This study was carried out to compare the infection course of Trypanosoma cruzi in the ACA inbred mouse strain inoculated with 2000 blood trypomastigotes of the Tulahuen strain and the Colombian Munantá strain. Parasitaemia and mortality rates showed different patterns for both strains of the parasite. All the Tulahuen infected mice died within 3 weeks after infection, in contrast, all mice infected with the Munantá strain survived, although they showed higher level of parasitaemia. These results are in agreement with previous findings suggesting poor correlation between death and parasitaemia level. The histopathological study showed different degrees of parasitism and inflammatory infiltrates in the heart, according to the parasite strain. The infection with the Munantá strain resulted in scarce parasitism and discrete inflammatory infiltrate. However, severe inflammation and tissue parasitism were observed in the Tulahuen infected mice. The protective effect of the non virulent Munantá strain against infection with the virulent Tulahuen strain was studied. When the Tulahuen strain was inoculated into mice after a challenge with the Munantá strain, parasitaemia was more controlled, and all the mice survived, showing lower inflammatory infiltration and a low number of pseudocysts. Application of these results to vaccine development is proposed.

En el presente estudio se realizó una comparación en el desarrollo de la infección con 2.000 tripomastigotes, en ratones ACA, usando las cepas Tulahuen y Munantá de Trypanosoma cruzi, aisladas originalmente en Chile y Colombia, respectivamente. La cepa ACA se mostró como altamente susceptible a la infección con la cepa Tulahuen, muriendo el 100% de los animales dentro de las 3 semanas postinfección. Sin embargo, todos los ratones infectados con la cepa Munantá sobrevivieron a pesar de alcanzar mayores niveles de parasitemia. El estudio histopatológico de corazón mostró diferentes grados de parasitismo intracelular e infiltrado inflamatorio en relación con la cepa de parásito utilizada. En la infección con la cepa Munantá se pudo observar escasa presencia de pseudoquistes, en este tejido, con una discreta inflamación. Por el contrario, los tejidos de los animales infectados con la cepa Tulahuen mostraron un alto número de parásitos intracelulares y un severo proceso inflamatorio. Se investigó el posible efecto protector de una primoinfección con la cepa no virulenta Munantá frente a una posterior infección con la cepa virulenta Tulahuen. Los animales reinfectados con esta última cepa mostraron menores niveles de parasitemia, 100% de sobrevivencia y menor daño tisular.

In experimental murine infections with Trypanosoma rangeli it has been observed development immune response to Trypanosoma cruzi. The aim of the present work was to analyze the result of antigenic stimuli and the protective effect with T. rangeli in T. cruzi infections. Mice groups immunized with metacyclic trypomastigotes of T. rangeli (Choachí-2V strain), derived from haemolymph and salivary gland and reinfected with T. cruzi virulent populations (Tulahuen strain, SA strain and Dm28c clone) from infected in vitro cells, showed decrease severity of disease outcomes, low parasitemia levels and 100% survival of all mice immunized, in comparison with groups infected only with T. cruzi populations, which demonstrated tissue affection, high parasitemia levels and the death of all animals. The above mentioned data contribute to understand the biological behaviour of T. cruzi and T. rangeli and their interaction with vertebrate host.

Mice from ACA and A.Sn strains were equally susceptible (100% mortality) to intraperitoneal infection with 2000 blood trypomastigotes from Tulahuen strain of Trypanosoma cruzi, while A.Sw and HTI strains were resistant (100% survival). However mice from A.Sw and HTI strains showed significantly higher level of parasitemia than the susceptible strains. The histopathology of miocardial and skeletal muscle was evaluated in the susceptible and resistant strains of mice. In the first ten days post-infection no significant differences in tissue damage were observed. However in the third week of infection, while A.Sw and HTI mice showed recovery of tissue lessions, the susceptible A.Sn and ACA showed increased tissue damage although no blood forms and intracellular parasites were detected. Serum samples from infected mice were tested by dot-immunoradiometric assay, for reactivity against recombinant antigens 1,2,13,26,30,36 and SAPA of T. cruzi. All mice sera only reacted with clones 13 and SAPA, suggesting that this reactivity seems not to be involved in susceptibility or resistance to infection with Tulahuen strain of T. cruzi

Ratones de las cepas ACA y A.Sn fueron altamente susceptibles, con un 100% de mortalidad alrededor de las 3 semanas postinfección (p.i), con un inóculo por vía intraperitoneal de 2000 tripomastigotes sanguíneos de la cepa Tulahuen de Trypanosoma cruzi, mientras que las cepas A.Sw y HTI se comportaron como resistentes con un 100% de sobrevida, pasados los 6 meses p.i. Sin embargo, los animales de las cepas resistentes mostraron niveles máximos de parasitemia significativamente más altos que las cepas susceptibles. Se realizó un estudio histopatológico de músculo cardíaco y esquelético de los ratones infectados. En los primeros 10 días p.i. no se observaron diferencias claras entre cepas resistentes y susceptibles, en cuanto al daño tisular y presencia de parásitos intracelulares (pseudoquistes). Pero alrededor de la tercera semana p.i. ya se vieron diferencias evidentes, mientras los animales de las cepas A.Sw y HTI mostraron bajos niveles de inflamación y signos de recuperación de las lesiones, los ratones ACA y A.Sn evidenciaron un progresivo aumento del daño tisular, aunque no se observaron, en este momento, formas sanguíneas ni intracelulares del parásito. Muestras de suero de los ratones infectados fueron probados por un ensayo inmunoradiométrico (IRMA), para analizar la reactividad contra los antígenos recombinantes 1,2,13,26,30,36 y SAPA de T. cruzi. Todos los sueros sólo mostraron reconocimiento de las proteínas 13 y SAPA, sugiriendo que esta reactividad no pareciera estar relacionada directamente con el fenómeno de resistencia o susceptibilidad a la infección con la cepa Tulahuen de T. cruzi, en el modelo murino