Experimental amoebic infection in guinea-pigs immunized with low grade amoebic infection.

Guinea-pigs were immunzied with a low grade amoebic infection, either intracaecally or intramesenterically. The immunized animals were challenged with a virulent strain of Entamoeba histolytica. Some of the animals, immunized via the intracaecal route were challenged repeatedly. 10 to 30% of immunized animals developed caecal lesions compared with 92.8% of non-immunized animals. The percentage of protection in animals challenged repeatedly was greater than in those challenged once. Neither immunized nor non-immunized guinea-pigs developed hepatic abscesses. It appears that prior low grade infection could lead to resistance to subsequent amoebic challenge.