High Ratio of Human T Cell Lymphotropic Virus Transmission and Prevalence of Human T Cell Lymphotropic Virus Type 1-Associated Diseases in Brazilian Family Groups Followed Up by the GIPH Cohort.

A silent spread of human T cell lymphotropic virus type 1 (HTLV-1) has been occurring for thousands of years, with a high prevalence in some regions due to the sexual and vertical transmission and formation of family clusters. The time from HTLV-1 infection until the onset of virus-associated diseases is extremely long, approximately one to three decades. In this study, we evaluated intrafamilial HTLV-1 transmission and associated diseases in 1,204 individuals enrolled and followed up by the GIPH cohort between 1997 and 2017. The family groups (n = 43) were composed of 279 individuals who were tested for HTLV-1/human T cell lymphotropic virus type 2 (HTLV-2) and were classified as two groups according to the index case: blood donor (blood donors referred to the GIPH cohort) and nondonor (individuals referred to the GIPH cohort by other health services). The observed rates of HTLV-1 transmission and associated diseases among the relatives were high. Of 236 family members and sexual partners tested for HTLV, 104 (44.1%) were confirmed as having HTLV infection, with 36.7% of relatives whose index case was blood donors and 56.9% of relatives with nondonor index cases. At least one case of HTLV-1-associated myelopathy was observed in 42.9% of the families with intrafamilial transmission of HTLV-1. Brazil is an endemic area for HTLV-1/2 and has implemented mandatory universal screening of blood donors for HTLV-1/2 since 1993. However, the lack of public health services offer diagnosis for HTLV to the general population and pregnant women in the country makes it difficult to identify infected people, and contributes to the silent spread of the virus.