A U.S. Isolate of Theileria Orientalis, Ikeda Genotype, is Transmitted to Cattle by the Invasive Asian Longhorned Tick, Haemaphysalis Longicornis

Abstract

BACKGROUNDTheileria orientalis is a tick-borne hemoparasite that causes anemia, ill thrift, and death in cattle globally. The Ikeda strain of T. orientalis is more virulent than other strains, leading to severe clinical signs and death in less than 5% of affected animals. Within the Asia-Pacific region, where it affects 25% of Australian cattle, T. orientalis Ikeda has a significant economic impact on the cattle industry. In 2017, T. orientalis Ikeda was detected in a cattle herd in Albermarle County, Virginia, United States. Months earlier, the U.S. was alerted to the invasion of the Asian longhorned tick, Haemaphysalis longicornis, throughout the eastern U.S. Abundant H. longicornis ticks were identified on cattle in the T. orientalis-affected herd in VA, and a subset of ticks from the environment were PCR-positive for T. orientalis Ikeda. A strain of T. orientalis from a previous U.S. outbreak was not transmissible by H. longicornis; however, H. longicornis is the primary tick vector of T. orientalis Ikeda in other regions of the world. Thus, the objective of this study was to determine whether invasive H. longicornis ticks in the U.S. are competent vectors of T. orientalis Ikeda. METHODSNymphal H. longicornis ticks were fed on a splenectomized calf infected with the VA-U.S.-T. orientalis Ikeda strain. After molting, a subset of adult ticks from this cohort were dissected, and salivary glands assayed for T. orientalis Ikeda via qPCR. The remaining adult ticks from the group were allowed to feed on three calves. Calves were subsequently monitored for T. orientalis Ikeda infection via blood smear cytology and PCR.RESULTSAfter acquisition feeding on a VA-U.S.-T. orientalis Ikeda-infected calf as nymphs, a subset of molted adult tick salivary glands tested positive by qPCR for T. orientalis Ikeda. Adult ticks from the same cohort successfully transmitted T. orientalis Ikeda to 3/3 naïve calves, each of which developed parasitemia reaching 0.4-0.9%.CONCLUSIONSOur findings demonstrate that U.S. H. longicornis ticks are competent vectors of the VA-U.S.-T. orientalis Ikeda strain. This data provides important information for the U.S. cattle industry regarding the potential spread of this parasite and the necessity of enhanced surveillance and control measures.

A two-year study on the phenology, host and habitat associations, and pathogens ofHaemaphysalis longicornisin Virginia, U.S.A.

“…However, we continued to detect the pathogen in host-seeking H. longicornis during the 2020 sampling period, further supporting our previous results from 2019 (Thompson et al, 2020b). In addition, recent experimental work has shown that H. longicornis is a competent vector for this pathogen in the United States, warranting continued molecular surveillance for T. orientalis in H. longicornis in other states, especially in regions near cattle operations (Dinkel et al, n.d.). The other apicomplexan detected in H. longicornis was a Hepatozoon sp.…”

Co-Infection of cattle in Virginia withTheileria orientalis ikedagenotype andAnaplasma marginale

“…13 T. orientalis ikeda has recently been identified in cattle in Virginia, affecting animals that were also parasitized with H. longicornis ticks; 10 this tick has been confirmed as a competent vector for the Virginia T. orientalis ikeda . 7 The animals that were clinically affected in this outbreak presented with the typical signs of anemia, icterus, and general malaise. In Virginia, this clinical presentation is identical to the blood infection caused by the bacterium Anaplasma marginale.…”