Human T-cell leukemia virus type 1 infection among Japanese immigrants and their descendants living in Southeast Brazil: A call for preventive and control responses.

Human T-cell leukemia virus type 1 (HTLV-1) has worldwide distribution and is considered endemic in southwestern Japan. HTLV-1 infection has been associated with adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) besides other diseases. This cross-sectional study aimed to investigate the prevalence, risk factors and molecular characterization of HTLV-1, among the world's largest population of Japanese immigrants and their descendants outside of Japan, in São Paulo, Southeast Brazil, as well as to analyze the phylogenetic relationship among isolates of HTLV-1. From July to December 2017, 2,139 individuals from five Japanese associations were interviewed and submitted to blood collection. All serum samples were first tested for the presence of anti-HTLV-1/2 antibodies by ELISA and then peripheral blood from individuals with positive serological results were analyzed for the presence of HTLV-1 5'LTR proviral DNA. Partial sequencing of the 5'LTR region of HTLV-1 proviral DNA was performed by Sanger. The prevalence of HTLV-1 infection was 5.1% (CI 95%: 4.2-6.0). In the multiple logistic regression model, HTLV-1 infection was associated with age ≥ 45 years, female sex, being first and second-generation Japanese immigrants, and having sexual partners with history of blood transfusion. The phylogenetic analysis revealed that all HTLV-1 were classified as Cosmopolitan (1a) subtype. Of them, 47.8% were classified as Transcontinental (A) subgroup and 52.2% as belonging to the Japanese (B) subgroup. Although most HTLV-1-infected patients were asymptomatic (97.3%), blurred vision was associated with HTLV-1 infection. The high prevalence of HTLV-1 infection found in this studied population and especially the intra- and interfamily HTLV-1 transmission presents an urgent call for preventive and control responses of this infection in Brazil.

HTLV-1 intrafamilial transmission among Japanese immigrants in Brazil.

Human T-lymphotropic virus type 1 (HTLV-1) is the etiological agent of adult T-cell leukemia/lymphoma and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The aim of this study was to investigate the intrafamilial transmission of HTLV-1 among Japanese immigrants and their descendants living in a non-endemic area of central Brazil. Six families were investigated. Thirty-seven relatives of the six index cases were tested by ELISA for the presence of anti-HTLV antibodies, and the positive cases were confirmed by Western blot. HTLV-1 isolates were genotyped by partial nucleotide sequencing (5' LTR) of the proviral DNA. All individuals, including index cases and relatives, were asymptomatic. In five families, at least one relative was infected with HTLV-1. In all, eight (22%) relatives (one mother, four wives, one brother, and two brothers-in-law) were infected. However, none of the 22 individuals under 55 years of age was infected. In each family, the HTLV-1 sequences from the relatives were identical or almost identical to that of the index case, except in one case. Pedigrees of the families, together with socio-demographic data of the HTLV-1 infected individuals, strongly suggested the occurrence of both vertical and sexual transmission, with breastfeeding as an important risk factor. Whether and why the virus transmission is less effective among younger generations deserves to be further investigated.