Publications

A review of pathogens, diseases, and contaminants of muskrats (2020)

Figure 1. U.S. states and Canadian provinces that muskrat (Ondatra zibethicus) health surveys have been conducted in North America for (A) viruses, (B) bacteria, (C) protozoan parasites, (D) trematodes, (E) cestodes, (F) nematodes, (G) ectoparasites, and (H) toxins and contaminants. Locations designated by shaded regions.

​Abstract: Over the last 50 years, significant muskrat (Ondatra zibethicus) harvest declines have been observed throughout North America. Several theories for the decline have been proposed, including increased parasite infections and disease within muskrat populations. No existing wholistic review of muskrat exposure to pathogens, contaminants, and diseases exists. To address this knowledge gap, we conducted a thorough review of existing literature on muskrat pathogens, contaminants, and diseases across their natural range. This review is comprised of 131 articles from 1915 to 2019 and from 27 U.S. states and 9 Canadian provinces. A wide diversity of contaminants, toxins, and pathogens were reported in muskrats, with the most common diseases being cysticercosis, tularemia, Tyzzer's disease, and biotoxin poisoning from cyanobacteria. This review provides a summary of muskrat pathogens, contaminants, and diseases over a century that has observed significant population declines throughout the species' range in North America. Such data provide a baseline for understanding the potential role of disease in these declines. In addition, these data highlight critical knowledge gaps that warrant future research efforts.

Citation: Ganoe, L.S., J.D. Brown, M.J. Lovallo, M.J. Yabsley, M.G. Ruder, W.D. Walter. 2020. A review of pathogens, diseases, and contaminants of muskrats (Ondatra zibethicus) in North America. Frontiers in Veterinary Science, 7:233. doi:10.3389/fvets.2020.00233  

Ecology of an isolated muskrat population during regional population decline (2021)

Fig 2. Comparison of all 4 (kernel density estimator [KDE]href, KDEad hoc, KDEplug-in, and local convex hull [LoCoH]) estimators of home range for the 95% and 50% isopleths for 2 individual Ondatra zibethicus (Muskrat) from August 2018 to February 2019. The pond–stream matrix in Lewisburg, PA, is depicted by the gray-shaded areas and labeled as water features.

Abstract: Evidence indicating a decline in Ondatra zibethicus (Muskrat) populations in the United States during the past 40 years has led to speculation regarding factors influencing Muskrat survival. In order to understand population dynamics and survival, it is important to first define the ecology of local populations. We investigated the dwelling structure use, movements, home range, and survival of radio-tagged Muskrats (n = 14) in an urban wetland complex in central Pennsylvania. We used locations collected from intensive radio-telemetry monitoring to determine number of lodging structures used, hourly movement, and size and percent area overlap of home ranges. Muskrats shared an average of 9 lodging structures, and on average, 68% of a Muskrat's home range overlapped home ranges of other Muskrats. We used 4 home-range estimators (kernel density estimator [KDE]href, KDEad hoc, KDEplug-in, and local convex hull estimator) to assess the ability of each estimator to represent Muskrat home ranges. The KDEplug-in that constrained the estimate of home range to habitat boundaries provided the most appropriate home-range size for Muskrats in a linear–non-linear habitat matrix. We also calculated overwinter survival estimates using known-fate models. Our top model indicated a positive effect of the average weekly precipitation on survival, with an overwinter survival estimate of 0.59 (SE = 0.16). The main cause of Muskrat mortality was predation by Neovison vison (American Mink; n = 6). The small sample size and uncertainty surrounding our model selection led to weak estimates of survival; however, our model suggests that snowfall may be an important factor in Muskrat survival. Our study provides novel data on Muskrat ecology in Pennsylvania as well as preliminary evidence for future investigations of factors affecting Muskrat survival during the winter months.

Citation:​ Ganoe, L.S., M.J. Lovallo, J.D. Brown, D.R. Diefenbach, W.D. Walter. 2021. Ecology of an isolated muskrat (Ondatra zibethicus) population during regional population decline. Northeastern Naturalist, 28(1): 49-64. https://doi.org/10.1656/045.028.0104​

Surveillance for diseases, pathogens, and toxicants of muskrat in Pennsylvania (2021)

Fig 4. Distribution of female muskrat (Ondatra zibethicus) carcass weight (kg) with respect to the presence or absence of placental scars in Pennsylvania, USA, 2018–2019. Mean weight for each group is indicated by dashed lines.

Fig 6. Prevalence of intestinal helminths (Pprev), cysts (Cprev), Clostridium piliforme, and Toxoplasma gondii in muskrats (Ondatra zibethicus) by region (NW-Northwest, SW-Southwest, NC-Northcentral, SC-Southcentral, NE-Northeast, SE-Southeast) in Pennsylvania, USA, 2018–2019. * = P < 0.001, ** = 0.001 < P < 0.05.

Fig 8. Graphical representation of a Bayesian censored analysis of covariance model depicting relationships between muskrat (Ondatra zibethicus) carcass weight (kg) and heavy metal concentrations (ppm, wet weight) for each sex.

Abstract: Using diagnostic data and contemporary sampling efforts, we conducted surveillance for a diversity of pathogens, toxicants, and diseases of muskrats (Ondatra zibethicus). Between 1977 and 2019, 26 diagnostic cases were examined from Kansas and throughout the Southeast and Mid-Atlantic, USA. We identified multiple causes of mortality in muskrats, but trauma (8/26), Tyzzer’s disease (5/6), and cysticercosis (5/26) were the most common. We also conducted necropsies, during November 2018—January 2019 Pennsylvania muskrat trapping season, on 380 trapper-harvested muskrat carcasses after the pelt was removed. Tissue samples and exudate were tested for presence of or exposure to a suite of pathogens and contaminants. Gastrointestinal tracts were examined for helminths. Intestinal helminths were present in 39.2% of necropsied muskrats, with Hymenolepis spp. (62%) and echinostome spp. (44%) being the most common Molecular testing identified a low prevalence of infection with Clostridium piliforme in the feces and Sarcocystis spp. in the heart. We detected a low seroprevalence to Toxoplasma gondii (1/380). No muskrats were positive for Francisella tularensis or Babesia spp. Cysticercosis was detected in 20% (5/26) of diagnostic cases and 15% (57/380) of our trapper-harvested muskrats. Toxic concentrations of arsenic, cadmium, lead, or mercury were not detected in tested liver samples. Copper, molybdenum, and zinc concentrations were detected at acceptable levels comparative to previous studies. Parasite intensity and abundance were typical of historic reports; however, younger muskrats had higher intensity of infection than older muskrats which is contradictory to what has been previously reported. A diversity of pathogens and contaminants have been reported from muskrats, but the associated disease impacts are poorly understood. Our data are consistent with historic reports and highlight the wide range of parasites, pathogens and contaminants harbored by muskrats in Pennsylvania. The data collected are a critical component in assessing overall muskrat health and serve as a basis for understanding the impacts of disease on recent muskrat population declines.

Citation: Ganoe, L.S., J.D. Brown, M.J. Lovallo, M.J. Yabsley, M.G. Ruder, W.D. Walter. 2021. Surveillance for diseases, pathogens, and toxicants of muskrat (Ondatra zibethicus) in Pennsylvania and surrounding regions. PLoS ONE 16(12): e0260987. https://doi.org/10.1371/journal.pone.0260987

Fatal infection with Versteria sp. in a muskrat (2021)

Figures 1–4. Systemic Versteria sp. infection in a muskrat (Ondatra zibethica). Figure 1. Dozens of tapeworm cysts in the liver. Figure 2. Tapeworm cysts throughout the lungs. Figure 3. In the liver, the cysts effaced the parenchyma and contained polycephalic tapeworm larvae covered by a thin capsule/bladder cell (arrow). H&E. Figure 4. In the liver, the rostellum of 1 scolex containing 2 rows of short hooks (arrow) and adjacent sucker (arrowhead) characteristic of Versteria sp. H&E

Abstract: The Taeniidae tapeworms are a family of helminths that have a similar life cycle, with intermediate hosts developing characteristic cysts in visceral organs. We describe here a case in Pennsylvania, USA, of fatal Versteria infection in a muskrat (Ondatra zibethicus), which, to our knowledge, has not been reported to develop disease associated with infection. Postmortem examination revealed widespread tissue loss and replacement by solid-bodied cestode larvae with minimal adjacent inflammation in many visceral organs, most severe in the lungs, liver, and brain. Key morphologic features via histology included cephalic structures and short rostellar hooklets, which are characteristic for the genus. Genetic characterization confirmed the cestode as being an undescribed lineage of Versteria that has been implicated as the cause of severe morbidity and mortality in humans and nonhuman primates in North America. Considering the zoonotic significance of this pathogen, our report expands on the limited literature regarding disease caused by Versteria and emphasizes the need to identify the causative tapeworm more accurately, especially in rodent intermediate hosts given that previous reports do not have molecular confirmation of species.

Citation: Niedringhaus, K.D., L.S. Ganoe, M.J. Lovallo, W.D. Walter, M.J. Yabsley, J.D. Brown. Fatal infection with Versteria sp. in a muskrat, with implications for human health. Journal of Veterinary Diagnostic Investigation. December 2021. doi:10.1177/10406387211064270

Transient persistence of bobcat occurrence throughout a human‐dominated landscape (2022)

Fig 4: Predictive maps of the (a) probability of occupancy at equilibrium of colonization and extirpation, (b) probability of site-level colonization ( γ ), (c) detection probability for a survey at a site (p), and (d) probability of site-level turnover from one season to the next. The maximum estimated probabilities were 0.87 for occupancy, 1.00 for colonization, 0.91 for detection, and 0.27 for site-turnover [Color figure can be viewed at wileyonlinelibrary.com]

Citation: Mayer A.E., T.J. McGreevy Jr, C. Brown, L.S. Ganoe, B.D. Gerber (2022). Transient persistence of bobcat (Lynx rufus) occurrence throughout a human-dominated landscape. Population Ecology, 1:13. doi:10.1002/1438-390X.12123 10.1002/1438-390X.12123

Abstract: Human developments have detrimental effects on wildlife populations globally with carnivores being particularly sensitive. The bobcat (Lynx rufus) is often considered an adaptable mesocarnivore that occurs throughout varied landcover types within its wide distribution and may be less susceptible to the negative effects of development. Our objectives were to investigate the landscape occupancy dynamics of bobcats in a highly developed and densely populated region of the northeastern United States to evaluate the sensitivity of bobcat occurrence to natural and anthropogenic landscape features. We established a large-scale camera trapping survey throughout Rhode Island, USA, sampling from 2018 to 2020. Using dynamic occupancy models, we found initial site occupancy was positively influenced by the amount of forested wetland habitat, while increasing road density and shrub cover negatively influenced the probability of site colonization. Surprisingly, we found no hypothesized variables to influence site-level extirpation probability, or any seasonal effects on dynamic parameters. Lastly, we found that forest cover and road density negatively influenced the probability of detection. The probability of occupancy was high, >0.8, throughout much of the study area (49%), but we also found relatively high site transients, with the probability a site would change occurrence status from season to season at ≈0.27 in the majority of the study area (70%). Our results show that although bobcats can persist in human-dominated landscapes, they require contiguous natural areas to do so. Future expansion of road infrastructure may reduce habitat connectivity and increase road mortalities, thus jeopardizing the population.

News and Outreach Articles

​Ganoe, L.S. “Look, mom! Is that a muskrat?”. Linn Log fall newsletter of the Merrill W. Linn Land & Waterways Conservancy, Lewisburg, PA.

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