Transmission of the agent of human granulocytic ehrlichiosis by Ixodes spinipalpis ticks: Evidence of an enzootic cycle of dual infection with Borrelia burgdorferi in northern Colorado

Previous work described an enzootic cycle of Borrelia burgdorferi sensu lat o (hereafter referred to as B. burgdorferi) maintained by the rodent Neotam a mexicana and the tick Ixodes spinipalpis in northern Colorado, We investi gated the incidence of coinfection among rodents with the agent of human gr anulocytic ehrlichiosis (aoHGE), aoHGE was detected in 23.5% of 119 rodent spleens examined. Biopsy results indicated that 78 (65.5%) of the 119 roden ts were positive for B. burgdorferi, whereas 22 (78.5%) of the 28 animals t hat harbored aoHGE were also infected with B. burgdorferi. In 14 of 25 I. s pinipalpis tick pools, aoHGE was detected by amplifying both the 16s rRNA a nd p44 gene of aoHGE, The ability of I. spinipalpis to transmit aoHGE was e xamined in C3H/HeJ mice. aoHGE was detected in their blood 5 days after I. spinipalpis infestation, This study confirms that both B. burgdorferi and a oHGE can be transmitted by I. spinipalpis ticks and that there is a high in cidence of coinfection in rodents, predominantly Peromyscus maniculatus and N, mexicana, that inhabit the foothills of northern Colorado.