. When the blister ruptures, the anterior end of the worm with its prolapsed uterus is exposed to the water. The uterus then ruptures and thousands of tiny larvae (about 64O x 23 µm) with long spine-like tails spill into the water, where they uncoil and swim about, attracting cyclops (water fleas) which soon ingest them. Once the infected limb or other part of the host is removed from the water, the adult worm again withdraws into its tunnel with her uterus protruding for the following 2-6 weeks, only to repeat the process and discharge larvae when the ulcerated blister is again immersed. After the guinea worm has shed most or all her larvae, she dies and is absorbed or becomes necrotic and calcifies in the subcutaneous tissues.

Lesions may develop wherever female worms are present. The anatomical location of the lesions dictates the severity of the host reaction. Although worms can be almost anywhere in the body, they are most common in the subcutaneous tissues, especially of the legs and feet (in over 90% of patients).

Once the cutaneous blister ruptures, a shallow ulcer remains in which the head of the worm may often be seen. There is erythema, edema, and induration surrounding the ulcer and lymphocytes and eosinophils dominate the infiltrate microscopically. There is little inflammatory reaction about the body of the worm while larvae are being discharged to the outside.

After the worm dies, and if there is no secondary infection, healing takes place in 4-6 weeks, during which time the worm is slowly resorbed. There is slight lymphocytic and histiocytic infiltration and foreign body giant cell formation. Usually the worm degenerates within its surrounding abscess (the wall of which consists of granulation or fibrous connective tissue), but part or all of the worm or abscess may calcify. In the subcutaneous tissues calcification is most commonly elongated, string-like, or serpiginous. A whorled pattern of calcification may be seen in coiled, necrotic guinea worms in the muscle planes and soft tissues of the chest, abdomen, retroperitoneum, pelvis, and thighs. Calcified guinea worms have also been noted in the orbit, extradural space, pericardium, scrotum, inguinal lymph nodes, and major joints. Usually there is only a single worm noted in an infected individual per year, but up to 20 worms can appear simultaneously.

If the extruded head and anterior end of the worm is avulsed by trauma or attempted extraction by winding around a stick or by unsuccessful surgical procedure (Figs.27.5A, 27.7C and 27.8), the torn end of the residual worm retracts into the subcutaneous tissues, often bringing bacteria with it along the worm tract to cause a marked cellulitis and abscess with sinuses, discharging pus and worm debris. Dense dystrophic calcification may form around decaying worms which have produced extensive fibrositis, myositis, or abscess formation.

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Fig. 27.4 A-E Various stages in the life cycle of D. medinensis. A There is erythema and swelling over the lateral malleolus of the right ankle (a) of an infected patient, caused by a mature, gravid, female guinea worm beneath the swollen area. This is an earlier lesion than that seen at (b) where a blister has developed, collapsed, and ulcerated. AFIP 67-1563-1. B A close-up view of the same ulcer which has been exposed by surgically opening the blister. A loop of uterus of the adult female Dracunculus protrudes from the base of the ulcer. It is in this manner that the guinea worm sheds thousands of tiny larvae when the affected skin is immersed in fresh water. AFIP 67-1563-5. C Larva of D. medinensis. D Infected cyclops with infective third-stage larvae coiled within its thorax (arrows). x 115. AFIP 68-4630. E Cross section of a gravid female D. medinensis. The body cavity is filled with larvae. X55. (A,B,D courtesy of E. L. Schiller, Baltimore; E from Marty and Andersen 1995.)

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Fig. 27.5 A,B Dracunculus medinensis in the subcutaneous tissues of two African patients. A The female worm is being extracted slowly from the soft tissues over the anterior aspect of the knee. There is surrounding cellulitis and edema from secondary bacterial infection, which can lead to a septic arthritis. B Serpentine outline of a guinea worm beneath the skin over the anterior abdominal wall of a child. (From W.W. Davey: Companion to Surgery in Africa, E & S Livingstone, London, 1968).

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Fig. 27.6 Serpiginous outlines of adult female guinea worms beneath the skin of the knee (A), the flank (B), and below the breast (C) of three different patients. Note in B an ulcerated blister over the head of the worm (right). This raised, cord-like, serpiginous appearance of the guinea worm probably gave rise to the term "plague of the fiery serpents" described by the ancient Israelites.

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Fig. 27.7 A-C Adult female guinea worms in the scrotum. A The raised, cord-like, serpentine outline of an adult worm is seen beneath the skin of the scrotum. B A slender, thread-like guinea worm is partially extruded from the scrotal sac of another patient. C Extraction of adult worms from beneath the scrotal skin by the ancient method of winding the worms around a stick. The protruding portion of the worm is wound around a matchstick or other piece of wood and the stick is turned once or twice a day until the entire worm is extracted. This method is still used today in some countries, but is dangerous because rupture of the worm during the extraction process may spill numerous tiny larvae into the tissues, with secondary bacterial infection, causing violent inflammation, cellulitis, abscess, necrosis and sloughing. Serious disability lasting for weeks or months may ensue, and death from sepsis is possible. Careful surgical dissection and removal of worms under aseptic conditions is recommended.

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Fig. 27.8 A-E Guinea worms protruding from ruptured, ulcerated blisters in their most common locations, the lower leg, ankle and foot. A Multiple worms protrude from ulcerated blisters in the calf and ankle. There is considerable cellulitis and edema. B An adult worm being extracted from an ulcer overlying the ankle. This is the classic method of extraction from ancient times (discussed in the legend to Fig. 27.7). C Guinea worm being extracted with a tweezer from its typical location about the lateral malleolus of the ankle. Note the wide area of cellulitis and edema surrounding the point of exit. D Blister on the foot of a Pakistani just before the worm emerged and E immediately after wetting, showing the blister has ruptured and the female D. medinensis has emerged. (D, E courtesy of Drs. S. Fitzgerald, J. Rippert and Dr. Daniel Connor, from D.H. Connor and F.W. Chandler, eds. Pathology of infectious diseases. Appleton and Lange, Stamford, Conn., 1997).

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