Epidemiological Description and Molecular Characterization of Intrafamily Transmission of Human T-Lymphotropic Virus Type 1 in an Endemic Region of Brazil

Human T-lymphotropic virus type 1 (HTLV-1) is associated with neurological, degenerative, and inflammatory diseases. Brazil has regions with high prevalence rates. The prevalence among relatives of positive people is high, and intrafamily transmission causes the conservation of the infection for different generations. The investigation of epidemiological and molecular factors may clarify the factors associated with the efficacy of intrafamilial transmission of HTLV-1. Objective: To analyze the epidemiological and molecular factors associated with intrafamilial transmission of HTLV-1 in an endemic area of Brazil. Material and Methods: A cross-sectional study investigated 72 relatives from 14 families with more than one infected. Epidemiological data were collected from all family members, and genetic sequencing was performed, phylogenetic analysis of 22 positive relatives. Results: The prevalence of HTLV-1 in families with infected people was 56.94% (41/72). Twelve vertical transmission routes and ten horizontal transmission routes were identified. Phylogenetic analysis demonstrated the absence of polymorphisms between infected mother and child sequences, while sequences of couples presented nucleotide divergence of up to 3%.among themselves. It was also identified in a family with an intrafamilial transmission with the occurrence of two viral strains. Conclusion: Molecular data confirmed intrafamilial transmission. They also indicated little genetic variability between the sequenced samples of family members and those deposited in GenBank used in this study. The absence of polymorphisms was observed in cases of vertical transmission, indicating a tendency to perpetuate identical sequences regardless of the time of acquisition of the infection.