Epi. 299 – Theileria orientalis Ikeda and the Longhorn Tick – Sponsored by Boehringer Ingelheim

AABP Executive Director Dr. Fred Gingrich is joined by Dr. Sierra Guynn, Clinical Associate Professor at the Clemson University College of Veterinary Medicine. Guynn is a recognized expert and researcher on this emerging disease and invasive tick. She also is the chair of the AABP Beef Health Management Committee. 

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The Longhorn tick is the biological vector for Theileria orientalis. The tick is an invasive species, first appearing in West Virginia in 2010 based on retrospective identification, and has spread across a large portion of the US. The tick is parthenogenetic, meaning it can reproduce asexually and produce over 2,500 eggs per day. 

Theileria spp. are eukaryotic protozoans, therefore antibiotics are ineffective. Antiprotozoals are ineffective based on studies in other countries and the medication buparvaquone has been used in other countries to decrease mortality when anemia is severe; however, it will not prevent the carrier state. The meat withhold on buparvaquone is 18 months and milk withhold is 42 days in other countries. 

The acute syndrome results in intravascular hemolysis and clinically is not distinguishable from anaplasmosis in cattle. Guynn discusses the diagnostic criteria for determining if an animal has died or is affected by clinical theileriosis. A positive PCR does not indicate clinical disease due to the lifelong carrier state. Guynn also describes expected morbidity and mortality but cautions that this is highly variable between countries and individual farm operations.