We report the molecular and epidemiological characterization of 128 human T cell lymphotropic virus type 1 (HTLV-1) isolates from Brazilian patients with different clinical manifestations of the infection. Thirty-two percent of the patients were asymptomatic, 44% had HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), and 23% had adult T cell leukemia/lymphoma (ATLL). Phylogenetic analysis performed using part of the LTR region of the viral genome revealed that all Brazilian isolates belonged to the Cosmopolitan subtype, with the following distribution within the Transcontinental subgroup: 81.6% within the Latin American cluster and 15.8% outside the Latin American cluster. Two isolates belonged to the Japanese subgroup. Molecular analysis of the tax region showed a high nucleotide similarity ( approximately 99%) with 41 prototype sequences, including the ATK-1 isolate. The mean number of nucleotide substitutions ranged from 1 to 8. Five specific nucleotide substitutions, C7401T, T7914C, C7920T, C7982T, and G8231A, were highly conserved among the Brazilian isolates (79.6%), with a frequency ranging from 81.6% to 100% in the sample group and from 18.4% to 24.1% in the prototypes used, suggesting the existence of a molecular signature. These changes were not correlated with a specific clinical status of the patients and could be a molecular characteristic of the HTLV-1 strains that circulate in Brazil.

The use of an indirect fluorescent antibody test (IFAT) performed in a "sandwich" technique has demonstrated: (i) the usefulness of the test for the diagnosis of Trypanosoma cruzi infection in the opossum Didelphis marsupialis; (ii) the existence of differences in the serological response of the opossum, that were related to the parasite strain and were clearly evident during the follow-up of experimental infections in laboratory born specimens; (iii) that, despite a good correlation between serological and parasitological examinations, IFAT was the most sensitive diagnostic test used, followed by xenodiagnosis; and, (iv) that in general, the opossum D. marsupialis seems to be a good responder to T. cruzi antigens.

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The spontaneous proliferation of peripheral blood mononuclear cells (PBMCs) is a hallmark of the human T-lymphotropic virus (HTLV) type-1. Cell proliferation is usually measured using a [3H]thymidine incorporation assay. This study aims to quantify the spontaneous proliferation of PBMCs using flow cytometry. PBMCs were cultured for 24 to 120 hours in the presence of 5,6-carboxyfluorescein diacetate succinimidyl ester (CFSE). For comparison, PBMCs were also cultured with [3H]thymidine. The cutoff values for spontaneous proliferation were >0.06 for the division index and >5.8% for the percentage of divided cells. Sixty-two percent of HTLV-1-infected individuals presented spontaneous proliferation of PBMCs, which was detected in the first 24 hours. Moreover, proliferation was detected in CD4+ and CD8+ T-lymphocyte subsets. A positive correlation was found between the division index and [3H]thymidine incorporation. This method may prove useful to better understand the phenomenon of spontaneous proliferation of PBMC of patients infected with HTLV-1.