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Daniel A Grear

Dan Grear is a Wildlife Disease Ecologist at the National Wildlife Health Center.

I am interested in mechanisms that cause heterogeneities in pathogen transmission in wild animal disease systems and at the interface of wildlife, domestic animal, and human health. I lead investigations into wildlife mortality events and research that incorporates field studies with theoretical modeling of disease systems to identify key mechanisms that drive transmission dynamic.

Professional Experience

  • 2015 - Present Wildlife Disease Ecologist, U.S. Geological Survey, National Wildlife Health Center, Madison, WI

  • 2013 - 2015 Ecologist, U.S. Department of Agriculture, Veterinary Services, Center for Epidemiology and Animal Health, Fort Collins, CO

  • 2011 - 2014 Post-Doctoral Researcher, Colorado State University

Education and Certifications

  • 2011 Ph.D. Ecology, Pennsylvania State University

  • 2006 M.S. Wildlife Ecology, University of Wisconsin

  • 2002 B.S. Wildlife Ecology, University of Wisconsin

Affiliations and Memberships*

  • Member of the Ecological Society of America

  • Member of the Wildlife Society

  • Bsal Task Force Working Group Member

Science and Products

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Aedes albopictus mosquito

Forecasting Mosquito Phenology in a Shifting Climate: Synthesizing Continental-scale Monitoring Data

Climate change is expected to have significant effects on the phenology of vectors of arthropod-borne diseases, particularly mosquitoes. However, forecasting the direction and magnitude of future phenological shifts requires a more detailed understanding of the climate drivers of mosquito phenology. Addressing this knowledge gap is particularly salient for mosquitoes, as they have the potential to
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John Wesley Powell Center for Analysis and Synthesis
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Forecasting Mosquito Phenology in a Shifting Climate: Synthesizing Continental-scale Monitoring Data

Climate change is expected to have significant effects on the phenology of vectors of arthropod-borne diseases, particularly mosquitoes. However, forecasting the direction and magnitude of future phenological shifts requires a more detailed understanding of the climate drivers of mosquito phenology. Addressing this knowledge gap is particularly salient for mosquitoes, as they have the potential to
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Northern gannet flying with mountains in background.

Avian Influenza

Avian influenza is a viral disease caused by various strains of avian influenza viruses that can be classified as low pathogenic avian influenza (LPAI) or highly pathogenic avian influenza (HPAI). It remains a global disease with potential high consequence with the potential to threaten wildlife, agriculture, and human health.
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Ecosystems Mission Area, Biological Threats and Invasive Species Research Program, National Wildlife Health Center
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Avian Influenza

Avian influenza is a viral disease caused by various strains of avian influenza viruses that can be classified as low pathogenic avian influenza (LPAI) or highly pathogenic avian influenza (HPAI). It remains a global disease with potential high consequence with the potential to threaten wildlife, agriculture, and human health.
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Scientist swabbing newt.

Batrachochytrium salamandrivorans (Bsal) Surveillance

Scientists of the USGS National Wildlife Health Center (NWHC) in collaboration with partners have developed risk assessments for Batrachochytrium salamandrivorans (Bsal) in the United States and have begun sampling high-risk locations for the fungus.
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Ecosystems Mission Area, Biological Threats and Invasive Species Research Program, National Wildlife Health Center
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Batrachochytrium salamandrivorans (Bsal) Surveillance

Scientists of the USGS National Wildlife Health Center (NWHC) in collaboration with partners have developed risk assessments for Batrachochytrium salamandrivorans (Bsal) in the United States and have begun sampling high-risk locations for the fungus.
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Image: Three-lined Salamander

Batrachochytrium salamandrivorans (Bsal)

Batrachochytrium salamandrivorans (Bsal) is an emerging pathogen capable of causing significant morbidity and mortality in salamanders.
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Ecosystems Mission Area, Biological Threats and Invasive Species Research Program, National Wildlife Health Center
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Batrachochytrium salamandrivorans (Bsal)

Batrachochytrium salamandrivorans (Bsal) is an emerging pathogen capable of causing significant morbidity and mortality in salamanders.
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Population genetic analysis of the snake-infecting fungus, Ophidiomyces ophidiicola, in the eastern United States

Snake fungal disease (SFD; ophidiomycosis), caused by the pathogen Ophidiomyces ophidiicola (Oo), has been documented in wild snakes in North America and Eurasia, and is a potentially emerging disease in the eastern USA. However, a lack of historical disease data has made it challenging to determine whether Oo is a recent arrival to the USA or whether SFD emergence is due to other factors. Here, w
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Biological Threats and Invasive Species Research Program, National Wildlife Health Center

Amphibian Chytrid Swab Data from Churchill County, Nevada (2019-2021)

This dataset includes results from external skin swabbing of Anaxyrus williamsi and Lithobates catesbeianus to test for the fungus Batrachochytrium dendrobatidis from the Dixie Valley in Churchill County, Nevada, in 2019-2021.
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Western Ecological Research Center (WERC)

Data from a national survey for the amphibian chytrid fungus Batrachochytrium salamandrivorans

This dataset provides the results of a national survey of the conterminous U.S. for the salamander chytrid fungus Batrachochytrium salamandrivorans (Bsal) conducted by the U.S. Geological Survey Amphibian Research and Monitoring Initiative from May 2014 to August 2017. Sites were sampled by capturing amphibians by hand or by traps or nets that were then swabbed individually using methods that prev
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Wetland and Aquatic Research Center

Pathology and bacteriology of 178 tadpoles with histologically confirmed Severe Perkinsea Infections: Data

(i) This dataset presents macroscopic and microscopic pathological findings and bacteriology of 178 tadpoles diagnosed with Severe Perkinsea Infections. (ii) Specimen were collected and submitted to the NWHC as part of mortality investigations and collection of specimen from apparently healthy populations as part of ongoing amphibian health monitoring. (iii) Necropsies and gross evaluation of carc
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Ecosystems Mission Area, Biological Threats and Invasive Species Research Program, National Wildlife Health Center

Pathogenic lineage of Perkinsea causes mass mortality of frogs across the USA: Data

Severe perkinsea data was based on the observation of characteristic gross and microscopic lesions and the morphological identification of Perkinsea organisms within the lesions. Necropsies and gross evaluation of carcasses were carried out under a dissecting microscope. Specimen were collected and submitted to the NWHC as part of mortality investigations and collection of specimen from apparently
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Ecosystems Mission Area, Biological Threats and Invasive Species Research Program, National Wildlife Health Center
Dark colored newt on bright green vegetation.
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Filter Total Items: 33

Epistylis spp. infestation in two species of mud turtles (Kinosternon spp.) in the American Southwest

The protistan genus Epistylis contains freshwater colonial species that attach to aquatic organisms in an epibiotic or parasitic relationship. They are known to attach to the epidermis and shells of aquatic turtles, but have not been reported to cause heavy infestations or morbidity in turtles. We documented heavy infestations of >Epistylis spp. in several populations of Sonoran mud turtles (Kinos
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Ecosystems Mission Area, National Wildlife Health Center

The population genetics of the causative agent of snake fungal disease indicate recent introductions to the USA

Snake fungal disease (SFD; ophidiomycosis), caused by the pathogen Ophidiomyces ophiodiicola (Oo), has been documented in wild snakes in North America and Eurasia, and is considered an emerging disease in the eastern United States of America. However, a lack of historical disease data has made it challenging to determine whether Oo is a recent arrival to the USA or whether SFD emergence is due to
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Ecosystems Mission Area, National Wildlife Health Center, Wetland and Aquatic Research Center

Quarterly Wildlife Mortality Report October 2021

The USGS National Wildlife Health Center (NWHC) Quarterly Mortality Report provides brief summaries of epizootic mortality and morbidity events by quarter. The write-ups, highlighting epizootic events and other wildlife disease topics of interest, are published in the Wildlife Disease Association quarterly newsletter. A link is provided in this WDA newsletter to the Wildlife Health Information Sha
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Ecosystems Mission Area, National Wildlife Health Center

Acute mortality in California tiger salamander (Ambystoma californiense) and Santa Cruz long-toed salamander (Ambystoma macrodactylum croceum) caused by Ribeiroia ondatrae (Class: Trematoda)

In early September 2019, a morbidity and mortality event affecting California tiger salamanders (Ambystoma californiense) and Santa Cruz long-toed salamanders (Ambystoma macrodactylum croceum) in late stages of metamorphosis was reported at a National Wildlife Refuge in Santa Cruz County, California, U.S.A. During the postmortem disease investigation, severe integumentary metacercarial (Class: Tre
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Ecosystems Mission Area, National Wildlife Health Center

Highly pathogenic avian influenza virus H5N2 (Clade 2.3.4.4) challenge of mallards age appropriate to the 2015 midwestern poultry outbreak

BackgroundThe 2015 highly pathogenic avian influenza virus (HPAIV) H5N2 clade 2.3.4.4 outbreak in upper midwestern U.S. poultry operations was not detected in wild birds to any great degree during the outbreak, despite wild waterfowl being implicated in the introduction, reassortment, and movement of the virus into North America from Asia. This outbreak led to the demise of over 50 million domesti
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Ecosystems Mission Area, National Wildlife Health Center

Evaluation of regulatory action and surveillance as preventive risk-mitigation to an emerging global amphibian pathogen Batrachochytrium salamandrivorans (Bsal)

The emerging amphibian pathogen Batrachochytrium salamandrivorans (Bsal) is a severe threat to global urodelan (salamanders, newts, and related taxa) biodiversity. Bsal has not been detected, to date, in North America, but the risk is high because North America is one of the global hotspots for urodelan biodiversity. The North American and United States response to the discovery of Bsal in Europe
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Ecosystems Mission Area, Eastern Ecological Science Center, National Wildlife Health Center, Patuxent Wildlife Research Center

Quarterly wildlife mortality report January 2021

The USGS National Wildlife Health Center (NWHC) Quarterly Mortality Report provides brief summaries of epizootic mortality and morbidity events by quarter. The write-ups, highlighting epizootic events and other wildlife disease topics of interest, are published in the Wildlife Disease Association quarterly newsletter. A link is provided in this WDA newsletter to the Wildlife Health Information Sha
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Ecosystems Mission Area, National Wildlife Health Center

Quarterly wildlife mortality report October 2020

The USGS National Wildlife Health Center (NWHC) Quarterly Mortality Report provides brief summaries of epizootic mortality and morbidity events by quarter. The write-ups, highlighting epizootic events and other wildlife disease topics of interest, are published in the Wildlife Disease Association quarterly newsletter. A link is provided in this WDA newsletter to the Wildlife Health Information Sha
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Ecosystems Mission Area, National Wildlife Health Center

Batrachochytrium salamandrivorans (Bsal) not detected in an intensive survey of wild North American amphibians

The salamander chytrid fungus (Batrachochytrium salamandrivorans [Bsal]) is causing massive mortality of salamanders in Europe. The potential for spread via international trade into North America and the high diversity of salamanders has catalyzed concern about Bsal in the U.S. Surveillance programs for invading pathogens must initially meet challenges that include low rates of occurrence on the l
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Ecosystems Mission Area, Eastern Ecological Science Center, National Wildlife Health Center, Northern Rocky Mountain Science Center, Patuxent Wildlife Research Center, Upper Midwest Environmental Sciences Center, Western Ecological Research Center (WERC), Wetland and Aquatic Research Center

Avian influenza virus prevalence in marine birds is dependent on ocean temperatures

Waterfowl and shorebirds are the primary hosts of influenza A virus (IAV), however, in most surveillance efforts, large populations of birds are not routinely examined; specifically marine ducks and other birds that reside predominately on or near the ocean. We conducted a long-term study sampling sea ducks and gulls in coastal Maine for IAV and found a virus prevalence (1.7%) much lower than is t
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Ecosystems Mission Area, Fish & Wildlife Disease (unpublished), National Wildlife Health Center

The ecology of chronic wasting disease in wildlife

Prions are misfolded infectious proteins responsible for a group of fatal neurodegenerative diseases termed transmissible spongiform encephalopathy or prion diseases. Chronic Wasting Disease (CWD) is the prion disease with the highest spillover potential, affecting at least seven Cervidae (deer) species. The zoonotic potential of CWD is inconclusive and cannot be ruled out. A risk of infection for
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Ecosystems Mission Area, Biological Threats and Invasive Species Research Program, National Wildlife Health Center

Quarterly wildlife mortality report April 2019

No abstract available.
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Ecosystems Mission Area, National Wildlife Health Center

Non-USGS Publications**

Gorsich EE, Luis AD, Buhnerkempe MG, Grear DA, Portacci K, Miller RS, Webb CT. 2016. Mapping US cattle shipment networks: Spatial and temporal patterns of trade communities from 2009 to 2011. Preventive Veterinary Medicine, 134, 82-91.
Lavelle MJ, Kay SL, Pepin KM, Grear DA, Campa H, VerCauteren K. 2016. Evaluating wildlife-cattle contact rates to improve the understanding of dynamics of bovine tuberculosis transmission in Michigan, USA. Preventive Veterinary Medicine, 135, 28-36.
Scott A, B McCluskey, M Brown-Reid, DA Grear, P Pitcher, G Ramos, D Spencer. 2016. Porcine epidemic diarrhea virus introduction into the United States: Root cause investigation. Preventive Veterinary Medicine, 123, 192-201. doi: 10.1016/j.prevetmed.2015.11.013
Glaser L, M Carstensen, S Shaw, S Robbe-Austerman, A Wunschmann, DA Grear, T Stuber, B Thomsen. 2016. Descpriptive epidemiology and whole genome sequencing analysis for an outbreak of bovine tuberculosis in beef cattle and white-tailed deer in Northwestern Minnesota. PLoS ONE, e0145735.
McClure RSM, CL Burdett, ML Farnsworth, MW Lutman, DM Theobold, PD Riggs, DA Grear, RS Miller. 2015. Modeling and mapping the probability of occurrence of invasive wild pigs across the contiguous United States. PLoS ONE 10(8): e0133771. doi:10.1371/journal.pone.0133771
Pepin KM, CB Leach, C Marques-Toledo, KH Laass, KS Paixao, AD Luis, DTS Hayman, NG Johnson, MG Buhnerkempe, S Carver, DA Grear, K Tsao, AE Eiras, and CT Webb. 2015. Utility of mosquito surveillance data for spatial prioritization of vector control against dengue viruses in three Brazilian cities. Parasites and Vectors, 8, 98.
Tsao K, S Robbe-Austerman, RS Miller, K Portacci, DA Grear, and CT Webb. 2014. Sources of bovine tuberculosis in the United States. Infection, Genetics, and Evolution. 114, 201-212.
Luong LT, DA Grear, and PJ Hudson. 2014. Manipulation of host-resource dynamics impacts transmission of trophically transmitted parasites. International Journal for Parasitology, 44, 737-742.
Grear DA, J Kaneene, J Averill, and CT Webb. 2014. Local cattle movements in response to ongoing bovine TB zonation and regulations. Preventive Veterinary Medicine, 114, 201-212.
Buhnerkempe MG, MJ Tildesley, T Lindström, DA Grear, RS Miller, K Portacci, M Keeling, U Wennergren, and CT Webb. 2014. The impact of movements and animal density on continental scale cattle disease outbreaks in the United States. PLoS one, e91724.
Grear DA, LT Luong, and PJ Hudson. 2013. Network transmission inference: host behavior and parasite life-cycle make social networks meaningful in disease ecology, Ecological Applications, 23, 1906-1914.
Buhnerkempe, MG, DA Grear, RS Miller, K Portacci, J Lombard, and CT Webb. 2013. A national-scale picture of U.S. cattle movements obtained from Interstate Certificates of Veterinary Inspection data. Prev. Vet. Med., 112, 318-329.
Lindström T, DA Grear, MG Buhnerkempe, CT Webb, RS Miller, K Portacci, and U Wennergren. 2013. Bayesian approach for modeling cattle movements in the United States: scaling up a partially observed network. PLoS ONE,8, e53432. doi:10.1371/journal.pone.0053432
Grear DA, LT Luong, and PJ Hudson. 2012. Sex-biased transmission of a complex life-cycle parasite: why males matter. Oikos, 121, 1446-1453. doi: 10.1111/j.1600-0706.2012.20358.x
Blanchong, JA, DA Grear, BV Weckworth, DP Keane, KT Scribner, and MD Samuel. 2012. Effects of chronic wasting disease on reproduction and fawn harvest vulnerability in Wisconsin white-tailed deer. Journal of Wildlife Diseases, 48, 361-370.
Rogers K, S Robinson, MD Samuel, and DA Grear. 2011. Diversity and distribution of white-tailed deer mtDNA lineages in CWD outbreak areas in southern Wisconsin, USA. Journal of Toxicology and Environmental Health, 74, 1521-1535. doi: 10.1080/15287394.2011.618980
Grear DA and PJ Hudson. 2011. The dynamics of macroparasite host-self-infection: a study of the patterns and processes of pinworm (Oxyuridae) aggregation. Parasitology, 138, 619-617. doi: 10.1017/S0031182011000096.
Grear DA, MD Samuel, K Scribner, BV Weckworth, and JA Langenberg. 2010. Influence of genetic relatedness and spatial proximity on CWD transmission among female white-tailed deer. Journal of Applied Ecology, 47, 532-540.
Luong, LT, SE Perkins, DA Grear, A Rizzoli, and PJ Hudson. 2010. The relative importance of host characteristics and co-infection in generating variation in Heligmosomoides polygyrus fecundity. Parasitology, 137, 1003-1012.
Grear DA, SE Perkins, and PJ Hudson. 2009. Does elevated testosterone result in increased exposure and transmission of parasites? Ecology Letters, 12, 528-537.
Luong, LT, DA Grear, and PJ Hudson. 2009. Male hosts are responsible for the transmission of a trophically transmitted parasite, Pterygodermatites peromysci to the intermediate host in the absence of sex-biased infection. International Journal for Parasitology, 39, 1263-1268.
Grear DA, MD Samuel, JA Langenberg, and D Keane. 2006. Demographic patterns and harvest vulnerability of chronic wasting disease infected white-tailed deer in Wisconsin. Journal of Wildlife Management, 70, 546-553.

**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.

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Preventive actions in response to the Bsal threat reduced Bsal risk in the U.S.

Import regulations and a large surveillance effort have reduced the risk of Batrachochytrium salamandrivorans (Bsal) introduction to the United States...

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A Unified Research Strategy for Disease Management

As wildlife diseases increase globally, an understanding of host-pathogen relationships can elucidate avenues for management and improve conservation...

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Science and Products

*Disclaimer: Listing outside positions with professional scientific organizations on this Staff Profile are for informational purposes only and do not constitute an endorsement of those professional scientific organizations or their activities by the USGS, Department of the Interior, or U.S. Government