Studies on the Pathogenicity of Various Strains of Entamoeba Histolytica after Prolonged Cultivation, with Observations on Strain Differences in the Rats Employed

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Attempts to utilize the rat cecal scoring technique of Neal to measure the invasiveness of strains of Entamoeba histolytica gave inconsistent results when Sherman strain rats were used. Results with Wistar rats were more consistent.

Two strains of E. histolytica, one in culture for 11 years and another in culture for 4 years, were still as highly infective and invasive as were four strains recently isolated from cases of symptomatic amebiasis.

Strain F22 originally isolated from an amebic abscess of the brain showed diminished infectivity and invasiveness. Its infectivity and invasiveness were restored to a level comparable to recently isolated strains when organisms were passed rapidly through rats and culture.

Author Notes

Communicable Disease Center, Public Health Service, U. S. Department of Health, Education, and Welfare, Atlanta, Georgia 30333.