HTLV-1 has three main routes of transmission. Vertical transmission is most common, through which an infected mother transmits the<unk>  to her child. Interestingly, the risk to a fetus while inside the womb is minimal, given the virtual absence of viral particles in human plasma. Most vertical infection occurs through breastfeeding. About 25% of infants who are breastfed by infected mothers are infected, while less than 5% of children born to but not breastfed by infected mothers are infected. Sexual transmission is second-most common, whereby an individual infects another through exchange of bodily fluids. Some evidence has suggested that male-to-female transmission is more efficient than female-to-male transmission. For example, one study in Japan found a 61% transmission rate for males to females vs. a less than<unk> % rate for females to males. Least common is parenteral transmission through blood transfusion, with an infection rate of 44-63% estimated in one study, and needle sharing among intravenous drug users. With proper prophylaxis (e.g. breastfeeding counseling for mothers, condom use, and donor blood screening), rates of transmission can be effectively reduced. The importance of the various routes of transmission is believed to vary geographically. The research in discordant couples showed that probability of sexual transmission is about 0.9 per<unk> 00 person-years. * In Japan, the geographic clustering of infections suggest that the<unk>  is more dependent on mother-to-child transmission. * In the Caribbean, the geographic distribution of the<unk>  is more uniform, and it is more common among those with many sexual partners, indicating that sexual transmission is more common.
Human T-lymphotropic virus 1
Human T-lymphotropic virus 2
Kaposi's sarcoma-associated herpesvirus
Human herpesvirus 6
Trichodysplasia spinulosa polyomavirus
Human betaherpesvirus 7
Human betaherpesvirus 5
Oncolytic adenovirus