First finding of <i>Rickettsia rickettsii</i> in <i>Haemaphysalis longicornis</i> (Acari: Ixodidae) in North America

Rocky Mountain spotted fever (RMSF) is a tick-borne infection caused by Rickettsia rickettsii Brumpt, which is included in the spotted fever group (SFG) rickettsioses. In the United States, RMSF is transmitted primarily by ticks in the genus Dermacentor and in parts of Arizona and northern Mexico, by Rhipicephalus sanguineus Latreille. SFG rickettsiosis cases have been reported throughout the United States, but between 2018 and 2022, 5 states (Alabama, Arkansas, Missouri, North Carolina, and Tennessee) accounted for over 50% of SFG rickettsiosis cases. The most virulent of the spotted fever group rickettsia (SFGR), R. rickettsii, is potentially fatal if misdiagnosed or left untreated. Tick surveillance is one tool that public health entomologists utilize in identifying potential hot spots of infected ticks. Although the prevalence of R. rickettsii in tick populations is generally low (∼1% or less), the severity of this disease warrants frequent surveillance for the pathogen. With the inadvertent introduction of the longhorned tick into the United States, and its proven laboratory competence for transmitting R. rickettsii, the New Jersey Department of Health initiated surveillance of this tick for R. rickettsii. Here, we report the first finding of R. rickettsii in field-collected longhorned ticks, Haemaphysalis longicornis Neumann.