Academic Reading — Test 38

Reading passage

Guinea worm disease, known to scientists as dracunculiasis, is a parasitic infection that has afflicted human populations for thousands of years. References to a "fiery serpent" emerging from the flesh appear in ancient texts, and calcified worms have been recovered from Egyptian mummies. For most of recorded history the disease was simply endured, since no medicine could prevent or cure it. In recent decades, however, a coordinated international campaign has brought the parasite to the edge of extinction, making it a strong candidate to become only the second human disease, after smallpox, to be deliberately eliminated from the planet. The biology of the parasite explains both why the disease is so distressing and why, paradoxically, it can be defeated without drugs or a vaccine. The causative organism is a roundworm called Dracunculus medinensis. Infection begins when a person drinks stagnant water containing tiny crustaceans called copepods, sometimes referred to as water fleas. These copepods harbour the immature larvae of the worm. Once swallowed, the copepods are dissolved by stomach acid, releasing the larvae, which then penetrate the wall of the intestine and migrate into the body cavity. There the worms mature and mate. The male worm dies shortly afterwards, but the female continues to grow over the following months, eventually reaching a length of up to one metre while remaining no thicker than a strand of spaghetti. Roughly a year after the initial infection, the mature female worm moves towards the surface of the body, most commonly in the lower leg or foot. A painful blister forms on the skin, and the burning sensation it produces drives the sufferer to seek relief by immersing the affected limb in cool water. This response is precisely what the parasite requires. On contact with water the blister ruptures and the worm discharges a milky fluid containing hundreds of thousands of larvae. These larvae are eaten by copepods in the water, and the cycle begins again. Because the parasite depends entirely on this sequence of events, breaking any single link in the chain halts transmission completely. The traditional method of removal has changed little over centuries and remains the only practical treatment. The protruding end of the worm is wound a few centimetres at a time around a small stick or piece of gauze, a process repeated daily over a period that may last several weeks. The worm must not be pulled too hard, for if it snaps the remaining portion can retract into the tissue and cause severe inflammation. During this slow extraction the victim is frequently unable to walk or work, which is why outbreaks tend to strike hardest during the planting and harvesting seasons, deepening the poverty of already vulnerable rural communities. The eradication programme, launched in the mid-1980s and led by a former United States president through his foundation, deliberately avoided high-technology solutions in favour of simple, locally sustainable measures. Villagers were taught to filter their drinking water through finely woven cloth, which traps the copepods and renders the water safe. A chemical called temephos was applied to ponds to kill the copepods directly. Above all, communities learned to keep anyone with an emerging worm away from water sources, so that larvae could not be released. Health workers known as village volunteers were trained to recognise cases, report them quickly and supervise containment. The strategy relied on persuading people to change long-standing habits, an effort that demanded patience and trust rather than expensive equipment. The results have been remarkable. In the mid-1980s an estimated 3.5 million cases occurred each year across some twenty countries in Africa and Asia. By recent years that figure had fallen to fewer than twenty human cases annually, confined to a handful of countries in sub-Saharan Africa. Yet the final stage of eradication has proved unexpectedly stubborn. A growing number of infections have been detected in domestic dogs, which can carry the same parasite, complicating the picture because the campaign was originally designed around human behaviour alone. Insecurity and armed conflict in some remaining regions also hinder the surveillance that certification of eradication demands. Officials insist that the goal remains achievable, but caution that the last few cases are often the hardest and most costly to find. Should the campaign succeed, it will stand as proof that a devastating disease can be conquered through education and persistence rather than medicine.