PROTECTIVE EFFECT OF EXPOSURE TO NONVIRULENT TRYPANOSOMA-CRUZI CLONESON THE COURSE OF SUBSEQUENT INFECTIONS WITH HIGHLY VIRULENT CLONES INMICE

The protective effect of primary infection with non-virulent Trypanoso ma cruzi clones against subsequent infection with highly virulent clon es mas determined in groups of BALB/c mice. All mice inoculated with t ile highly virulent m3 and m4 clones succumbed in less than or equal t o 16 days. Mice inoculated with the nonvirulent h1 and h2 clones survi ved and were superinfected with the m3 and m4 clones. Low degrees of p arasitaemia were observed in mice challenged with the highly virulent clones. The survival ratios of the superinfected mice were not statist ically different from those seen in mice that received a single inject ion of non-virulent cruzi. Mice given a non-virulent infection and sub sequently challenged with a virulent clone differed from those given o nly a non-virulent infection in showing more frequently an inflammator y infiltrate in the heart, skeletal muscle and intestines. (C) 1997 W. B. Saunders Company Limited.