Haemaphysalis longicornis (Acari: Ixodidae) failed to acquire and consequently transmit Babesia bigemina to naïve cattle.

Since its introduction into the United States, the Asian longhorned tick (Haemaphysalis longicornis) has spread to several states and poses a growing threat to livestock due to its broad host range and rapid reproductive capacity. Since H. longicornis can transmit livestock pathogens such as Theileria orientalis Ikeda, it is a high priority to determine the vector competence of a United States population of H. longicornis for other livestock pathogens that circulate or may re-emerge domestically, such as Babesia bigemina, the causative agent of bovine babesiosis. This study evaluated the vector competence of H. longicornis for the acquisition and transmission of B. bigemina, using the Rhipicephalus microplus system as a positive control. Potential transmission routes assessed included transovarial transmission, transstadial maintenance across all life stages, and transstadial transmission from nymphs to adults. Nymphs and adult females were allowed to feed to repletion during acquisition. Twelve days post-repletion, a subset of nymphs were frozen, and adult females were dissected to collect ovaries and midguts. Tick tissues or whole ticks were tested for the presence of B. bigemina using nested PCR (nPCR) followed by quantitative PCR (qPCR). Detectable B. bigemina DNA was observed only in the midguts of adult female ticks following acquisition. During transmission trials, no subsequent life stages or progeny transmitted B. bigemina to naïve calves, as demonstrated by negative nPCR and qPCR results and the absence of clinical signs of bovine babesiosis. Collectively, these findings indicate that H. longicornis does not appear to be a competent vector for B. bigemina.