Location: Animal Disease ResearchTitle: Dermacentor variabilis does not transstadially transmit the U.S. Isolate of Theileria orientalis Ikeda: A controlled acquisition and transmission study
|ONZERE, CYNTHIA - Washington State University|
|HASSAN, AMANY - Washington State University|
Submitted to: Parasitologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/2023
Publication Date: 9/14/2023
Citation: Onzere, C.K., Hassan, A., Herndon, D.R., Oyen, K.J., Poh, K.C., Scoles, G.A., Fry, L.M. 2023. Dermacentor variabilis does not transstadially transmit the U.S. Isolate of Theileria orientalis Ikeda: A controlled acquisition and transmission study. Parasitologia. 3(3):284-292. https://doi.org/10.3390/parasitologia3030029.
Interpretive Summary: Since 2017, the potentially virulent Theileria orientalis Ikeda strain has been detected in seven U.S. states and is now endemic in Virginia. As this parasite is primarily transmitted by ticks, establishing knowledge of the vector status for ticks native to the U.S. is a key step in pathogen surveillance and disease monitoring and prevention. In this experiment, we tested the ability of a native U.S. tick species, Dermacentor variabilis, to acquire and transmit the U.S. T. orientalis Ikeda isolate. D. variabilis nymphs were fed on a splenectomized, T. orientalis Ikeda positive calf for parasite acquisition and then allowed to molt to adults. Adult ticks were applied to two, T. orientalis-naïve, splenectomized calves for parasite transmission. T. orientalis was not detected by PCR in the salivary glands of acquisition fed ticks or by PCR and blood smear in the blood of transmission-fed calves. These results suggest that D. variabilis is not a competent vector of the U.S T. orientalis Ikeda isolate.
Technical Abstract: Theileria orientalis Ikeda, an emerging U.S. bovine hemoparasite, causes anemia, abortion, ill-thrift, and occasionally death. While Haemaphysalis longicornis is the primary vector, it is possible that other U.S. ticks are capable of parasite transmission and may contribute to disease spread. Dermacentor variabilis is highly prevalent in the U.S., exhibits a similar geographical distribution to T. orientalis, and is a competent vector of the related parasite, Theileria equi. Herein, we conducted controlled acquisition and transmission studies using splenectomized calves to assess whether D. variabilis can transstadially transmit T. orientalis. D. variabilis nymphs were applied to an infected, splenectomized calf for parasite acquisition and subsequently incubated to molt into adults. Freshly molted adults were applied to two splenectomized T. orientalis-naïve calves to investigate parasite transmission. Calves were monitored for 59 days, and no evidence of parasite transmission was detected using PCR for the T. orientalis Ikeda major piroplasm surface protein gene, blood smear cytology, complete blood counts, or physical examination. Salivary glands from a subset of D. variabilis adults were assessed for T. orientalis using PCR, and the parasite was not detected. These findings support the conclusion that D. variabilis is not capable of transstadial transmission of the U.S. T. orientalis Ikeda isolate.