The Power of Plagues. Irwin W. Sherman
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and 700 million people at risk. Ninety percent of the cases are found in sub-Saharan Africa, resulting in >200,000 deaths annually. S. japonicum is found in Southeast Asia and the western Pacific, as well as China, the Philippines, and Indonesia. S. haematobium and S. mansoni are both found in 43 countries in Africa, but the latter species is also found in the Americas (Brazil, Suriname, Venezuela, and the Caribbean).
People who come to the freshwater pools to work, bathe, drink, wash clothes, and swim may also use the water for elimination of their body wastes. Individuals may be infected and reinfected almost daily as they paddle through the cercaria-infested waters that they have come to use as their outdoor toilets. Schistosomiasis remains one of Africa’s greatest tragedies. The highest incidence occurs in African children. In some instances, technology has expanded the numbers of cases. Indeed, every new irrigation scheme and each new dam may pose a new threat.
The Aswan High Dam of Egypt, begun in 1960 with Soviet financing and engineering and requiring 30,000 Egyptians toiling around the clock, was completed in 1971. The High Dam, by controlling the level of water in Lake Nasser, has brought electricity to many parts of Egypt as well as making four crops per year possible through year-round irrigation, but it has also created conditions favorable for the schistosome-carrying snails. Before High Dam construction there was already perennial irrigation in the Nile Delta and the prevalence of schistosomiasis was 60%, whereas in the 500 miles of river between Cairo and Aswan when there was annual flooding the prevalence was 5%. Some 4 years after the dam was completed, the average prevalence between Cairo and Aswan increased 7-fold (35%; range, 19 to 75%).
Schistosomiasis is generally a disease associated with agriculture, but it has also been a military problem ever since the days of Napoleon. During World War II, when U.S. troops stormed ashore on the Pacific island of Leyte in October 1944, they were unaware that in addition to being attacked by Japanese bullets they were also being invaded by the cercaria of S. japonicum. By January 1945 the first cases were diagnosed, and in the end 1,700 men were put out of action at a cost of 300,000 fighting man-days and $3 million. Five years later, 50,000 Chinese communist soldiers prepared for an invasion of Taiwan, but schistosomiasis became so widespread among the troops that the campaign was abandoned and the island was retained by Chiang Kai-Shek’s forces.
Where did schistosomiasis originate? It probably first occurred in animals living in the rain forests and lakes of East Africa and then spread together with its vector snails along the Nile and out into the Middle East and Asia via the trade routes. (Blood flukes occur in birds and mammals other than humans. Indeed, “swimmer’s itch,” or cercarial dermatitis, is found in lakes and along the seashore in Michigan, Minnesota, Wisconsin, New Jersey, and New England, as well as in other parts of the world, and is caused by cercaria [Fig. 3.2G] that normally infect aquatic birds and mammals. The skin rash and pustules are the result of their failure to continue their migration past human skin.)
Snail fever today
Diagnosis of schistosomiasis is made by the examination of stools and urine under the light microscope and the finding of eggs. Sometimes this visual test is supplemented by biopsy and immunologic methods. Preventive measures include education of the population regarding the means for preventing transmission, the treatment of infected persons, and the control of the snail vector using molluscicides. In some cases (e.g., growing rice), avoidance of contact may be impossible. Human exposure can be reduced, however, by the provision of a safe water supply for bathing and washing as well as by the sanitary disposal of human wastes. Other measures may be lining of irrigation channels with cement to discourage snails; intermittent irrigation of rice paddies to disrupt the life cycle; or storage of water away from snails for 2 or 3 days, a time that exceeds the survival time of the miracidia.
The earliest treatment for the disease, developed in 1918, required the intravenous administration of an antimony compound (tartar emetic). In 1929 intramuscular injections of another antimony compound, stibophen, were used, but the cure rates were not as good as with tartar emetic, and both drugs showed severe toxic reactions and sometimes resulted in death. Later, an oral drug, niridazole, was introduced (1964), but it wasn’t until the 1970s that a truly effective drug with low toxicity was developed: praziquantel (trade name: Biltricide). There is no preventative vaccine or drug.
The development of new drugs for the treatment of schistosomiasis can be a long and expensive undertaking. Further, determination of drug efficacy and safety may require extensive animal and human testing. One such heroic effort is worthy of mention. Claude Barlow, an American physician, volunteered for a chemotherapy trial and exposed his abdomen to 224 cercaria, and when cercarial dermatitis developed, he knew he had been infected. He came down with severe schistosomiasis, which required many intravenous injections of tartar emetic for cure. In his old age Barlow wrote: “even today I shudder every time I see a hypodermic needle.”
Today, with hindsight, it is easy to understand why those living in ancient Egypt were unable to control schistosomiasis, but why, 2,000 years later, are we still failing? There are certainly economic constraints such as the cost of pesticides to kill the snails and the cost of drugs, as well as the necessary infrastructure for providing clean water and sanitary disposal of wastes, but in the final analysis it is the habits of the human population that are of critical importance to the elimination of this disease. Since there is no animal reservoir, humans are required for the perpetuation of the disease. As long as infected individuals continue to urinate and defecate in the same waters where the vector snail lives, and to expose their bare skin, there will be blood fluke disease.
The Plague of Athens
The valleys of the Nile and Tigris-Euphrates spawned the civilizations of Egypt and Mesopotamia. The flat fertile valleys made it easier to subject the populations to a single ruler and to oversee individuals so that each had a prescribed role in the society. As a consequence, there emerged in the Fertile Crescent and Egypt a unified system of kingdoms. The different geography of Greece gave rise to another kind of sociopolitical system. Greece, the southernmost extremity of the Balkan landmass, is composed of limestone mountains separated by deep valleys and is cut almost in two by the narrow Corinthian Gulf. The southwestern peninsula was called Peloponnesia, and the northeastern part was called Attica. East of the mainland are the islands of the Aegean Sea; to the south is Crete. In Greece, because the small populations were separated from one another by mountains and the sea, central control was impossible and individuals were not compelled to become specialists but rather masters in a range of accomplishments of hand and mind. Greece, smaller in area than Florida, was never able to support more than a few million inhabitants, but it has played an enormous role in the history of Western civilization. We see some of this today in their monuments, sculptures, paintings, and writings, and we speak of the “glory that was Greece.” Indeed, the prestige of the Greeks in the arts and their ideas on medicine, astronomy, and geography were accepted with unquestioning faith until the 17th century, when a new scientific spirit of experiment and inquiry came into being.
The land and the climate of Greece were unsuitable for farming grains, and as a result, the economy rested on the large-scale movement of goods by ship: the Greeks planted vines and olive trees and produced wine and oil, and these were exchanged for grains and other less valuable commodities. Indeed, an acre of land with vines and olive trees could yield a quantity of wine and oil that could be exchanged for an amount of grain requiring many acres for its production. The outlying communities on the Mediterranean and Black Seas that provided these less valuable commodities were called by the Greeks “barbarians,” from the Greek word barbaros, meaning “foreign” or “uncivilized.” It was the barbarian societies that provided grain, metals, timber, and slaves in exchange for oil and wine and so contributed to the emergence of the Greek civilization.
The Greeks had an unshakable belief in the worth of the individual. While to the east there were absolute monarchies, the Greeks evolved a democratic society where each individual was respected and counted. What developed were states consisting of a city and its surrounding lands whose inhabitants, citizens (literally “those living in the