PREVALENCE AND RISK FACTORS OF ANAPLASMA INFECTIONS IN EASTERN MOOSE (ALCES ALCES AMERICANA) AND WINTER TICKS (DERMACENTOR ALBIPICTUS) IN MAINE, USA.

Eastern moose (Alces alces americana) are heavily parasitized by winter ticks (Dermacentor albipictus), the dominant cause of increased calf mortality in the northeastern US. 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. We explored the role that moose and winter ticks play in transmission of the tick-borne bacterial pathogens, Anaplasma spp., which cause mild to severe illness in humans and domestic animals. Our objectives were to 1) estimate the prevalence of Anaplasma spp. in moose and winter ticks; 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. 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 exhibited a higher prevalence than did females (63% vs. 47%). In contrast, Anaplasma spp. 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 Anaplasma spp. infection on moose health.

Vertical transmission of the entomopathogenic soil fungus Scopulariopsis brevicaulis as a contaminant of eggs in the winter tick, Dermacentor albipictus, collected from calf moose (New Hampshire, USA).

Moose naturally acquire soil fungi on their fur that are entomopathogenic to the winter tick, Dermacentor albipictus. Presumed to provide a measure of on-host tick control, it is unknown whether these soil fungi impact subsequent off-host stages of the tick. Eggs and resultant larvae originating from engorged, adult female winter ticks collected from dead calf moose (Alces alces) were used to investigate the presence and extent of fungal infection. Approximately 40% of eggs and larvae were infected, almost exclusively by the fungus Scopulariopsis brevicaulis (teleomorph Microascus brevicaulis: Microascaceae, Ascomycota). Eggs analysed on the day of oviposition and day of hatching had high frequency (40%) of S. brevicaulis, whereas the frequency in eggs harvested in utero was minimal (7%); therefore, exposure occurs pre-oviposition in the female's genital chamber, not by transovarial transmission. At hatching, larvae emerge containing S. brevicaulis indicating transstadial transmission. Artificial infection by topical application of eggs and larvae with a large inoculum of S. brevicaulis spores caused rapid dehydration, marked mortality; pathogenicity was confirmed by Koch's postulates. The high hatching success (>90%) and multi-month survival of larvae imply that S. brevicaulis is maintained as a natural pathobiont in winter ticks.

Tick development on sexually-active bull moose is more advanced compared to that of cow moose in the winter tick, Dermacentor albipictus.

We performed a complete survey of ticks on 100 cm2 skin samples collected from 30 moose (Alces alces) harvested in 2017 in central and northern Maine, U.S.A. The samples were collected from 15 bulls, 13 cows, and 2 calves in mid-October when moose are breeding and winter ticks (Dermacentor albipictus) quest for a host. We identified only winter ticks with 99.2% in a juvenile stage; 3 adult ticks were found. Unfed nymphs were most common on bulls, whereas most ticks were fed larvae on cows and calves. The mean total count on bull samples was 21 ±â€¯4.4 (range = 0-55) and higher than on cows (6 ±â€¯0.5; range = 2-8). Unlike previous surveys, tick abundance was lowest on calves. Tick abundance was independent of age or weight of adult moose. The higher abundance and more rapid development of winter ticks on adult bulls likely reflects the seasonal influence of increased movements and hormonal cycles associated with reproduction.

Low and high thermal tolerance characteristics for unfed larvae of the winter tick Dermacentor albipictus (Acari: Ixodidae) with special reference to moose.

We report that larvae of the winter tick Dermacentor albipictus, the only stage that will quest for a host, can tolerate short-term cold shock down to -25°C and short-term heat shock as high as 46°C. Unlike a three host-tick, larvae of D. albipictus have no preconditioning response to low or high temperature exposure by rapid cold hardening (RCH) or heat hardening, and poor ability to acclimate to low and high temperature extremes. Thermal tolerance limits were not improved as the result of larval clustering, and there was only a minimal effect due to changes in photoperiod. These larvae are freeze intolerant and die at higher temperatures (-5 to -10°C) from contact with ice by inoculative freezing. In absence of cold-associated resistance mechanisms, winter survival requires that larvae procure a host before the first snow cover. Their low and high temperature tolerance, however, is a key survival element that adapts them for off-host periods during summer, which in the arctic could allow for northern expansion.