Data From: Prevalence and risk factors of Anaplasma infections in eastern moose (Alces alces americana) and winter ticks (Dermacentor albipictus) in Maine, United States

Eastern moose (Alces alces americana) are heavily parasitized by winter ticks (Dermacentor albipictus), the dominant cause of increased calf mortality in the northeastern United States. Although much work has focused on the direct negative effects of winter tick on moose, it remains unknown whether diseases transmitted by ticks may also affect moose health, or pose a risk to other species. In this study, we explored the role that moose and winter ticks play in transmission of the tick-borne bacterial pathogen, Anaplasma, which causes mild to severe illness in humans and domestic animals. Our objectives were to (1) estimate the prevalence of Anaplasma spp. in moose and winter tick, (2) determine the phylogenetic placement of these strains with respect to those found in other hosts and vectors, and (3) explore risk factors of Anaplasma infection in moose. A total of 157 moose (142 calves, 15 adults) were captured in western (n = 83) and northern (n = 74) Maine in 2017 and 2018. We screened for Anaplasma spp. in moose whole blood samples using a genus-specific PCR assay targeting the 16S rRNA gene. We found that over half (54%) of the moose were infected with Anaplasma bacteria, with a greater proportion of moose harboring Anaplasma-infections in the western (67%) versus northern study areas (38%). Male moose also exhibited a higher prevalence than females (63% vs. 47%).  In contrast, Anaplasma prevalence in winter ticks was low (<1%). Sequencing and phylogenetic analysis revealed that the single Anaplasma strain in moose was highly divergent from the strain in winter ticks, and most closely related to an uncharacterized North American cervid strain. We conclude that winter ticks are unlikely to play a significant role in Anaplasma transmission to moose, however high infection prevalence warrants further investigation into the impacts of the disease on moose health.