AJTMH Transactions of the Royal Society of Tropical Medicine and Hygiene
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Am. J. Trop. Med. Hyg., 5(6), 1956, pp. 1000-1009
Copyright © 1956 by The American Society of Tropical Medicine and Hygiene

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Experimental Entamoeba Histolytica Infections in Man1

Paul C. Beaver, Rodney C. Jung, Harry J. Sherman, Thomas R. Read AND Thomas A. Robinson2
Department of Tropical Medicine and Public Health, Tulane University School of Medicins, New Orleans, Louisiana, and Medical Department, Mississippi State Penitentiary, Parchman, Mississippi

Eighty-one experimental Entamoeba histolytica infections were studied in human volunteers at a state penitentiary. Inoculation of 2,000 to 4,000 cysts derived directly from a non-symptomatic "carrier" or after one or two passages through volunteers, produced infections in 42 of 42 individuals not medicated or previously infected; heavier inocula did so in 4 of 4 others.

Prepatent periods, based on zinc sulfate flotation and saline smear fecal examinations, varied from 2 days to 4 months. In all but 2 of 48 individuals the stools were positive within 2 weeks; 68.7 per cent were positive in 7 days or less. An extraordinarily long prepatency of 4 months in one case was associated with abnormally pale, mucoid stools.

From 33 individuals followed for more than 1 month after infection, 86 per cent of the stools examined were positive. In one there were 3 periods of 4 to 7 weeks when amebae could not be demonstrated. Among 23 infected individuals observed for 9 to 14 months there were 7 who apparently lost their infections spontaneously after 3 weeks to 8 months. One of 3 individuals who had spontaneously lost infections was refractory to reinfection when given two inoculations of 4,000 cysts.

None of the volunteers developed symptoms that could be associated with the amebic infections. However, the strain of amebae used in the human experiments could not be regarded as non-pathogenic, since it produced typical amebic lesions in dogs, guinea pigs and rats, and was as pathogenic in guinea pigs and rats as a recently isolated strain from a frankly dysenteric patient.


1 Supported in part by the USAF under contract AF 18(600)-616, monitored by the USAF School of Aviation Medicine, Randolph Field, Texas.

Presented, in part, at the third annual meeting of the American Society of Tropical Medicine and Hygiene, Memphis, Tennessee, November 4, 1954.


2 Address Medical Dept., State Penitentiary, Parchman, Miss.




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C. A. Hoare
Public Health Hazards of Amoebiasis in the Light of Its Host-Parasite Relations
The Journal of the Royal Society for the Promotion of Health, January 1, 1958; 78(5): 681 - 696.
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Copyright © 1956 by the American Society of Tropical Medicine and Hygiene.