<i>Babesia microti</i> Transmission Risk Through <i>Ixodes persulcatus</i> Ticks in Selenge, Mongolia, and Investigation of Its Infectivity in Rodents

<i>Babesia microti</i>, a causative agent of human babesiosis, a tick-borne zoonotic disease, has been detected in <i>Ixodes persulcatus</i> ticks in Mongolia. Large-scale surveys of <i>B. microti</i> in ticks and its infectivity in rodents are essential. Of 458 <i>I. persulcatus</i> ticks, 94 females and 176 males were screened for <i>B</i>. <i>microti</i> infection, while 111 female and 77 male ticks were used to investigate <i>B</i>. <i>microti</i> transmission to BALB/c mice and hamsters. The prevalence of <i>B. microti</i> was higher in female ticks (26.6%) than in males (13.1%), with nearly one-sixth (17.8%) of ticks carrying the parasite. The infectivity of Mongolian isolates, as a sister clade to the U.S. lineage, remains unclear, as they failed to infect rodents. Our study suggests that the risk of <i>B</i>. <i>microti</i> transmission is approximately of one-sixth of <i>I. persulcatus</i> ticks, with a higher risk observed in females than in males.