Laboratory Evidence for Transovarial Transmission of Babesia gibsoni by Haemaphysalis longicornis

Babesia gibsoni is a globally distributed tick-borne apicomplexan parasite that threatens dog health, yet its transmission dynamics in Haemaphysalis longicornis remain incompletely defined. Under controlled laboratory conditions, a Babesia-free parthenogenetic H. longicornis colony was used to evaluate transovarial transmission, transmission competence of the resulting F1 stages, retention of transmission competence after feeding on non-susceptible rabbits, and post-molt transmission after larval or nymphal acquisition feeding. Tick samples from the corresponding experimental lineages were screened by pooled internal transcribed spacer (ITS)-targeted nested PCR at the egg, larval, nymphal, and adult stages. Transmission competence was evaluated by infesting splenectomized recipient dogs with the remaining ticks from the corresponding PCR-screened lineages, followed by PCR and blood-smear monitoring. Ticks from a PCR-positive transovarial F1 lineage transmitted B. gibsoni to recipient dogs at the larval, nymphal, and adult stages. Within the transovarial F1 lineage, transmission competence was retained after one or two developmental-stage feedings on non-susceptible rabbits. In contrast, no evidence of post-molt transmission to recipient dogs was observed after larval or nymphal acquisition feeding. Collectively, these findings provide laboratory evidence for transovarial transmission of B. gibsoni and transmission competence of the resulting F1 larval, nymphal, and adult stages in the tested parthenogenetic H. longicornis colony.