High Prevalence and Broad Distribution of Trichomonas gypaetinii in Bald Eagles (Haliaceetus leucocephalus) in the USA.

Trichomonas gypaetinii was detected in 117 (88%) of 133 Bald Eagles (Haliaceetus leucocephalus) and in 0 of 7 Golden Eagles (Aquila chrysaetos) in the USA, with no sex or age prevalence difference. All eagles lacked associated lesions. This study indicated that T. gypaetinii is common and widespread in Bald Eagles, but rarely associated with disease.

BAITING AND BANDING: EXPERT OPINION ON HOW BAIT TRAPPING MAY INFLUENCE THE OCCURRENCE OF HIGHLY PATHOGENIC AVIAN INFLUENZA (HPAI) AMONG DABBLING DUCKS.

A Eurasian lineage highly pathogenic avian influenza virus (HPAIV) of the clade 2.3.4.4b (Goose/Guangdong lineage) was detected in migratory bird populations in North America in December 2021, and it, along with its reassortants, have since caused wild and domestic bird outbreaks across the continent. Relative to previous outbreaks, HPAIV cases among wild birds in 2022 exhibited wider geographic extent within North America and higher levels of mortality, suggesting the potential for population-level impacts. Given the possible conservation implications of HPAIV in wild birds, natural resource managers have sought guidance on actions that may mitigate negative effects of disease among North American bird populations, including modification of existing management practices. Banding of waterfowl is a critical tool for population management for several harvested species in North America, but some banding techniques, such as bait trapping, can lead to increased congregation of waterfowl, potentially altering HPAIV transmission. We used an expert opinion exercise to assess how bait trapping of dabbling ducks in Canada may influence HPAIV transmission and wild bird health. The expert group found that it is moderately likely that bait trapping of dabbling ducks in wetlands will significantly increase the transmission of HPAIV among individual ducks, but there is a low probability that this will result in significant population-level effects on North American dabbling ducks. Considering the lack of empirical work studying how capture and handling methods may change transmission of HPAIV among waterfowl, as well as the importance of bait trapping for waterfowl management in North America, future work should focus on filling knowledge gaps pertaining to the influence of baiting on HPAIV occurrence to better inform banding procedures and management decision making.

Bald eagle mortality and nest failure due to clade 2.3.4.4 highly pathogenic H5N1 influenza a virus.

The bald eagle (Haliaeetus leucocephalus) is a culturally and ecologically vital species in North America that embodies conservation success but continues to face threats that include emerging pathogens. The introduction of A/goose/Guangdong/1/1996 lineage highly pathogenic (HP) clade 2.3.4.4b H5N1 influenza A virus (IAV) in North America in late 2021 resulted in high rates of mortality among bald eagles. Here we show an alarming rate of bald eagle nest failure and mortality attributed to HP IAV. We documented fatal, systemic HP IAV infection in breeding adult and nestling bald eagles along the southeastern U.S. coast. Concurrently, annual bald eagle nest surveys in Georgia and Florida revealed a precipitous drop in success in coastal counties compared with previous years, portending negative impacts on population recruitment. As an apex predator and efficient scavenger, it is likely that bald eagles become infected through consumption of infected waterfowl. These results and similar reports of raptor mortality in Europe, Asia, and Africa, indicate a clear threat to raptor health. The possible long-term persistence of HP H5N1 IAV in North America poses an impending threat to bald eagle populations not only related to direct mortality but also decreased recruitment and warrants continued efforts to understand these potential impacts.

Age-specific survival rates, causes of death, and allowable take of golden eagles in the western United States.

In the United States, the Bald and Golden Eagle Protection Act prohibits take of golden eagles (Aquila chrysaetos) unless authorized by permit, and stipulates that all permitted take must be sustainable. Golden eagles are unintentionally killed in conjunction with many lawful activities (e.g., electrocution on power poles, collision with wind turbines). Managers who issue permits for incidental take of golden eagles must determine allowable take levels and manage permitted take accordingly. To aid managers in making these decisions in the western United States, we used an integrated population model to obtain estimates of golden eagle vital rates and population size, and then used those estimates in a prescribed take level (PTL) model to estimate the allowable take level. Estimated mean annual survival rates for golden eagles ranged from 0.70 (95% credible interval = 0.66-0.74) for first-year birds to 0.90 (0.88-0.91) for adults. Models suggested a high proportion of adult female golden eagles attempted to breed and breeding pairs fledged a mean of 0.53 (0.39-0.72) young annually. Population size in the coterminous western United States has averaged ~31,800 individuals for several decades, with λ = 1.0 (0.96-1.05). The PTL model estimated a median allowable take limit of ~2227 (708-4182) individuals annually given a management objective of maintaining a stable population. We estimate that take averaged 2572 out of 4373 (59%) deaths annually, based on a representative sample of transmitter-tagged golden eagles. For the subset of golden eagles that were recovered and a cause of death determined, anthropogenic mortality accounted for an average of 74% of deaths after their first year; leading forms of take over all age classes were shooting (~670 per year), collisions (~611), electrocutions (~506), and poisoning (~427). Although observed take overlapped the credible interval of our allowable take estimate and the population overall has been stable, our findings indicate that additional take, unless mitigated for, may not be sustainable. Our analysis demonstrates the utility of the joint application of integrated population and prescribed take level models to management of incidental take of a protected species.

Anticoagulant rodenticide exposure and toxicosis in bald eagles (Haliaeetus leucocephalus) and golden eagles (Aquila chrysaetos) in the United States.

Raptors, including eagles, are geographically widespread and sit atop the food chain, thereby serving an important role in maintaining ecosystem balance. After facing population declines associated with exposure to organochlorine insecticides such as dichlorodiphenyltrichloroethane (DDT), bald eagles (Haliaeetus leucocephalus) have recovered from the brink of extinction. However, both bald and golden eagles (Aquila chrysaetos) are exposed to a variety of other toxic compounds in the environment that could have population impacts. Few studies have focused on anticoagulant rodenticide (AR) exposure in eagles. Therefore, the purpose of this study was to determine the types of ARs that eagles are exposed to in the USA and better define the extent of toxicosis (i.e., fatal illness due to compound exposure). Diagnostic case records from bald and golden eagles submitted to the Southeastern Cooperative Wildlife Disease Study (University of Georgia) 2014 through 2018 were reviewed. Overall, 303 eagles were examined, and the livers from 116 bald eagles and 17 golden eagles were tested for ARs. The percentage of AR exposure (i.e., detectable levels but not associated with mortality) in eagles was high; ARs were detected in 109 (82%) eagles, including 96 (83%) bald eagles and 13 (77%) golden eagles. Anticoagulant rodenticide toxicosis was determined to be the cause of mortality in 12 (4%) of the 303 eagles examined, including 11 bald eagles and 1 golden eagle. Six different AR compounds were detected in these eagles, with brodifacoum and bromadiolone most frequently detected (81% and 25% of eagles tested, respectively). These results suggest that some ARs, most notably brodifacoum, are widespread in the environment and are commonly consumed by eagles. This highlights the need for research to understand the pathways of AR exposure in eagles, which may help inform policy and regulatory actions to mitigate AR exposure risk.

Algal plankton turn to hunting to survive and recover from end-Cretaceous impact darkness.

The end-Cretaceous bolide impact triggered the devastation of marine ecosystems. However, the specific kill mechanism(s) are still debated, and how primary production subsequently recovered remains elusive. We used marine plankton microfossils and eco-evolutionary modeling to determine strategies for survival and recovery, finding that widespread phagotrophy (prey ingestion) was fundamental to plankton surviving the impact and also for the subsequent reestablishment of primary production. Ecological selectivity points to extreme post-impact light inhibition as the principal kill mechanism, with the marine food chain temporarily reset to a bacteria-dominated state. Subsequently, in a sunlit ocean inhabited by only rare survivor grazers but abundant small prey, it was mixotrophic nutrition (autotrophy and heterotrophy) and increasing cell sizes that enabled the eventual reestablishment of marine food webs some 2 million years later.

Use of a multiagency approach to eradicate New World screwworm flies from Big Pine Key, Florida, following an outbreak of screwworm infestation (September 2016-March 2017).

On September 30, 2016, the US National Veterinary Services Laboratory confirmed an autochthonous case of New World screwworm infestation in a Key deer (Odocoileus virginianus clavium) from Big Pine Key, Fla. This case marked the first identification of a sustained and reproducing population of New World screwworm flies in the United States since 1966. Multiple federal, state, and local government agencies collaborated to initiate a response to the outbreak. Efforts were successful in eradicating the flies from Florida.

Diversity decoupled from ecosystem function and resilience during mass extinction recovery.

The Chicxulub bolide impact 66 million years ago drove the near-instantaneous collapse of ocean ecosystems. The devastating loss of diversity at the base of ocean food webs probably triggered cascading extinctions across all trophic levels1-3 and caused severe disruption of the biogeochemical functions of the ocean, and especially disrupted the cycling of carbon between the surface and deep sea4,5. The absence of sufficiently detailed biotic data that span the post-extinction interval has limited our understanding of how ecosystem resilience and biochemical function was restored; estimates6-8 of ecosystem 'recovery' vary from less than 100 years to 10 million years. Here, using a 13-million-year-long nannoplankton time series, we show that post-extinction communities exhibited 1.8 million years of exceptional volatility before a more stable equilibrium-state community emerged that displayed hallmarks of resilience. The transition to this new equilibrium-state community with a broader spectrum of cell sizes coincides with indicators of carbon-cycle restoration and a fully functioning biological pump9. These findings suggest a fundamental link between ecosystem recovery and biogeochemical cycling over timescales that are longer than those suggested by proxies of export production7,8, but far shorter than the return of taxonomic richness6. The fact that species richness remained low as both community stability and biological pump efficiency re-emerged suggests that ecological functions rather than the number of species are more important to community resilience and biochemical functions.

Warm plankton soup and red herrings: calcareous nannoplankton cellular communities and the Palaeocene-Eocene Thermal Maximum.

Past global warming events such as the Palaeocene-Eocene Thermal Maximum (PETM-56 Ma) are attributed to the release of vast amounts of carbon into the ocean, atmosphere and biosphere with recovery ascribed to a combination of silicate weathering and organic carbon burial. The phytoplanktonic nannoplankton are major contributors of organic and inorganic carbon but their role in this recovery process remains poorly understood and complicated by their contribution to marine calcification. Biocalcification is implicated not only in long-term carbon burial but also both short-term positive and negative climatic feedbacks associated with seawater buffering and responses to ocean acidification. Here, we use exceptional records of preserved fossil coccospheres to reconstruct cell size distribution, biomass production (particulate organic carbon, POC) and (particulate) inorganic carbon (PIC) yields of three contrasting nannoplankton communities (Bass River-outer shelf, Maud Rise-uppermost bathyal, Shatsky Rise-open ocean) through the PETM onset and recovery. Each of the sites shows contrasting community responses across the PETM as a function of their taxic composition and total community biomass. Our results indicate that nannoplankton PIC:POC had no role in short-term climate feedback and, as such, their importance as a source of CO2 to the environment is a red herring. It is nevertheless likely that shifts to greater numbers of smaller cells at the shelf site in particular led to greater carbon transfer efficiency, and that nannoplankton productivity and export across the shelves had a significant modulating effect on carbon sequestration during the PETM recovery.This article is part of a discussion meeting issue 'Hyperthermals: rapid and extreme global warming in our geological past'.

Experimental Infection of Common Eider Ducklings with Wellfleet Bay Virus, a Newly Characterized Orthomyxovirus.

Wellfleet Bay virus (WFBV), a novel orthomyxovirus in the genus Quaranjavirus, was first isolated in 2006 from carcasses of common eider (Somateria mollissima) during a mortality event in Wellfleet Bay (Barnstable County, Massachusetts, USA) and has since been repeatedly isolated during recurrent mortality events in this location. Hepatic, pancreatic, splenic, and intestinal necrosis was observed in dead eiders. We inoculated 6-week-old common eider ducklings with WFBV in an attempt to recreate the naturally occurring disease. Approximately 25% of inoculated eiders had onset of clinical disease and required euthanasia; an additional 18.75% were adversely affected based on net weight loss during the trial. Control ducklings did not become infected and did not have clinical disease. Infected ducklings with clinical disease had pathologic lesions consistent with those observed during natural mortality events. WFBV was reisolated from 37.5% of the inoculated ducklings. Ducklings surviving to 5 days postinoculation developed serum antibody titers to WFBV.

PREVALENCE AND DISTRIBUTION OF WELLFLEET BAY VIRUS EXPOSURE IN THE COMMON EIDER (SOMATERIA MOLLISSIMA).

Between 1998 and 2014, recurrent mortality events were reported in the Dresser's subspecies of the Common Eider ( Somateria mollissima dresseri) on Cape Cod, Massachusetts, US near Wellfleet Harbor. The early die-offs were attributed to parasitism and emaciation, but beginning in 2006 a suite of distinct lesions was observed concomitant with the isolation of a previously unknown RNA virus. This novel pathogen was identified as an orthomyxovirus in the genus Quaranjavirus and was named Wellfleet Bay virus (WFBV). To assess evidence of exposure to this virus in Common Eiders, we conducted a longitudinal study of the prevalence of WFBV antibodies at multiple locations from 2004-14; we collected 2,258 serum samples from six locations and analyzed each using a microneutralization assay. Results corroborate the emergence of WFBV in 2006 based on the first detection of antibodies in that year. Significantly higher prevalence was detected in Common Eiders sampled in Massachusetts compared to those in Maine, Nova Scotia, and Québec. For birds breeding and wintering in Massachusetss, viral exposure varied by age, sex, and season of sampling, and prevalence by season and sex were highly interrelated with greater numbers of antibody-positive males in the autumn and females in the spring. No evidence of viral exposure was detected in the Northern subspecies ( Somateria mollissima borealis). Among the locations sampled, Massachusetts appears to be the epicenter of Common Eider exposure to WFBV. Further research is warranted to understand the factors controlling the epidemiology of WFBV in Massachussetts, including those that may be limiting geographic expansion of this virus.

Why marine phytoplankton calcify.

Calcifying marine phytoplankton-coccolithophores- are some of the most successful yet enigmatic organisms in the ocean and are at risk from global change. To better understand how they will be affected, we need to know "why" coccolithophores calcify. We review coccolithophorid evolutionary history and cell biology as well as insights from recent experiments to provide a critical assessment of the costs and benefits of calcification. We conclude that calcification has high energy demands and that coccolithophores might have calcified initially to reduce grazing pressure but that additional benefits such as protection from photodamage and viral/bacterial attack further explain their high diversity and broad spectrum ecology. The cost-benefit aspect of these traits is illustrated by novel ecosystem modeling, although conclusive observations remain limited. In the future ocean, the trade-off between changing ecological and physiological costs of calcification and their benefits will ultimately decide how this important group is affected by ocean acidification and global warming.

HEALTH AND NUTRITIONAL ASSESSMENT OF FREE-RANGING EASTERN INDIGO SNAKES (DRYMARCHON COUPERI) IN GEORGIA, UNITED STATES.

Clinical pathology and nutritional parameters are useful in evaluating and monitoring threatened and endangered wildlife populations, but reference ranges for most snake species are lacking. From 2001 to 2005, health assessments were performed on 58 eastern indigo snakes (EIS) (Drymarchon couperi) captured in the wild in southeastern Georgia, United States. Health and nutritional assessments performed included hematology, serum biochemistry, fat-soluble vitamins, heavy metals, pesticide contaminants, parasitology, and surveys of other pathogens. Significant differences in total solids, packed cell volume, glucose, blood urea nitrogen, albumin : globulin ratio, amylase, triglycerides, and bile acids between males and females were observed. Additionally, there was a significant difference between liver and kidney concentrations for vitamins A and E. As previously noted in captive EIS, total Ca was elevated in comparison to concentrations reported in other snake species. Parasitism was a common finding in sampled EIS, but the overall health status of this free-ranging population appeared good. A winter-time dermatitis was found in most snakes, which resolved in the summer months. This study represents the first health and nutritional assessment of free-ranging EIS, and provides needed data to guide monitoring and conservation efforts.

Demographic and Spatiotemporal Patterns of Avian Influenza Infection at the Continental Scale, and in Relation to Annual Life Cycle of a Migratory Host.

Since the spread of highly pathogenic avian influenza (HPAI) H5N1 in the eastern hemisphere, numerous surveillance programs and studies have been undertaken to detect the occurrence, distribution, or spread of avian influenza viruses (AIV) in wild bird populations worldwide. To identify demographic determinants and spatiotemporal patterns of AIV infection in long distance migratory waterfowl in North America, we fitted generalized linear models with binominal distribution to analyze results from 13,574 blue-winged teal (Anas discors, BWTE) sampled in 2007 to 2010 year round during AIV surveillance programs in Canada and the United States. Our analyses revealed that during late summer staging (July-August) and fall migration (September-October), hatch year (HY) birds were more likely to be infected than after hatch year (AHY) birds, however there was no difference between age categories for the remainder of the year (winter, spring migration, and breeding period), likely due to maturing immune systems and newly acquired immunity of HY birds. Probability of infection increased non-linearly with latitude, and was highest in late summer prior to fall migration when densities of birds and the proportion of susceptible HY birds in the population are highest. Birds in the Central and Mississippi flyways were more likely to be infected compared to those in the Atlantic flyway. Seasonal cycles and spatial variation of AIV infection were largely driven by the dynamics of AIV infection in HY birds, which had more prominent cycles and spatial variation in infection compared to AHY birds. Our results demonstrate demographic as well as seasonal, latitudinal and flyway trends across Canada and the US, while illustrating the importance of migratory host life cycle and age in driving cyclical patterns of prevalence.

Wood ducks (Aix sponsa) as potential reservoirs for avian influenza and avian paramyxoviruses.

Influenza A viruses (IAVs) and avian paramyxoviruses (APMVs) are important pathogens of poultry worldwide, and both commonly occur in wild waterfowl, especially ducks in the family Anatidae. Although wood ducks (Aix sponsa) are members of the Anatidae, their behaviour differs from most other species in this family, which could affect the transmission of IAVs and APMVs. We collected cloacal and oropharyngeal swab and blood samples from more than 700 wood ducks across nine states in the eastern United States of America. No IAVs were isolated, and based on blocking enzyme-linked immunoassay ELISA results, antibodies to IAVs were only detected in 0.2% of samples. In contrast, 23 (3%) APMVs were isolated (22 Newcastle disease virus and 1 APMV-6), and antibodies to multiple serotypes of APMVs were detected in more than 60% of the samples. After-hatch-year birds were more likely to be antibody positive for APMV-4 and APMV-6 compared to hatch-year birds. Female birds were more likely to be antibody positive for APMV-4 than were male birds. Our results indicate that wood ducks are probably not an important host for IAV but are frequently infected with APMVs.

Cyclic avian mass mortality in the northeastern United States is associated with a novel orthomyxovirus.

UNLABELLED: Since 1998, cyclic mortality events in common eiders (Somateria mollissima), numbering in the hundreds to thousands of dead birds, have been documented along the coast of Cape Cod, MA, USA. Although longitudinal disease investigations have uncovered potential contributing factors responsible for these outbreaks, detecting a primary etiological agent has proven enigmatic. Here, we identify a novel orthomyxovirus, tentatively named Wellfleet Bay virus (WFBV), as a potential causative agent of these outbreaks. Genomic analysis of WFBV revealed that it is most closely related to members of the Quaranjavirus genus within the family Orthomyxoviridae. Similar to other members of the genus, WFBV contains an alphabaculovirus gp64-like glycoprotein that was demonstrated to have fusion activity; this also tentatively suggests that ticks (and/or insects) may vector the virus in nature. However, in addition to the six RNA segments encoding the prototypical structural proteins identified in other quaranjaviruses, a previously unknown RNA segment (segment 7) encoding a novel protein designated VP7 was discovered in WFBV. Although WFBV shows low to moderate levels of sequence similarity to Quaranfil virus and Johnston Atoll virus, the original members of the Quaranjavirus genus, additional antigenic and genetic analyses demonstrated that it is closely related to the recently identified Cygnet River virus (CyRV) from South Australia, suggesting that WFBV and CyRV may be geographic variants of the same virus. Although the identification of WFBV in part may resolve the enigma of these mass mortality events, the details of the ecology and epidemiology of the virus remain to be determined. IMPORTANCE: The emergence or reemergence of viral pathogens resulting in large-scale outbreaks of disease in humans and/or animals is one of the most important challenges facing biomedicine. For example, understanding how orthomyxoviruses such as novel influenza A virus reassortants and/or mutants emerge to cause epidemic or pandemic disease is at the forefront of current global health concerns. Here, we describe the emergence of a novel orthomyxovirus, Wellfleet Bay virus (WFBV), which has been associated with cyclic large-scale bird die-offs in the northeastern United States. This initial characterization study provides a foundation for further research into the evolution, epidemiology, and ecology of newly emerging orthomyxoviruses, such as WFBV, and their potential impacts on animal and/or human health.

Coccolithophore calcification response to past ocean acidification and climate change.

Anthropogenic carbon dioxide emissions are forcing rapid ocean chemistry changes and causing ocean acidification (OA), which is of particular significance for calcifying organisms, including planktonic coccolithophores. Detailed analysis of coccolithophore skeletons enables comparison of calcite production in modern and fossil cells in order to investigate biomineralization response of ancient coccolithophores to climate change. Here we show that the two dominant coccolithophore taxa across the Paleocene-Eocene Thermal Maximum (PETM) OA global warming event (~56 million years ago) exhibited morphological response to environmental change and both showed reduced calcification rates. However, only Coccolithus pelagicus exhibits a transient thinning of coccoliths, immediately before the PETM, that may have been OA-induced. Changing coccolith thickness may affect calcite production more significantly in the dominant modern species Emiliania huxleyi, but, overall, these PETM records indicate that the environmental factors that govern taxonomic composition and growth rate will most strongly influence coccolithophore calcification response to anthropogenic change.

Evaluation of a restriction fragment length enzyme assay for differentiation of Haemoproteus and Plasmodium across a standard region of the mitochondrial genome.

Avian hemosporidian parasites are a genetically diverse group of parasites with a near cosmopolitan distribution. Over the past 2 decades, several PCR protocols have been designed to detect these parasites. The majority of these protocols amplify part of or the entire mitochondrial cytochrome b gene. However, many of these protocols co-amplify 2 genera (Haemoproteus and Plasmodium), making it impossible to determine which genus is amplified without post-PCR analysis. A uniform database (MalAvi), containing sequences amplified with the primers HAEMF and HAEMR2, has been developed to increase comparability across studies. We analyzed sequences from the MalAvi database and new sequences and found that digestion with EcoRV could be used to distinguish Haemoproteus from the majority of Plasmodium sequences. In addition, we tested 220 wild birds from Costa Rica and the United States for avian hemosporidians and assessed the ability of EcoRV to distinguish these 2 genera. Thirty-six positive samples were sequenced to confirm the restriction profiles, and we also analyzed 63 new hemosporidian sequences from ongoing studies in the United States for the restriction site. Among these new samples, all of the 85 Haemoproteus (subgenus Parahaemoproteus) and 14 Plasmodium were distinguishable. Overall, 887 of 898 (98.8%) sequences from our studies and the MalAvi database were assigned to the correct genus. Of these samples, all Haemoproteus samples were correctly identified and all but 11 Plasmodium samples were correctly identified by the EcoRV assay. Overall, this restriction enzyme protocol is able to quickly and efficiently classify these 2 genera of avian malarial parasites and would be useful for researchers interested in identifying parasites to genus-level, studies focused on sequence analysis of only a single genus, or for detecting co-infections that would need cloning prior to sequence analysis.

The historical, present, and future role of veterinarians in One Health.

The renewed interest in the concept of One Health has occurred as a result of the increased emergence of zoonotic infectious diseases over the past decade. The subsequent impacts of these diseases on human, livestock, and wildlife health, as well as the economic effects, have given international health organizations and national governments a greater appreciation of the importance of collaborative efforts in solving health problems. The One Health concept is not new, but under its umbrella, a new generation of veterinarians, physicians, ecologists, biologists, and social scientists is shaping the concept in novel ways. This has led to increased support for One Health initiatives to control disease by international agencies, national governments, and nongovernmental organizations as well as a growing emphasis on One Health concepts in training the veterinary workforce. Veterinary schools are reorganizing veterinary education to better teach students the precepts of One Health. This chapter explores the evolution and application of the One Health concept from the perspective of the veterinarian. The veterinary profession is positioned to be a strong advocate and leader of One Health. Veterinarians have a long history of involvement with One Health activities, and this involvement has adjusted and shifted with the changing needs of society. A new area of work for veterinarians is ecosystem health, which is becoming more relevant as a result of the impact that the ever-increasing human population is having on the environment that supports them.

Morphologic and Molecular Characterization of a Demodex (Acari: Demodicidae) Species from White-Tailed Deer (Odocoileus virginianus).

Demodex mites, although usually nonpathogenic, can cause a wide range of dermatological lesions ranging from mild skin irritation and alopecia to severe furunculosis. Recently, a case of demodicosis from a white-tailed deer (Odocoileus virginianus) revealed a Demodex species morphologically distinct from Demodex odocoilei. All life cycle stages were considerably larger than D. odocoilei and although similar in size to D. kutzeri and D. acutipes from European cervids, numerous morphometrics distinguished the four species. Adult males and females were 209.1 ± 13.1 and 225.5 ± 13.4 µm in length, respectively. Ova, larva, and nymphs measured 65.1 ± 4.1, 124.9 ± 11.6, and 205.1 ± 19.4 µm in length, respectively. For phylogenetic analyses, a portion of the 18S rRNA gene was amplified and sequenced from samples of the WTD Demodex sp., two Demodex samples from domestic dogs, and Demodex ursi from a black bear. Phylogenetic analyses indicated that the WTD Demodex was most similar to D. musculi from laboratory mice. A partial sequence from D. ursi was identical to the WTD Demodex sequence; however, these two species can be differentiated morphologically. This paper describes a second Demodex species from white-tailed deer and indicates that 18S rRNA is useful for phylogenetic analysis of most Demodex species, but two morphologically distinct species had identical partial sequences. Additional gene targets should be investigated for phylogenetic and parasite-host association studies.