In their research Francisco Úbeda and Vincent Jansen used epidemiological models to explain why human T-cell Lymphotropic virus Type-1 has a more aggressive progression in Japanese men than women. However, it is important to note that it is equally likely in Caribbean men and women. Initially this article seemed like a profound deviation from traditional virological dogma, as viruses that can cross the placental barrier, or be passed through breast milk from mother to child, are relatively rare. Postulating that viruses “evolved” to be softer on women in order to meet this goal of infecting the fetus or baby seems unlikely given how unsuccessful viruses are at accomplishing this goal. Then again, our understanding of viruses is rather limited, but a healthy skepticism of this type of modeling might be beneficial considering there might be other epidemiological or environmental characteristics at play, that could account for this effect in Japanese people specifically. A better understanding of what causes the observed virulence deviations in men and women is needed, and I would like to know how a virus knows it is infecting male versus female hosts, and how it adapts based on this information before coming to a stronger conclusion.