Little is known of the early history of amebiasis. The disease probably did not become a serious problem until people began to adopt a sedentary, agricultural way of life. Dysentery has been described in the early medical writings of Europe and Asia, and outbreaks were frequent in military units, on slave ships, and in prisons. It is generally impossible, however, to determine whether amebic or bacillary dysentery was involved in any particular outbreak of the "flux."

British doctors in India provided good clinical accounts of amebiasis in the early nineteenth century. In 1828 James Annesley published an important study, based on clinical and pathological work, which clearly linked the intestinal and hepatic aspects of the disease. The pathogen was described in 1875 by a Russian physician, Fedor A. Lösch. Lösch, working in St. Petersburg with a patient from northern Russia, noted the clinical course of the disease, identified the ameba, and was able to produce similar lesions in dogs by feeding them ameba-rich stools from his patient. Lösch, however, believed that something else initially caused the disease and that the ameba merely "sustained" it. Technical problems, especially in identifying amebas and determining which were pathogenic and which were harmless, greatly impeded further research.

Stephanos Kartulis kept interest in the subject alive in the 1880s. Working in Cairo, he established that an ameba was the probable cause of tropical dysentery and managed to transmit infection to kittens. Then in 1890, a Canadian, Henri Lafleur, and an American, William Councilman of Johns Hopkins, published a definitive study of the pathology of the disease. Two German investigators, H. Quincke and E. Roos, distinguished between a pathogenic and a commensal ameba of humans, on clinical and morphological grounds, as well as by infection experiments on kittens. Still, the situation remained confused, as ameba identification and taxonomy was controversial and many research results could not be replicated. Doubts about the significance of pathogenic amebas were widespread in the early 1900s, despite painstaking studies like those of Leonard Rogers in Calcutta. Even Sir Patrick Manson, perhaps the single most important figure in tropical medicine, expressed skepticism about the role of amebas in dysentery as late as 1909. Ernest L. Walker (1913), an American scientist working in the Philippines, established the basic outline of the life cycle of E. histolytica and cleared some of the confusion about nonpathogenic forms with a series of feed ing experiments on volunteer Filipino convicts. The discovery of methods to raise amebas in culture in 1925 has contributed to further clarification. Many mysteries still remain, however, as to distinctions between pathogenic and nonpathogenic strains, and factors such as diet, stress, and concomitant infections that trigger invasiveness in longstanding, asymptomatic infections.

K. David Patterson

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