Discovery of a novel species Theileria haneyi n. sp. infective to equids highlights exceptional genomic diversity within the genus Theileria: implications for apicomplexan parasite surveillance

Authors: Knowles Jr, Donald; Kappmeyer, Lowell; HANEY, DARRELL - Animal And Plant Health Inspection Service (APHIS); Herndon, David; Fry, Lindsay; MUNRO, JAMES - University Of Maryland; SEARS, KELLY - Washington State University; Ueti, Massaro; WISE, LAUREN - St George'S University; SILVA, MARTA - Washington State University; Schneider, David; GRAUSE, JUANITA - University Of Maryland; White, Stephen; TRENTINA, KYLE - University Of Maryland; BISHOP, RICHARD - Washington State University; ODONGO, DAVID - University Of Nairobi; PELZEL-MCCLUSKE, ANGELA - Animal And Plant Health Inspection Service (APHIS); Scoles, Glen; MEALEY, ROBERT - Washington State University; SILVA, JOANA - University Of Maryland

Submitted to: International Journal for Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2018
Publication Date: 6/6/2018
Citation: Knowles, D.P., Kappmeyer, L.S., Haney, D., Herndon, D.R., Fry, L.M., Munro, J.B., Sears, K., Ueti, M.W., Wise, L.N., Silva, M., Schneider, D.A., Grause, J., White, S.N., Trentina, K., Bishop, R., Odongo, D.O., Pelzel-McCluske, A.M., Scoles, G.A., Mealey, R.H., Silva, J.C. 2018. Discovery of a novel species Theileria haneyi n. sp. infective to equids highlights exceptional genomic diversity within the genus Theileria: implications for apicomplexan parasite surveillance. International Journal for Parasitology. 48(9-10):127-137. https://doi.org/10.1016/j.ijpara.2018.03.010.
DOI: https://doi.org/10.1016/j.ijpara.2018.03.010

Interpretive Summary: These data describe the discovery of a previously undetected exotic parasite in horses. This parasite belongs to a genus that impacts and restricts the international movement of horses. The US and some other countries work to maintain infection free status. The finding of this parasite, designated Theileria haneyi and potential other undetected related parasites will present challenges for global regulatory decision makers.

Technical Abstract: A novel apicomplexan parasite was serendipitously discovered in horses at the United States – Mexico border. Phylogenetic analysis based on 18S rDNA showed the erythrocyte-infective parasite to be related to, but distinct from, Theileria species in Africa, the most similar taxa being Theileria spp. from waterbuck and mountain zebra. The level of divergence at the 18s locus also suggested the likely existence of additional cryptic species. The genome of this novel equid Theileria parasite is most similar to that of T. equi, also a pathogen of horses. However, the predicted divergence time between the new Theileria sp. and T. equi, based on genome sequence data, is greater than 33 million years. Average protein sequence divergence at 23% is greater than that of T. parva and T. annulata proteins which is 18%. The latter represent highly virulent Theileria species of domestic cattle and African and Asian wild buffalo, respectively that differ markedly in pathology, host cell tropism, tick vector and geographical distribution. Despite the overall genomic divergence, the nine member equi merozoite antigen (EMA) superfamily previously unique to T. equi is also present in the novel parasite. As a result of the sequence divergence, this parasite, named T. haneyi to reflect its status as a new species, is not detectable using currently available diagnostic tests. Discovery of this novel species infective to equids highlights exceptional genomic diversity within the genus Theileria and presents implications for apicomplexan parasite surveillance.