A severely swollen knee due to an infection caused by the subcutaneous emergence of an adult female guinea worm (Dracunculus medinensis). 10 to 14 months earlier, this child had unintentionally ingested a copepod, i.e., a water flea that was a larval host from a locally contaminated water source. As part of the guinea worm parasite life cycle, copepods are carriers of the parasitic larvae, and their ingestion leads to one becoming infected with Guinea worm disease (GWD). Once inside the body, the stomach acid digests the water flea, but not the Guinea worm. These larvae find their way to the small intestine, where they penetrate the wall of the intestine and pass into the body cavity. The female Guinea worm grows to a full size adult 60-100 centimeters (2-3 feet) long, and as wide as a cooked spaghetti noodle. She then migrates to the site where she will emerge, usually from the lower limbs, as was the case here. A blister develops on the skin at the site where the worm will emerge. This blister causes a very painful burning sensation and it will eventually (within 24-72 hours) rupture. For relief, people immerse the affected limb in water. When someone with a guinea worm ulcer enters the water, the adult female releases a milky white liquid containing millions of immature larvae into the water, thereby contaminating the water supply. For several days after it has emerged from the ulcer, the female guinea worm is capable of releasing more larvae whenever it comes into contact with water.
