First report of Theileria orientalis Ikeda genotype associated with disease in cattle, Georgia, USA

Theileria orientalis genotype Ikeda is a tickborne parasite that infects red and white blood cells and causes bovine infectious anemia. The primary tick vector for T. orientalis Ikeda is the longhorned tick (Haemaphysalis longicornis). This tick was first detected in the United States in 2017 and in the state of Georgia in 2021, however, to date, no clinical cases of theileriosis in cattle have been reported in the state of Georgia.

A Highland calf was clinically diagnosed with anemia, marked lethargy, tachycardia, tachypnea, decreased rumen contraction rate, dry and flaking skin, and thin and rough hair coat with areas of alopecia. Blood smear evaluation revealed intraerythrocytic piroplasms. PCR and sequencing of the major piroplasm surface protein (MPSP) gene identified T. orientalis genotype Ikeda 2. Another Highland calf from the same farm also presented intraerythrocytic piroplasms in the blood smear and was positive for T. orientalis, but no clinical signs were observed. Clinical signs resolved with ceftiofur crystalline free acid 6.6 mg/kg and imidocarb dipropionate 3 mg/kg, subcutaneously; however, both animals were still positive for T. orientalis after 7 months of treatment.

This is the first clinical case of Theileria orientalis Ikeda genotype 2 diagnosed in Georgia, USA. This is the furthest south where this invasive pathogen has been identified, representing its fast and expanding range in the USA. The presence of T. orientalis Ikeda in Georgia and other states represents an emerging infectious disease issue with the potential for significant animal health and economic impact.