Genomic characteristics of emerging human pathogen Rickettsia aeschlimannii isolated from two Hyalomma tick species

<i>Rickettsia aeschlimannii</i>, which emerged in Morocco in 1997, causes the Mediterranean spotted fever-like rickettsiosis in various Mediterranean countries and recently in Russia and China. Despite its increasing distribution, no available genome has been reported outside Morocco to date. Here, we isolated two strains of <i>R. aeschlimannii</i> from <i>Hyalomma asiaticum</i> (Ning-1 strain) and <i>Hyalomma scupense</i> (Ning-2 strain) ticks in northwestern China and assembled their complete genomes. The genomes of the two strains were smaller than the Mediterranean MC16 strain, containing fewer pseudogenes, higher <i>ralF</i> virulence factor coverage, and 154 unique orthogroups. The Ning-1 strain overwhelmed the Ning-2 strain with more obvious cytopathic effects, quicker growth, and faster plaque formation in cell culture, likely due to its unique <i>pmp20</i> gene, higher frequency of single nucleotide polymorphisms, and missense/silent ratio. The prevalence of <i>R. aeschlimannii</i> was high among <i>Hyalomma</i> ticks in northwestern China. These findings highlight the genomic characteristics of <i>R. aeschlimannii</i> and the necessity for enhanced surveillance of the emerging <i>Rickettsia</i> in the human population.