Theileria orientalis Ikeda in Cattle, Alabama, USA

SIMPLE SUMMARY: Theileria orientalis Ikeda poses significant challenges to the cattle industry, encompassing economic repercussions, trade-related issues, and constraints regarding control and treatment measures. This parasite can precipitate a range of adverse effects in cattle, including diminished milk production, weight loss, anemia, and, in severe instances, cattle fatalities. These adverse impacts directly translate into economic burdens for farmers and the broader cattle industry. The financial costs associated with treating afflicted animals and implementing control strategies can be substantial. Additionally, occurrences of Theileria orientalis Ikeda in regions where it is not endemic can lead to trade restrictions and impediments affecting both cattle and cattle products. This can curtail the international movement of cattle and influence global trade in livestock. Furthermore, there is a dearth of effective treatment options for infected cattle, and severe cases frequently culminate in fatalities. This lack of viable treatment exacerbates the difficulties in disease management. Addressing the presence of Theileria orientalis Ikeda in the USA necessitates comprehensive efforts to understand the prevalence and distribution of the pathogen. This study utilizing PCR followed by DNA sequencing identified two cases of Theileria orientalis Ikeda-positive cattle, marking the first report of this virulent genotype in Alabama, USA. ABSTRACT: Theileria orientalis Ikeda genotype, a parasite causing a disease in cattle that leads to significant economic challenges in Asia, New Zealand, and Australia, has been identified in seven U.S. States since 2017. Two previously validated PCR tests for Theileria followed by DNA sequencing were performed to test blood samples collected from 219 cattle in Alabama, USA, during the period of 2022–2023. Bidirectional Sanger sequencing revealed that the MPSP gene sequences (639–660 bp) from two cattle in Lee and Mobile Counties of Alabama exhibited a 100% match with those of recognized T. orientalis Ikeda strains, and showed similarities ranging from 76% to 88% with ten other T. orientalis genotypes. A high copy number of T. orientalis Ikeda was detected in the blood of infected cattle (ALP-1: 1.7 × 10(5) and 1.3 × 10(6)/mL whole blood, six months apart; ALP-2: 7.1 × 10(6)/mL whole blood). Although the confirmed competent vector for T. orientalis Ikeda, Haemaphysalis longicornis tick, has not yet been identified in Alabama, the persistent nature of T. orientalis Ikeda infection and the detection of a high pathogen burden in seemingly healthy cattle in this study suggest that other tick species, as well as shared needles and dehorning procedures, could facilitate pathogen transmission within the herd. Continued investigations are necessary for the surveillance of T. orientalis Ikeda and Haemaphysalis longicornis ticks in Alabama and other U.S. states, along with assessing the pathogenicity of T. orientalis Ikeda infections in cattle.