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updated December 17, 2012            Webb Lab          CSU Biology         Curriculum Vitae     Google scholar

a bit about me...
DanMountainsContact Information
E334 Anatomy/Zoology
Department of Biology
Colorado State University
Fort Collins, CO  80523
1.970.491.2133
dagrear <at> colostate.edu

Research Interests
I am an ecologist interested in how parasites (disease-causing organisms) interact with their hosts, as well as how host behaviors lead to interesting heterogeneities in parasite transmission. All of the intricate host-parasite-environment interactions that make up the transmission process fascinate me and motivate my research. Attempting to unravel the complexities of the transmission process has led me to investigate the roles of social behavior, maleness, and economically driven animal transport in the ecology of several different parasites and pathogens. My research addresses fundamental questions about the transmission process in disease ecology:
  1. What mechanisms drive heterogeneities in host exposure and what are the consequences for parasite transmission in wildlife?
  2. What are the key heterogeneities of individual hosts that generate super-spreaders?  Do these mechanisms influence parasite susceptibility, exposure, or both?
  3. What hosts should be targeted for managing diseases; especially in complex systems where wildlife, livestock, and human ecology is intertwined? 
I approach these questions using a combination of mathematical modeling to determine mechanistic drivers of disease transmission, statistical modeling to explain observations of host-parasite systems, and manipulative field experiments to test fundamental hypotheses about disease transmission processes. In addition, a central aim of my research is to leverage my experience in empirical settings with theoretical ecology to generate results that translate into applications at the wildlife-domestic animal interface.

cattle mooovement                mice, maleness, worms            chronic wasting disease                dengue

Education
2011    Ph.D. Ecology, Penn State University
2006    M.S. Wildlife Ecology, University of Wisconsin
2002    B.S. Wildlife Ecology, University of Wisconsin


Research Projects (most recent first)

CATTLE MOVEMENT   moo

National Scale Network & Disease Modeling: I currently work on a large collaborative project to model the nation-wide patterns of cattle shipments in the U.S. and integrate the movement models with disease models to create the first data-driven national-scale model of livestock disease spread. My work with this project involves using spatially explicit Bayesian models that predict cattle transports (host dispersal) with traditional compartmental models of disease transmission in a meta-population framework. Not only will the outcomes of this work be used to guide disease surveillance and response planning for a potential foot and mouth disease outbreak in the U.S., but it is also at the conceptual frontier of how disease systems are modeled in large and diverse structured populations. My current work with disease modeling of the U.S. cattle industry has me involved with the Research and Policy in Disease Dynamics foot-and-mouth disease workshops (NIH Fogarty International Center), USDA's bovine tuberculosis (TB) management group, and the National Institute for Mathematical Biological Synthesis (NIMBioS) bovine TB working group.
Wildlife-Livestock Interface, Bovine TB in Michigan: In collaboration with with the state of Michigan I am applying aspects of network and disease modeling to the bovine TB issues at the wildlife-livestock interface. I have helped develop Bayesian methods to generate true estimates of bovine TB in cattle and white-tailed deer that incorporates the uncertainties of the diagnostic tests and am building a mechanistic transmission model that incorporates cattle transports and white-tailed deer ecology.

Supervisor: Collen Webb
Collaborators: Mike Tildesley (Warwick University), Uno Wennergren (Linkoping), Tom Lindstrom (University of Sydney/Linkoping), Michael Buhnerkempe (UCLA), Marleen Werkman (Warwick), Matt Keeling (Warwick), Jason Lombard (USDA-APHIS), Katie Portacci (USDA-APHIS), Ryan Miller (USDA-APHIS), John Kaneene (Michigan State)


 MICE, WORMS, & MALENESS
squeak             poop                    net

The major theme of my PhD dissertation research was to adress how the mechanisms of infection and transmission are linked. These processes are intimately related because infection is necessary to generate transmission and transmission is necessary for new infection. I used experimental manipulations in a field system of small mammals (white-footed mice, Peromyscus leucopus; eastern chipmunks Tamias striatus) and their gastrointestinal helminth parasites (worms). I tested two major hypotheses of how transmission heterogeneities can be generated (these are not exclusive):
  1. Hormone mediated (testosterone) physiological interactions between a host and its parasites wormsproduces more transmission events from male hosts with high testosterone
  2. Behaviorally mediated inter-host interactions increases transmission because of testosterone-mediated changes in contact rates
I found that high testosterone levels in male white-footed mice caused behavioral changes in the entire population; increasing everyone's potential infection contacts, even though high testosterone did not generate any individual heterogeneity in the testosterone treated males. In separate experiments, I found that male hosts generated more transmission events than females, even though infections levels were similar and that foraging behaviors of eastern chipmunks can explain infection patterns (but only when foraging behaviors were properly matched to parasite transmission modes in a network analysis).

Advisor: Peter Hudson
Collaborators: Lien Luong (University of Alberta), Sarah Perkins (Cardiff University), Kurt Vandegrift (Penn State)


CHRONIC WASTING DISEASE IN WISCONSINdoefawn

Chronic wasting disease was discovered in wild Wisconsin white-tailed deer (Odocoileus virginianus) in 2002 and subsequent surveillance found infected deer clustered in southwestern Wisconsin. Part of the Wisconsin Department of Natural Resources initial control strategy was increased harvest in the CWD-infected area. My M.S. project took advantage of this harvest to examine how the matriarchical social structure of female white-tailed deer influenced infection patterns. I genotyped the female deer from the initial year's harvest and found that closely related females (full-sib, mother-daughter) had a greatly increased probability of infection compared to less-related deer harvested from the same area, suggesting that transmission within female social-groups is higher than between social groups and direct deer-deer transmission is important to the spread of CWD in Wisconsin.

Advisor: Mike Samuel
Collaborators: Julie Blanchong (Iowa State), Delwyn Keane (WVDL), Julie Langenberg (ICF, then Wisconsin DNR), Stacie Robinson (University of Wisconsin)


MANAGEMENT OF DENGUE VIRUS TRANSMISSION

I have recently begun a collaboration with chemical ecologists in Brazil, public health scientists in Puerto Rico, and mathematical ecologists at Colorado State to develop an ecological modeling and adaptive management framework to understand and guide management of dengue. I have led the grant writing of an NSF proposal submitted in December 2012 that seeks to use a cutting edge vector surveillance system that combines a chemically baited mosquito trap with an mobile information-technology system, developed by our Brazilian collaborators, that is deployed with unprecedented local spatio-temporal scale resolution and large-scale geographic extent through the academic spin-off company, Ecovec, S.A.

Collaborators: Alvaro Eiras (UFMG, Belo Horizonte, BR), Brett Ellis (Puerto Rico Entomology Surveillance Lab), Kim Pepin (NIH, Fogarty International Center), Colleen Webb (CSU)


Selected Publications
curriculum vitae

2013  Grear DA, Luong, LT, Hudson PJ. Network transmission inference: host behavior and parasite life-cycle
          make social networks meaningful in disease ecology, Ecological Applications, in press.

2013  Lindström T, DA Grear, MG Buhnerkempe, CT Webb, RS Miller, K Portacci, and U Wennergren.
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
2012  Grear DA,  LT Luong, and PJ Husdon. 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
2010  Grear DA, MD Samuel, K Scribner, BV Weckworth, and JA Langenberg. Influence of genetic relatedness
and spatial proximity on CWD transmission among female white-tailed deer.  Journal of Applied Ecology, 47, 532-540.
2009  Grear DA, SE Perkins, and PJ Hudson.  Does elevated testosterone result in increased exposure and
transmission of parasites?  Ecology Letters, 12, 528-537. (This paper has been designated a Faculty of 1000 “Must Read” factor 8)
2006  Grear DA, MD Samuel, JA Langenberg, and D Keane.  Demographic patterns of CWD prevalence and
harvest vulnerability of CWD infected white-tailed deer in Wisconsin.  Journal of Wildlife Management, 70, 546-553.