It is a virus that human kind has dragged for a very long time, it is transmited the same way hiv virus is, at one point in time hiv was classified as Htlv3, most of the people infected with type 1 don't develop health issues, the consensus is that 1 in 20 will suffer consequences from the virus, but that usually happens after decades of infection. It can be transfered by a mother to child, through sex, and sharing needles or blood transfusions, organ donors. There are no cases that are known to me... I told only what I theoretically know. But to answer your question sex is one of the ways to transmit the virus...