RESEARCH ARTICLE Landscape influence on spatial patterns of meningeal worm and liver fluke infection in white-tailed deer KIMBERLY L. VANDERWAAL 1,2 * , STEVE K. WINDELS 3 , BRYCE T. OLSON 3 , J. TREVOR VANNATTA 2 and RON MOEN 2 1 Conservation Department, Minnesota Zoo, 13000 Zoo Blvd., Apple Valley, Minnesota 55124, USA 2 Natural Resources Research Institute, University of Minnesota, Duluth. 5013 Miller Trunk Highway, Duluth, Minnesota 55811, USA 3 Voyageurs National Park, 360 Hwy 11. E, International Falls, Minnesota 56649, USA (Received 22 September 2014; revised 28 October 2014; accepted 29 October 2014) SUMMARY Parasites that primarily infect white-tailed deer (Odocoileus virginianus), such as liver flukes (Fascioloides magna) and meningeal worm (Parelaphostrongylus tenuis), can cause morbidity and mortality when incidentally infecting moose (Alces alces). Ecological factors are expected to influence spatial variation in infection risk by affecting the survival of free-living life stages outside the host and the abundance of intermediate gastropod hosts. Here, we investigate how ecology influenced the fine-scale distribution of these parasites in deer in Voyageurs National Park, Minnesota. Deer pellet groups (N = 295) were sampled for the presence of P. tenuis larvae and F. magna eggs. We found that deer were sig- nificantly more likely to be infected with P. tenuis in habitats with less upland deciduous forest and more upland mixed conifer forest and shrub, a pattern that mirrored microhabitat differences in gastropod abundances. Deer were also more likely to be infected with F. magna in areas with more marshland, specifically rooted-floating aquatic marshes (RFAMs). The environment played a larger role than deer density in determining spatial patterns of infection for both parasites, highlighting the importance of considering ecological factors on all stages of a parasite’s life cycle in order to understand its occurrence within the definitive host. Key words: disease ecology, habitat, infection risk, parasite transmission, wildlife disease, wetlands. INTRODUCTION Although pathogen prevalence is often summarized across large spatial scales, local heterogeneity in infection patterns can reveal valuable insights about epidemiological processes. Spatial patterns of infection can be used to identify environmental risk factors, examine parasite ecology, and investi- gate the role of landscape composition on disease dynamics (Ostfeld et al. 2005). Spatial variation in the likelihood of acquiring infections can be caused by a variety of host behaviours and environmental factors. Social behaviour, territoriality and habitat selection can impact contact rates among hosts and the dispersion of fecal material in the environment, which has implications for the epidemiology of pathogens with both direct and fecal–oral trans- mission routes (Altizer et al. 2003). However, the importance of environmental factors is most evident in the case of indirectly transmitted para- sites. The relationship between environmental factors and parasite dynamics has been repeatedly demonstrated in a variety of pathogens where successful transmission is dependent on vectors, intermediate hosts or the survival of free-living stages outside the host (Thomson et al. 2000; Ostfeld et al. 2005; Pickles et al. 2013). Thus, hypotheses about how pathogens spread through populations can be investigated by quantifying infection patterns against a backdrop of environ- mental variation at local, regional and global scales. Meningeal worm (Parelaphostrongylus tenuis) and giant liver flukes (Fascioloides magna) are both para- sites with complex life cycles that primarily infect ungulates of the family Cervidae (Lankester and Samuel, 1998). In North America, the definitive host for both parasites is the white-tailed deer (Odocoileus virginianus), and both require an inter- mediate gastropod host to complete their life cycles. Parelaphostrongylus tenuis is a protostrongy- lid nematode that infects a host’s nervous tissue in the spinal cord and the venous sinuses and subdural space in the cranium (Lankester and Samuel, 1998). First-stage larvae (L1) are passed in the feces of infected deer and are subsequently taken up by ter- restrial gastropods. Within the gastropod, the larvae develop into their third-stage (L3), which are infective to deer. Deer become infected by ingesting infected gastropods (Fig. 1A, Lankester and Samuel, 1998). * Corresponding author. Department of Veterinary Population Medicine, University of Minnesota, 1365 Gortner Avenue, St. Paul, Minnesota 55108, USA. E-mail: kvw@umn.edu 1 Parasitology, Page 1 of 13. © Cambridge University Press 2014 doi:10.1017/S0031182014001802