Can the tick Rhipicephalus microplus transmit Trypanosoma vivax to cattle by the transovarial and mechanical routes?

Abstract

Due to the presence of Trypanosoma vivax DNA in ticks, transovarian and mechanical transmission is suspected. The present study aimed to evaluate (i) the presence of T. vivax in R. microplus that fed on animals with acute trypanosomosis; (ii) the transovarian transmission; and (iii) the ability of larvae and males to mechanically transmit T. vivax to cattle in a region without a cyclic vector. To this end, six calves were experimentally infected with T. vivax on day 0, and after different intervals, these animals were infested with cattle tick larvae. Before oviposition, the content of engorged females was submitted to blood smear to detect trypomastigotes. After oviposition, the engorged females were tested for T. vivax DNA. To assess transovarian transmission, pools of egg masses and larvae from these females were also tested for T. vivax DNA. The larvae were then fed on three negative animals. In addition, to assess mechanical transmission, males from the infestation of animals with trypanosomosis were removed and placed on three other T. vivax-negative calves to feed for 25 days. The male ticks were also tested for T. vivax DNA. The six animals infected with T. vivax showed parasitemia 5-21 days post-infection, when they were treated with a trypanocide drug. Trypanosoma vivax trypomastigotes and DNA were detected in engorged females of R. microplus, but not in egg masses and larvae from engorged females that fed on calves positive for this protozoon. In males, no T. vivax DNA was detected after they fed on cattle positive for T. vivax, and no mechanical transmission was observed.