Testosterone increases the transmission potential of tick-borne parasites

Using laboratory-bred natural rodent hosts that had been castrated and then implanted with either testosterone or inert oil, we have shown that testos terone causes prolonged and more intense infections of a tick-borne piropla sm, Babesia microti. This will result in more ticks becoming infected while feeding. Sexually active male rodents with high testosterone levels are al so known to show increased locomotory activity and reduced innate and acqui red resistance to tick feeding, so that more ticks are likely to be picked up and then fed successfully by these hosts. As a result, the transmission potential of B. microti is significantly increased via hosts with high rath er than low testosterone levels. It is argued that testosterone helps to ge nerate the observed aggregated distributions of parasites amongst their hos ts, which also enhances parasite persistence.