A U.S. isolate of Theileria orientalis, Ikeda genotype, is transmitted to cattle by the invasive Asian longhorned tick, Haemaphysalis longicornis

Authors: DINKEL, KELCEY - Washington State University; Herndon, David; Noh, Susan; LAHMERS, KEVIN - Virginia-Maryland Regional College Of Veterinary Medicine (VMRCVM); TODD, MICHELLE - Virginia-Maryland Regional College Of Veterinary Medicine (VMRCVM); Ueti, Massaro; Scoles, Glen; Mason, Kathleen; Fry, Lindsay

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2021
Publication Date: 3/16/2021
Publication URL: https://handle.nal.usda.gov/10113/7311330
Citation: Dinkel, K.D., Herndon, D.R., Noh, S.M., Lahmers, K.K., Todd, M.S., Ueti, M.W., Scoles, G.A., Mason, K.L., Fry, L.M. 2021. A U.S. isolate of Theileria orientalis, Ikeda genotype, is transmitted to cattle by the invasive Asian longhorned tick, Haemaphysalis longicornis. Parasites & Vectors. 14. Article 157. https://doi.org/10.1186/s13071-021-04659-9.
DOI: https://doi.org/10.1186/s13071-021-04659-9

Interpretive Summary: Recent introduction into the U.S. of both the Asian longhorned tick (Haemaphysalis longicornis) tick and the Apicomplexan parasite Theileria orientalis (Ikeda strain) presents a significant threat to the U.S. cattle industry. Transmission of T. orientalis by this tick species has been demonstrated in other regions of the world and has resulted in severe economic burden. These experiments were performed in order to test the ability of H. longicornis ticks found in the U.S. to transmit T. orientalis also present in the U.S. Results from this work indicate that H. longicornis nymphs were able to acquire T. orientalis from an infected calf, molt to adults and subsequently transmit this parasite to naive calves. These results provide valuable information for the U.S. cattle industry and reinforce the need for continued surveillance and enhanced control measures.

Technical Abstract: Theileria orientalis is a tick-borne hemoparasite that causes anemia, ill thrift, and death in cattle globally. The Ikeda strain of T. orientalis is more virulent than other strains, leading to severe clinical signs and death in less than 5% of affected animals. Within the Asia-Pacific region, where it affects 25% of Australian cattle, T. orientalis Ikeda has a significant economic impact on the cattle industry. In 2017, T. orientalis Ikeda was detected in a cattle herd in Albermarle County, Virginia, United States. Months earlier, the U.S. was alerted to the invasion of the Asian longhorned tick, Haemaphysalis longicornis, throughout the eastern U.S. Abundant H. longicornis ticks were identified on cattle in the T. orientalis-affected herd in VA, and a subset of ticks from the environment were PCR-positive for T. orientalis Ikeda. A strain of T. orientalis from a previous U.S. outbreak was not transmissible by H. longicornis; however, H. longicornis is the primary tick vector of T. orientalis Ikeda in other regions of the world. Thus, the objective of this study was to determine whether invasive H. longicornis ticks in the U.S. are competent vectors of T. orientalis Ikeda. After acquisition feeding on a VA-T. orientalis Ikeda-infected calf as nymphs, a subset of molted adult female tick salivary glands tested positive by PCR for T. orientalis Ikeda. Adult ticks from the same cohort successfully transmitted T. orientalis Ikeda to 3/3 naïve calves, each of which developed parasitemia reaching 0.4-0.9%. Our findings demonstrate that U.S. H. longicornis ticks are a competent vector of the VA-U.S.-T. orientalis Ikeda strain. This data provides necessary information for the U.S. cattle industry regarding the potential spread of this parasite and the necessity of enhanced surveillance and control measures.