Rickettsia lanei, sp. nov. (Rickettsiales: Rickettsiaceae), a Newly Recognized Pathogen of Humans Associated with the Rabbit Tick, Haemaphysalis leporispalustris (Acari: Ixodidae).

Abstract

Haemaphysalis leporispalustris (the rabbit tick) is one of the most broadly distributed hard tick species in the Americas. In 2018, investigators amplified DNA from a spotted fever group Rickettsia (SFGR) species found in host-seeking larvae and nymphs of H. leporispalustris collected in northern California and proposed the name Candidatus "Rickettsia lanei" using results obtained via multilocus sequence typing. Several years later, other investigators reported the amplification of DNA from the blood of two severely ill patients in northern California that demonstrated near-identical sequences with several gene sequences of Ca. "R. lanei," suggesting that this SFGR is pathogenic to humans. Recently, nearly complete genetic identity was identified between segments of the outer membrane protein A gene of Ca. "R. lanei" and an otherwise unidentified SFGR isolate designated as HLP 7421, which was established in 1961 from H. leporispalustris collected in the Bitterroot Valley of western Montana. Herein, the results of whole-genome sequencing of HLP 7421 are reported, revealing a 1,270,740 base pair chromosome most similar to that of Rickettsia rickettsii subsp. californica, the etiologic agent of Pacific Coast tick fever. Digital DNA-DNA hybridization and orthologous average nucleotide identity percentages between HLP 7421 and several closely related SFGR species meet the criteria for species identification using one genome-based algorithm for defining taxa in the Rickettsia genus. The name Rickettsia lanei is proposed for this pathogen, and its potential contribution to the evolving mosaic of tick-borne spotted fevers in the Americas is discussed.