Immunity to Amebic Infection in Dogs

Abstract

Summary An attempt has been made to assess the degree of resistance to reinfection with Endamoeba histolytica following elimination of previous amebic infection. Inoculation was made by intubation per anum of trophozoites in dysenteric aspirates obtained from infected dogs. The initial induced infection rate of amebiasis in dogs was 85 per cent. Despite repeated attempts to reestablish infections in animals whose initial infection had been terminated, using equivalent or greater inocula, only 17 per cent could be reinfected. This indicates the development of acquired immunity to reinfection with E. histolytica in dogs. The resistance to reinfection in dogs was active against both homologous and heterologous strains of E. histolytica. The strains employed differed distinctly in their culturability. The tested duration of immunity to reinfection ranged from ten weeks to 9½ months. Over the periods observed, no animal lost its resistance to reinfection once it was established following an initial infection. A small series of animals which received pre-inoculation blood transfusions from dogs which had become refractory to reinfection with E. histolytica, thus far has shown a lower infection rate than that of animals which were not transfused. This suggests the possibility of passive transfer of immunity in experimental amebiasis in dogs.