Anaplasma phagocytophilum Variant 1 from White-Tailed Deer (Odocoileus virginianus) in Feeding Ixodes scapularis Larvae

Anaplasma phagocytophilum is a tick-borne bacterium and the causative agent of human granulocytic anaplasmosis. Two major variants have been identified in North America: a human pathogenic variant (Ap-ha) that is maintained by small mammals and a nonpathogenic variant (Ap-v1) that is maintained by white-tailed deer (Odocoileus virginianus). Despite white-tailed deer being recognized as the main reservoir of Ap-v1, few studies have directly demonstrated transmission of Ap-v1 from white-tailed deer to feeding I. scapularis ticks, and transmission to feeding larvae remains undescribed. In this study, we collected samples from an outdoor white-tailed deer research facility during an I. scapularis larval questing season in the eastern United States to investigate the variants infecting white-tailed deer and acquisition by feeding larvae. Although both variants were present in questing ticks onsite, white-tailed deer were persistently infected with only Ap-v1 and transferred this variant to feeding I. scapularis larvae with high efficiency. These results support the concept that white-tailed deer play a role in the maintenance of Ap-v1 in nature and highlight the utility of captive white-tailed deer research facilities for studying vector–pathogen–host biology.