Theileria
Theileria orientalis Ikeda in North America
Theileria orientalis is a haemoparasite of cattle, spread by the invasive Longhorned Tick, Haemaphysalis longicornis.1 While benign strains of T. orientalis are endemic in the United States, the most virulent genotype, Ikeda, first emerged in North America in 2017 in Virginia.2 While many cases are asymptomatic, clinical infections can result in anemia, ill thrift, jaundice, abortion, and death in serious cases, with recovered animals becoming persistent carriers.3 Additional production losses in both beef and dairy have been observed in association with Ikeda infection.4,5 With no effective vaccine or treatment available in the United States, surveillance testing is crucial for management to avoid introducing naïve animals into endemic areas.6 ViTALS has led molecular assay development and surveillance efforts in the Eastern and Midwestern United States since it’s the initial 2017 detection, and continues to provide crucial services to further surveillance and research efforts into Ikeda in North American cattle (see list of ViTALS-associated research below).
Oakes et al., 2019 https://pmc.ncbi.nlm.nih.gov/articles/PMC6711211/
Thompson et al., 2020 https://www.sciencedirect.com/science/article/abs/pii/S1877959X20301072
Dinkel et al., 2021 https://link.springer.com/article/10.1186/s13071-021-04659-9
Oakes et al., 2022 https://journals.sagepub.com/doi/full/10.1177/10406387211057627
Telionis et al., 2022 https://www.mdpi.com/2076-0817/11/11/1353
Warasi et al., 2022 https://link.springer.com/article/10.1007/s13253-022-00511-4
Guynn et al., 2024 https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2024.1432228/full
Burgess et al., 2024., https://journals.sagepub.com/doi/full/10.1177/10406387241287516
Maboni et al., 2025 https://www.sciencedirect.com/science/article/pii/S2405939025000875
Burgess et al., 2025 https://papers.ssrn.com/sol3/papers.cfm?abstract_id=5164040
Burgess et al., 2026 https://journals.sagepub.com/doi/full/10.1177/10406387251405762
1. Dinkel, K.D., Herndon, D.R., Noh, S.M., Lahmers, K.K., Todd, S.M., Ueti, M.W., Scoles, G.A., Mason, K.L. and Fry, L.M., 2021. A US isolate of Theileria orientalis, Ikeda genotype, is transmitted to cattle by the invasive Asian longhorned tick, Haemaphysalis longicornis. Parasites & vectors, 14(1), p.157.
2. Oakes, V.J., Yabsley, M.J., Schwartz, D., LeRoith, T., Bissett, C., Broaddus, C., Schlater, J.L., Todd, S.M., Boes, K.M., Brookhart, M. and Lahmers, K.K., 2019. Theileria orientalis Ikeda genotype in cattle, Virginia, USA. Emerging Infectious Diseases, 25(9), p.1653.
3. Watts, J.G., Playford, M.C. and Hickey, K.L., 2016. Theileria orientalis: a review. New Zealand veterinary journal, 64(1), pp.3-9.
4. Emery, D., Wang, S., Loo, C. and Shirley, C., 2021. A longitudinal study of infection with genotypes of Theileria orientalis in calves and introduced cattle at Dorrigo, New South Wales, and the effect on weight gains. Veterinary parasitology, 296, p.109487.
5. Perera, P.K., Gasser, R.B., Firestone, S.M., Anderson, G.A., Malmo, J., Davis, G., Beggs, D.S. and Jabbar, A., 2014. Oriental theileriosis in dairy cows causes a significant milk production loss. Parasites & vectors, 7(1), p.73.
6. Emery, D.L., 2021. Approaches to integrated parasite management (IPM) for Theileria orientalis with an emphasis on immunity. Pathogens, 10(9), p.1153.