Miarinjara A(1)(2), Eads DA(3), Bland DM(1), Matchett MR(4), Biggins DE(3), Hinnebusch BJ(1). Author information: (1)Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, NIH, Hamilton, MT, USA. (2)Department of Environmental Sciences, Emory University, Atlanta, GA, USA. (3)U.S. Geological Survey, Fort Collins Science Center, Fort Collins, CO, USA. (4)U.S. Fish and Wildlife Service, Lewistown, MT, USA. Prairie dogs in the western United States experience periodic epizootics of plague, caused by the flea-borne bacterial pathogen Yersinia pestis. An early study indicated that Oropsylla hirsuta (Baker), often the most abundant prairie dog flea vector of plague, seldom transmits Y. pestis by the classic blocked flea mechanism. More recently, an alternative early-phase mode of transmission has been proposed as the driving force behind prairie dog epizootics. In this study, using the same flea infection protocol used previously to evaluate early-phase transmission, we assessed the vector competence of O. hirsuta for both modes of transmission. Proventricular blockage was evident during the first two weeks after infection and transmission during this time was at least as efficient as early-phase transmission 2 d after infection. Thus, both modes of transmission likely contribute to plague epizootics in prairie dogs. Published by Oxford University Press on behalf of Entomological Society of America 2022. DOI: 10.1093/jme/tjac021 PMID: 35380675