Haemaphysalis longicornis (Acari: Ixodidae) does not transmit Babesia bovis, a causative agent of cattle fever

Authors: Poh, Karen; AGUILAR, MITZI - Washington State University; CAPELLI-PEIXOTO, JANAÍNA - Washington State University; Davis, Sara; Ueti, Massaro

Submitted to: Ticks and Tick Borne Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2024
Publication Date: 7/5/2024
Citation: Poh, K.C., Aguilar, M., Capelli-Peixoto, J., Davis, S.K., Ueti, M.W. 2024. Haemaphysalis longicornis (Acari: Ixodidae) does not transmit Babesia bovis, a causative agent of cattle fever. Ticks and Tick Borne Diseases. 15:(6). https://doi.org/10.1016/j.ttbdis.2024.102374.
DOI: https://doi.org/10.1016/j.ttbdis.2024.102374

Interpretive Summary: Following the recent introduction of the Asian longhorned tick (Haemaphysalis longicornis) into the US, this tick species has been rapidly spreading throughout the country. While the tick is relatively new to the US, Babesia bovis has historically been issue for livestock owners until its eradication from the US in the 1940s. Babesia bovis is the causative agent of bovine babesiosis and may be reintroduced into the US through infected stray cattle that may cross the Texas-Mexico border. Furthermore, the Asian longhorned tick has the potential to invade regions that have historically reported bovine babesiosis prior to its eradication, namely the southeast US. Given this, there is potential overlap between the Asian longhorned tick and B. bovis. Since the Asian longhorned tick can create large populations in a short amount time due to its parthenogenic nature and can potentially overlap with B. bovis in south Texas, it is imperative to understand the role that this tick can play in the bovine babesiosis transmission cycle. The main objective of this study was to establish the vector competency of H. longicornis for B. bovis. This study found that while there is initial evidence of pathogen acquisition by H. longicornis, the tick is ultimately unable to transmit the pathogen to a naïve host through transstadial (pathogen transmission between life stages) or transovarial (pathogen transmission between generations) transmission routes. Therefore, H. longicornis is unlikely to be a vector of B. bovis.

Technical Abstract: The Asian longhorned tick (Haemaphysalis longicornis) was first reported in the US in 2017 and has since been detected in at least 17 states. This tick is known to infest cattle and given its parthenogenic nature, large populations of H. longicornis can lead to significant livestock mortalities and economic losses. While H. longicornis has not been detected in Texas, species distribution models have identified southern Texas as a possible hospitable habitat for this tick. Southern Texas is currently home to the southern cattle tick (Rhipicephalus microplus), which can transmit the causative agent of cattle fever (Babesia bovis). While eradicated from the US, B. bovis has the potential to reemerge in the cattle industry, which could devastate the cattle industry in Texas and much of the southern United States. With the potential for H. longicornis and B. bovis to overlap in southern Texas and their potential to negatively impact the national and global livestock industry, it is imperative to identify the role H. longicornis may play in the cattle fever disease system, if any. A controlled acquisition and transmission experiment tested whether H. longicornis is a competent vector for B. bovis, with the B. bovis-R. microplus system used as a positive control. Transstadial (nymphs to adults) and transovarial (adults to larvae, nymphs, and adults) transmission routes were tested in this experiment. Acquisition nymphs were macerated whole and acquisition adults were dissected to remove midguts and ovaries at five time points (4, 6, 8, 10, and 12 days post-repletion), with 40 ticks processed per time point and life stage. The greatest percentage of B. bovis-positive nymphs occurred 6 days post-repletion (20.0%). For adults, the percent of positive midguts and ovaries increased as days post-repletion progressed, with day 12 having the highest percentage of positive samples (67.5% and 60.0%, respectively). When egg batches were tested in triplicate, all H. longicornis egg batches were negative for B. bovis. During the transmission phase, the subsequent life stages for transstadial (adults) and transovarial transmission (larvae, nymphs, and adults) were fed on naïve, splenectomized calves. All life stages of H. longicornis ticks were negative for B. bovis. Furthermore, the animals were also negative for B. bovis and they did not show signs of bovine babesiosis during the 45-day observation period. Given the lack of successful transstadial or transovarial transmission, it is unlikely that H. longicornis is a competent vector for B. bovis.