approximately 1 million cases of Asian schistosomiasis in China, the Philippines, and Southeast Asia (Fig. 3.1).1 Unlike the soil-transmitted helminths, which are nematodes, the schistosomes are a type of flatworm, also known as a trematode or fluke. As adult worms, schistosomes live in the bloodstream (and are known also as blood flukes), where they release eggs armed with a spine that produce serious disease either in the urinary tract or in the intestine and liver, depending on the particular species of parasite. Humans acquire schistosomiasis by direct contact with the larval stages (known as cercariae) that swim in freshwater. Prior to becoming cercariae, the immature developing and reproducing forms of these parasites spend a part of their life history living in various species of aquatic snails.
Few other infectious diseases have influenced history more than schistosomiasis has. Joshua’s curse and the abandonment of Jericho have been attributed to the disease.2 Schistosomiasis was well known to the ancient Egyptians, and it was a major scourge of Napoleon’s army during its disastrous military campaign in Egypt between 1798 and 1801.2 However, some of the most dramatic examples of the schistosome’s historical impact draw from postrevolutionary China during the second half of the 20th century. Shortly after the Chinese revolution in 1949, Mao Zedong (Mao Tse-tung) began planning a massive amphibious assault to bring Taiwan (then known as Formosa) under Communist control. While undergoing rigorous water training around the eastern tributaries of the Yangtze River, tens of thousands of People’s Liberation Army (PLA) troops were exposed to the infectious cercariae of Schistosoma japonicum, the parasitic larvae that live in the water and are shed by snails living in the wet mud along the riverbanks. Within weeks, tens of thousands of soldiers experienced the early acute phase of schistosomiasis, a condition known as Katayama syndrome, which can last for weeks and is characterized by fever, extreme fatigue, muscle pains, and coughing.3 As a result, the launch of the amphibious attack was delayed just long enough for the U.S. Seventh Fleet to enter the Strait of Formosa and abort a Communist takeover. These events are described in a 1959 Harper’s Magazine article titled “The Blood Fluke That Saved Formosa.”4
Figure 3.1 Distribution of schistosomiasis, worldwide, 2009. (See http://gamapserver.who.int/mapLibrary/Files/Maps/Global_schistosomiasis_2009.png [© 2010 WHO].)
Undoubtedly, the derailment of the PLA by a blood fluke transmitted by a snail made a deep impression on the Chinese Communist Party leadership. Beginning in 1955 on the order of Chairman Mao, a special nine-man committee on schistosomiasis was established and a seven-year plan for the eradication of the disease was launched.5 In 1958, beginning with the Great Leap Forward, millions of peasants were mobilized to the Yangtze River valley, where they drained the marshes and buried the “devil snails” under dirt or, in some cases, removed the snails individually with sticks.6 The quotation in the opening of this chapter is from a 1958 paper written by Wei Wen-po (the second-in-command of the nine-man committee) that appeared in the Chinese Medical Journal under the title “The People’s Boundless Energy during the Current Leap Forward.”7 Later, chemical agents to kill the snails were applied. Such low-technology interventions directed at snail control had an important impact and helped to reduce the overall prevalence of schistosomiasis from 12 million or more cases before the revolution to approximately 1.6 million cases by the mid-1980s.6 Mao himself wrote a poem about these successes entitled “Farewell to the God of Plague.” Today, there is a new concern that the completion of the Three Gorges Dam across the Yangtze River might help to establish new ecological niches for snails to thrive and reproduce, thereby causing a rebound in the number of cases of schistosomiasis, just as other dam projects on the Nile at Aswan and the Senegal and Volta rivers in sub-Saharan Africa have caused massive increases in snail populations and reemergence of the disease.8
In Egypt and elsewhere in East Africa, schistosomiasis has had an equally important historical impact. Schistosome eggs have even been recovered from Egyptian mummies dating from the 20th dynasty, around 1000 BCE.2 During the first half of the 20th century, more than half of the populations in some rural villages of the Nile Delta were infected with either Schistosoma haematobium or Schistosoma mansoni. Both forms of schistosomiasis were considered the scourge of the fellaheen, Egypt’s peasant agricultural laborers.9 It was said that hematuria, the bloody urine that results from S. haematobium infection, was so common among Egyptian children and adolescent boys that it was considered a form of male menstruation.9 The initial efforts to control schistosomiasis in Egypt and in neighboring Sudan (where the Gezira Scheme, one of the world’s largest irrigation projects, is located near the confluence of the Blue Nile and White Nile) were organized by the British, initially through multiple injections of toxic antimony compounds to cure the disease in humans and subsequently through widespread use of molluscicides, snail-destroying chemical agents distributed in the environment.10 During the 1960s, Bayluscide (known generically as niclosamide), a molluscicide developed by Bayer, was widely used but later largely abandoned because of price increases combined with a realization that it caused significant damage to fish and other wildlife. Subsequently, during the 1970s, newly discovered drugs, such as ambilhar and hycanthone, were used in large-scale treatment of schistosomiasis, but they too fell into disuse because of their toxicity and some unexplained deaths.10 Complicating Egypt’s schistosomiasis problem was the fact that many schistosome-infected individuals also contracted hepatitis C when contaminated needles and equipment were used to administer tartar emetic, an older and injectable antiparasitic drug that is now seldom used.10 Patients with schistosome and hepatitis C coinfections often suffered from a severe, progressive form of fibrotic liver disease.10 Finally, during the 1990s, widespread use of the anthelmintic drug praziquantel in a 14-year-long mass drug administration campaign, supported in part by the World Bank and the U.S. Agency for International Development (USAID), reduced the overall prevalence of schistosomiasis in Egypt to less than 10% of the population.10 In China, a 10-year World Bank initiative also supporting mass drug administration of praziquantel has resulted in similar dramatic reductions of schistosomiasis in the Yangtze River valley.10
Table 3.1 The major human schistosomes
Despite the successes in China and Egypt, today schistosomiasis still rivals hookworm infection as the most important helminth infection of humans. Urogenital schistosomiasis caused by S. haematobium is responsible for approximately 63% of the cases worldwide, while an intestinal and hepatic form caused by S. mansoni accounts for another 35% (Table 3.1).11 Less than 1% of the global burden of schistosomiasis results from the Cold War warrior S. japonicum.
