Human T-Lymphotropic Virus Type II (HTLV-II) is a retrovirus that has shown high genetic stability, and low sequence diversity. This low diversity is thought to arise from HTLV-II’s mechanism of replication. HTLV-II is present in Europe and the Americans mainly among Intravenous drugs users (IDUs) and has been show to be endemic in a number of South American and African tribes. Within the former, needle sharing has been identified as the main mechanism of transmission (horizontal transmission), whereas in the latter, the virus is transmitted from mother to child via breast milk (vertical transmission). Previous authors have identified different rates of HTLV-II evolutionin viruses transferred among IDUs and viruses transferred between mother and child in endemically infected tribes. Here, we test whether HTLV-II evolution is dependent on mechanism of transmission. Using updated global HTLV-II sequences and a flexible Bayesian Markov chain Monte Carlo (MCMC) coalescent approach, our results show clearly, in contrast to published data, that HTLV-II evolves at a constant rate, regardless of mechanism of transmission.
