Resource selection by New York City deer reveals the effective interface between wildlife, zoonotic hazards and humans.

Although the role of host movement in shaping infectious disease dynamics is widely acknowledged, methodological separation between animal movement and disease ecology has prevented researchers from leveraging empirical insights from movement data to advance landscape scale understanding of infectious disease risk. To address this knowledge gap, we examine how movement behaviour and resource utilization by white-tailed deer (Odocoileus virginianus) determines blacklegged tick (Ixodes scapularis) distribution, which depend on deer for dispersal in a highly fragmented New York City borough. Multi-scale hierarchical resource selection analysis and movement modelling provide insight into how deer's movements contribute to the risk landscape for human exposure to the Lyme disease vector-I. scapularis. We find deer select highly vegetated and accessible residential properties which support blacklegged tick survival. We conclude the distribution of tick-borne disease risk results from the individual resource selection by deer across spatial scales in response to habitat fragmentation and anthropogenic disturbances.

Experimental oral delivery of the systemic acaricide moxidectin to free-ranging white-tailed deer (Artiodactyla: Cervidae) parasitized by Amblyomma americanum (Ixodida: Ixodidae).

Orally delivered, host-targeted, systemic acaricide treatment has potential to be an effective areawide tick abatement strategy. Past efforts using ivermectin for livestock were reported effective at controlling both Amblyomma americanum (L.) and Ixodes scapularis Say on Odocoileus virginianus (Zimmermann). However, the labeled 48-day withdrawal period for human consumption largely prevented utilization of this strategy targeting I. scapularis in autumn, when peak adult host-seeking activity coincides with regulated white-tailed deer hunting seasons. The modern-day compound moxidectin is the active ingredient in the pour-on formulation Cydectin (5 mg moxidectin/ml; Bayer Healthcare LLC), with a labeled 0-day withdrawal period for human consumption of treated cattle. We sought to re-examine the systemic acaricide approach for tick management by determining if we could successfully deliver Cydectin to free-ranging white-tailed deer. Over 2 yr in late spring/early summer, coinciding with adult and nymphal A. americanum activity, we fed Cydectin-coated corn to free-ranging white-tailed deer in coastal Connecticut. Through serum analysis, we documented moxidectin levels at or above those previously reported effective for control of ectoparasites (5-8 ppb for moxidectin and ivermectin) in 24 of 29 white-tailed deer captured (83%) while exposed to treated corn. While we did not document differences in burdens of parasitizing A. americanum based on moxidectin sera levels, we did document fewer engorged specimens on deer with increased sera levels. The systemic use of moxidectin for tick management in critical reproductive hosts has the potential to be effective in an areawide capacity while also permitting human consumption of treated venison.

Detection of SARS-CoV-2 Omicron variant (B.1.1.529) infection of white-tailed deer.

White-tailed deer ( Odocoileus virginianus ) are highly susceptible to infection by SARS-CoV-2, with multiple reports of widespread spillover of virus from humans to free-living deer. While the recently emerged SARS-CoV-2 B.1.1.529 Omicron variant of concern (VoC) has been shown to be notably more transmissible amongst humans, its ability to cause infection and spillover to non-human animals remains a challenge of concern. We found that 19 of the 131 (14.5%; 95% CI: 0.10-0.22) white-tailed deer opportunistically sampled on Staten Island, New York, between December 12, 2021, and January 31, 2022, were positive for SARS-CoV-2 specific serum antibodies using a surrogate virus neutralization assay, indicating prior exposure. The results also revealed strong evidence of age-dependence in antibody prevalence. A significantly (χ 2 , p < 0.001) greater proportion of yearling deer possessed neutralizing antibodies as compared with fawns (OR=12.7; 95% CI 4-37.5). Importantly, SARS-CoV-2 nucleic acid was detected in nasal swabs from seven of 68 (10.29%; 95% CI: 0.0-0.20) of the sampled deer, and whole-genome sequencing identified the SARS-CoV-2 Omicron VoC (B.1.1.529) is circulating amongst the white-tailed deer on Staten Island. Phylogenetic analyses revealed the deer Omicron sequences clustered closely with other, recently reported Omicron sequences recovered from infected humans in New York City and elsewhere, consistent with human to deer spillover. Interestingly, one individual deer was positive for viral RNA and had a high level of neutralizing antibodies, suggesting either rapid serological conversion during an ongoing infection or a "breakthrough" infection in a previously exposed animal. Together, our findings show that the SARS-CoV-2 B.1.1.529 Omicron VoC can infect white-tailed deer and highlights an urgent need for comprehensive surveillance of susceptible animal species to identify ecological transmission networks and better assess the potential risks of spillback to humans. KEY FINDINGS: These studies provide strong evidence of infection of free-living white-tailed deer with the SARS-CoV-2 B.1.1.529 Omicron variant of concern on Staten Island, New York, and highlight an urgent need for investigations on human-to-animal-to-human spillovers/spillbacks as well as on better defining the expanding host-range of SARS-CoV-2 in non-human animals and the environment.

Control and Surveillance Operations to Prevent Chronic Wasting Disease Establishment in Free-Ranging White-Tailed Deer in Québec, Canada.

Chronic wasting disease (CWD), a degenerative and fatal prion disease affecting cervids, was detected for the first time in the province of Québec, Canada, in a red deer (Cervus elaphus) farm in the Laurentides region on 10 September 2018. To assess CWD prevalence and control the disease in the free-ranging white-tailed deer (Odocoileus virginianus) population, a response plan including enhanced surveillance, population control, regulatory measures, and public outreach was deployed by the Ministry of Forests, Wildlife, and Parks (MFFP). In the 401 km2 white-tailed deer control area, a total of 750 free-ranging white-tailed deer were culled over 70 days, from 22 September to 15 December 2018. Of the culled deer, 534 were tested for CWD. We also tested for CWD a total of 447 white-tailed deer hunted from the enhanced surveillance zone and 2584 free-ranging white-tailed deer harvested outside this zone. Regulations were applied to prevent the spread of the disease through movements of infected animals harvested by hunters. Although no case of CWD was detected in free-ranging cervids in Québec in 2018, this does not confirm the absence of the disease in these populations. However, the results suggest that if CWD is present, few free-ranging cervids are infected, making it possible to prevent its establishment in the province of Québec.

Assessment of humaneness using gunshot targeting the brain and cervical spine for cervid depopulation under field conditions.

Population reduction or eradication of domestic or non-domestic species may be required to address their impacts on the environment, other species, or human interests. Firearms are often used to accomplish these practical management objectives, and there is increased concern that the methods used may compromise animal welfare. We document the accuracy and humaneness of gunshot placement to the brain and cervical vertebrae of Philippine deer (Rusa marianna) on Guam during depopulation activities as a model for meeting AVMA standards of euthanasia under field conditions (e.g., animal is not in hand). Deer were shot with a .223 caliber rifle from 10-125 m and approached immediately (<20 s) for assessment. A subset of adult deer was further evaluated for physiological responses including cessation of heart rate, respiration, ocular reflexes, and post-mortem spasms. All deer shot in the brain (n = 132) and upper cervical spine (C1-C3; n = 18) died immediately due to the destruction of the brain or spinal tissue. Shot placements were all within 1.9 cm of the point of aim (i.e., the center of the target region). The accuracy and immediate insensibility resulting from targeting of C1-C3 demonstrates that this is an alternative target site when animal positioning is not optimal for targeting the brain, or there is a need to preserve brain tissue (e.g., Chronic Wasting Disease testing). While targeting of C4 -C7 vertebrae (n = 6) was accurate and resulted in immediate incapacitation, the failure to produce immediate insensibility does not support the use of this shot placement when upper cervical or brain shot placement is an option. It is reasonable to achieve sufficient accuracy to target the brain or upper cervical vertebrae of deer under field conditions and meet standards of euthanasia while accomplishing management objectives.

Topical treatment of white-tailed deer with an acaricide for the control of Ixodes scapularis (Acari: Ixodidae) in a Connecticut Lyme borreliosis hyperendemic Community.

The 4-Poster device for the topical treatment of white-tailed deer, Odocoileus virginianus (Zimmermann), against ticks using the acaricide amitraz, was evaluated in a Lyme borreliosis endemic community in Connecticut. As part of a 5-year project from 1997 to 2002, 21-24 of the 4-Posters were distributed at residential sites in Old Lyme, CT, in a core treatment area of approximately 5.2 km(2) in fall 1997. The 4-Posters were active October to mid-December and March into May, corresponding to the peak periods of activity for adult Ixodes scapularis in this particular area. Corn consumption ranged from 361 to 4789 kg/month for October and November and 696-3130 kg/month during April. Usage of 4-Posters by deer generally was high (>90%), except during acorn masts in fall 1998 and 2001. Amitraz was applied by rollers at the estimated rate of 1.3 g active ingredient/ha/year. The abundance of host-seeking I. scapularis nymphs declined significantly (p < 0.001) in the core treatment area, as compared to a control community in Old Saybrook, CT, through 2004, over the project period from 1998 to 2003, from 9.3/100m(2) to 0.97/100m(2), rising to 1.90/100m(2) in 2004. From 1999 through 2003, there were 46.1%, 49.6%, 63.4%, 64.6%, and 70.2% reductions, respectively, in the nymphal tick population in comparison with the untreated community and initial tick abundance in 1998. Control of I. scapularis adults declined to only 19.1% in 2004; 2 years after the treatment of deer was discontinued. Differences in nymphal tick abundance between the control and core treatment area were significant in 1999 (p = 0.042) and highly significant in 2001 (p < 0.001) and 2002 (p = 0.002). The passive topical application to deer of the acaricide amitraz resulted in a significant decrease in the population of free-living I. scapularis nymphs in the treated core in Connecticut.

Acaricidal treatment of white-tailed deer to control Ixodes scapularis (Acari: Ixodidae) in a New York Lyme disease-endemic community.

The efficacy of topically treating white-tailed deer with an acaricide was evaluated in a Lyme disease-endemic community of southern New York State. Twenty-four 4-Poster feeders were placed in a 5.2 km(2) treatment area in Bedford, NY, while a site in Lewisboro, NY, 4.8 km distant, served as control. Treatment periods ran from 15 September to 15 December each fall from 1997 to 2001, and from 15 March to 15 May each spring from 1998 to 2002. Corn consumption averaged 15,779 kg in fall sessions and 9054 kg in spring sessions, and a mean of 89.6% of deer in the study area showed evidence of using the feeders. Deer densities, estimated by aerial snow counts, averaged 22 and 28 deer per km(2) in Bedford and Lewisboro, respectively, over a 3-year period. Significant reductions in tick numbers on deer captured in the treatment area were noted in fall 1999 compared to deer captured at the control site. Drag sampling for nymphal host-seeking ticks indicated 63.6% control in 2001, which dropped to 54.8% the following year, but reached 80% in 2003. Higher-than-normal acorn production in 2001 that likely caused a drop in deer visitation to the feeders may have reduced efficacy against larval ticks in 2002. The 4-Poster effectively reduced the density of Ixodes scapularis, though the level of control is dependent on environmental factors that affect feeding behavior of white-tailed deer.

Reduced abundance of Ixodes scapularis (Acari: Ixodidae) and the tick parasitoid Ixodiphagus hookeri (Hymenoptera: Encyrtidae) with reduction of white-tailed deer.

The principal vector for the pathogens of Lyme disease, human granulocytic ehrlichiosis, and human babesiosis is the tick Ixodes scapularis Say. A chalcid wasp, Ixodiphagus hookeri, in the family Encyrtidae parasitizes populations of the tick on several islands or other geographically isolated sites in New England with high densities of these ticks and white-tailed deer (Odocoileus virginianus), the principal host for adult I. scapularis. Deer densities were reduced at a forested tract in Bridgeport and the Bluff Point Coastal Reserve in Groton, Connecticut, from levels exceeding 90 animals per km2 in 1992 (Bridgeport) and 1994 (Bluff Point) to 17 and 10 animals per km2, respectively, by fall 2001. Tick densities declined with sustained reductions in the population of white-tailed deer. Similarly, prevalence of tick parasitism by Ixodes hookeri declined at both sites from 30 to 25% to <1.0% and was significantly correlated with previous year's deer density at both sites (r(s) = 0.933 and r(s) = 0.867, P < or = 0.0001) and with nymphal tick densities at Bridgeport (r(s) = 0.867, P < or = 0.0001), but was not as well correlated with tick densities in Groton. The virtual disappearance of I. hookeri in this study corresponds with a lack of I. hookeri in mainland I. scapularis at comparable deer and tick densities, suggesting that there is a threshold deer density of approximatley 10-20/km2, with corresponding tick densities necessary for I. hookeri to successfully parasitize I. scapularis.