Background: Infection with HTLV-I is etiologically linked with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). However some patients with chronic progressive paraparesis resembling HAM/TSP have been shown to be infected with HTLV-II. Objective: To clarify the role of each of these human retroviruses in the etiology of HAM/TSP in Sao Paulo, Brazil. Study design: A detailed serological and molecular analysis of HTLV-I/II infection was performed in a cohort of 19 patients with HAM/TSP attending a neurological clinic. Results: Plasma samples analyzed for anti-HTLV-I/II antibodies using a Western blot assay, comprising HTLV-I (rgp46I)- and HTLV-II (rgp46II)-specific recombinant env epitopes, demonstrated reactivity to rgp46I and hence were typed as seropositive for HTLV-I. Presence of HTLV genomic sequences in peripheral blood mononuclear cells (PBMC) was sought after by PCR using consensus primers SK 110 and SK 111 for the pol region of HTLV proviral DNA followed by hybridization with type-specific probes—SK 112 (HTLV-I) and SK 188 (HTLV-II). Southern blots from all individuals hybridized with SK 112 but not with SK 188, further confirming HTLV-I infection. Cocultivation of PBMC from eight of these patients with activated lymphocytes from normal individuals resulted in active viral production, detected as presence of soluble p24gag antigen in culture supernatants. Investigation of risk factors for HTLV-I infection in these individuals revealed that five out of 19 patients studied (26.3%) had received blood transfusions previous to disease onset. Conclusions: We demonstrate HTLV-I as the only viral type involved in the etiology of HAM/TSP in a cohort from Sao Paulo, Brazil, and emphasize that prevention measures, including widespread routine screening of blood donations for HTLV should be conducted in Brazil.
