Circulating Trypanosoma cruzi populations differ from those found in the tissues of the same host during acute experimental infection.

We evaluated the presence and distribution of two Trypanosoma cruzi natural isolates in blood, heart, skeletal muscle, liver, and spleen tissues in the acute phase of the experimental infection (35 days postinfection) in order to determine if the populations present in blood were different to those found in the tissues of the same host. Thirty mice were infected with 50 forms of each isolate or with a combination of them. Presence and molecular characterization of the parasites in the host tissues were determined by specific PCR. Cardiac and skeletal muscle alterations were analyzed by histological studies. T. cruzi variability in the host tissues was analyzed through RFLP studies. Both isolates used consisted of a mixture of two T. cruzi lineages. Specific PCRs were positive for most of the samples from the 3 groups analyzed. Cardiac and skeletal muscle sections from the groups infected with one isolate presented mild to moderate inflammatory infiltrates; the group infected with both isolates showed severe inflammatory infiltrates and the presence of amastigote nests in both tissues. Different parasite populations were found in circulation and in the tissues from the same host. These results are important for patients with high probability of mixed infections in endemic areas and contribute to the knowledge of parasite/host interactions.