Wildlife Disease and Toxicology I

Contributed Paper
ROOM: Room 130 – Cimarron

1:10PM Raccoon Roundworm Intensity Distributions across Hosts and Modeled Implications for Population Management
Matthew E. Gompper; Aniruddha Belsare; Harith Al-Warid
Raccoon roundworm (Baylisascaris procyonis) is a nematode parasite whose definitive host is the raccoon (Procyon lotor). While its impacts on raccoons are generally negligible, the lifecycle of B. procyonis potentially involves a broad array of paratenic vertebrate hosts including humans, domestic animals, and diverse wildlife species. In infected paratenic individuals the impacts of the parasite may be severe, resulting in significant risk of morbidity and mortality, which may amplify to population-scale effects. Mitigating such impacts may require managing raccoons, but how to do so remains unclear. One such approach is the culling of raccoons. Problematically, based on data from Arkansas and Missouri (prevalence = 44%), the distribution of intensity of the parasite among hosts is strongly skewed such that only a small proportion (20%) of hosts harbor the majority (90%) of nematodes. Such patterns are common among macroparasites, and have significant management implications. We use a series of modeling approaches to show that non-selective culling (that is, host removal without replacement), especially culling that fails to target a large proportion of the host populations, is likely to miss the rarer heavily infected hosts. As a result, prevalence and mean intensity has the potential to increase following non-selective culling. An alternative approach is to use anti-helminthic baits to target nematodes without culling hosts (parasite removal without replacement). Such approaches can reduce prevalence, but whether the component population intensity is reduced is a function of reaching a threshold coverage of treatment, as most baits are likely to be consumed by hosts with no or minimal infections.
1:30PM The Potential of Fish to Act as Transport Hosts for Dracunculus Medinensis and D. Insignis Larvae.
Christopher A. Cleveland; Mark L. Eberhardt; Alec Thompson; Stephen J. Smith; Hubert Zirimwabagabo; Robert Bringolf; Michael J. Yabsley
The pattern of dog infections in Chad, Africa with Dracunculus medinensis (Guinea worm) suggests a paratenic host may be involved. Previous work on fish suggested that they are either resistant to infection or have variable species susceptibility. Our objective was to evaluate the potential role of fish to serve as transport hosts of D. medinensis and D. insignis by exposing fish to Dracunculus-infected copepods and then feeding them to domestic ferrets. Two of three ferrets fed fish that had ingested D. insignis-infected copepods became infected. Transmission of D. medinensis also occurred when a ferret ingested fish that had ingested infected copepods. The infection of ferrets with both Dracunculus spp. after consumption of fish illustrates a novel experimental transmission route, highlighting the importance of current recommendations to cook fish thoroughly, bury entrails, and prevent dogs from consuming fish and fish entrails in an effort to decrease the potential transmission of guinea worm.
1:50PM Adapting a Determinants of Health Model to Identify Drivers and Priorities for Salmon Population Health in Two Groups of Experts
Julie Wittrock; Colleen Duncan; Craig Stephen
Salmon health features prominently as a policy and management goal in literature and Canadian legislation but without clear guidance on what constitutes health apart from numbers of fish returning and absence of specific diseases. Our objective was to develop and test the feasibility of a determinants of health approach for identifying the drivers of health in Pacific salmon (Oncorhyncus spp.). A population health model including social, biological, and ecological factors was adapted to Pacific salmon. A diagrammatic network analysis was conducted to summarize expert opinion on the relative importance and direction of effect of the determinants of health identified in a literature-based model. This method was employed in two groups of experts, with Fisheries and Oceans Canada-Pacific Science staff (n=11) and with representatives of the First Nation Fisheries Council (n=13). The resulting networks represent the relationships mentioned by two or more experts. Both expert groups identified the six thematic determinants of health in their networks. While the First Nations Fisheries Council participants delineated more relationships (47 edges) than the Fisheries and Oceans Canada participants (31 edges), both networks emphasized the importance of habitat quality as a driver of salmon population health. The model is adaptable and scalable to different contexts. It provides a unifying framework and candidate salmon health metrics to focus discussion on health policy priorities in a consistent and transparent manner. This conceptual health model could be adapted to specific populations by providing a standardized format for review and assessment. The approach allowed for a visual means to develop a collective view of the important drivers of health for this population. The model could be used as a mechanism to foster dialogue and shared visioning for salmon health goals and priorities.
2:10PM Size Matters: Sample Size Calculations for Harvest-Based Wildlife Disease Surveillance Using an Agent-Based Framework
Aniruddha V. Belsare; Matthew E. Gompper; Joshua J. Millspaugh
Epidemiological surveillance for important wildlife diseases mostly relies on samples obtained from hunter-harvested animals. Though this is a convenient and cost-effective strategy, samples so obtained may not be representative of the population primarily due to sampling biases associated with harvest and heterogeneities associated with the spatiotemporal distribution of a disease in the population. Surveillance outcomes would be misleading if unrealistic assumptions underpin sampling design or analysis of sample data. We have developed a model-based framework that incorporates sampling biases and disease distribution heterogeneities, and provides population-specific recommendations for collection and analysis of disease surveillance data obtained from hunter-harvested animals (or other non-probabilistic sampling methods). Application of this agent-based framework is illustrated using the example of chronic wasting disease (CWD) surveillance in white-tailed deer (Odocoileus virginianus) population of Franklin County in eastern Missouri. We show that unrealistic assumptions result in underestimation of sample sizes required for efficient detection of CWD (≥ 95% detection probability) for a range of detection thresholds. Reliance on suboptimal sample sizes will affect the sustainability and efficiency of CWD surveillance strategy due to misleading inferences about the occurrence of CWD in a population. Our model-based framework can be used by wildlife agencies to guide collection and analysis of surveillance data that relies on non-probabilistic methods like harvest-based sampling, and adapt their CWD surveillance strategy for efficiency as well as sustainability. The framework can be readily adapted for other disease systems and used for informed-decision making while planning and implementing disease surveillance in wild and free-ranging species.
2:30PM Prevalence and Distribution of Amphibian Pathogens and Parasites in North Dakota
Melanie Firkins; Vasyl Tkach; Robert Newman
Disease is one of the most frequently cited factors associated with amphibian declines. Three sources of disease have been most commonly noted: chytrid fungus, Ranavirus, and some helminth parasites. Our objective was to estimate the distribution and prevalence of these agents in amphibians across the state of North Dakota. We also tested for associations between disease and helminth occurrence and general ecological factors. We sampled broadly across the state, including all major ecoregions and land use categories and obtained a total of 705 amphibians of six species. We used real time PCR assays for Ranavirus and chytrid, and morphological and molecular techniques to identify helminths. We found Ranavirus in adult amphibians to be common and widespread across the state, with a prevalence of 35.6%. Ranavirus varied significantly by species (higher in toads), ecoregion, and land use. Geographically, infected individuals were encountered throughout the state, with at least one infection detected at 55.9% of locations. Ranavirus occurrence was greater in the Missouri Coteau than other ecoregions, but was spatially-structured at a finer scale. Chytrid was rarely detected (0.007%), possibly because of extreme dry conditions in the year prior to our study. All chytrid infections were found in central North Dakota. In contrast, helminths were commonly found. The majority of amphibians were infected with digeneans (60.3%), followed by nematodes (17.4%), with cestodes much less common (2.8%). Parasite species varied in their distribution across the state, with some showing a fine-scale patchy distribution. More comprehensive surveys and long-term monitoring need to be implemented to provide a more complete understanding of parasite distributions and ecological associations, and most importantly, temporal dynamics such as disease outbreaks and their causes, including interactions with environmental stressors such as climatic conditions and habitat quality.
2:50PM Refreshment Break
3:20PM Transmission of Influenza a Virus from Mallards to European Starlings Via Shared Water
Susan Shriner; Katherine L. Dirsmith; Jeremy W. Ellis; J. Jeffrey Root; Kevin T. Bentler; Nicole L. Mooers; Loredana McCurdy
Influenza A viruses (IAVs) have the potential to cause serious economic harm to poultry and when highly pathogenic strains emerge they may be problematic if they spill back into wildlife. While mallards (Anas platyrhynchos) are a very common reservoir host for IAVs, these birds are infrequently found on farms. Therefore, we are studying bridge hosts for IAVs, which are hosts that come into contact with both maintenance hosts (aquatic birds) and/or their habitats and poultry and/or their environment. In this study, we assessed the susceptibility of European starlings (Sturnus vulgaris) to a low pathogenic IAV by experimentally inoculating starlings with a North American H4N6 virus. We then evaluated the transmission of IAV from experimentally infected mallards via a shared water source. We inoculated three mallards in a pen that shared water with three other pens, each of which housed three starlings and then repeated this experiment three times. For the experimental inoculation and transmission replicates, we collected oral, cloacal, and fecal swabs daily and then tested the swabs for viral RNA using qPCR. All ten experimentally inoculated starlings became infected with a mean peak in oral shedding of 104.09 EID50/mL on the first day post inoculation. In the transmission experiments, all starlings (N = 9 per replicate) became infected in each of the three replicates. Peak oral shedding varied from 103.38 EID50/mL to 103.51 EID50/mL and transmission was evident in different individuals between days three and seven post inoculation of the mallards. In all three replicates, the viral RNA load in the water peaked at around 104 EID50/mL. This study demonstrates that starlings can be infected with low pathogenic IAV from water contaminated by infected mallards. Accordingly, starlings should be considered in the development of farm biosecurity plans in order to minimize the potential risk of IAV transmission to poultry.
3:40PM Effects of Sub-Acute External Exposure to Deepwater Horizon Oil in the Double-Crested Cormorant
Brian S. Dorr; Katie C. Hanson-Dorr; Katherine Healy; Katherine Horak; Karen M. Dean; Steven J. Bursian; Kendal Harr; Jane E. Link
The Deepwater Horizon (DWH) oil spill presented new challenges in how oil spills affect the environment including that oil dispersed from 70 km offshore and the active spill continued for several months, resulting in potential for repeated sub-acute exposure of wildlife to oil. We evaluated physiological effects in Double-crested Cormorants (Phalacrocorax auritus) externally exposed (n=13) repeatedly to sub-acute levels (13 g/exposure) of artificially weathered DWH petroleum crude oil compared to control birds (n=12). Hematologic values, thermography, body weight, and internal body temperature data were collected across multiple time points and compared using linear mixed effects regression models with a repeated measures structure. Organ weights and tissue were collected at necropsy. Sub-acute external exposure to oil resulted in hemolytic anemia associated with development of Heinz bodies and reduced packed cell volume. Over the study period, we found that WBC, monocyte, and lymphocyte counts were significantly greater (p < 0.05) in oiled birds. At necropsy, we documented gross abnormalities in the hearts of oiled birds. Absolute and relative liver, kidney, and gastrointestinal track weight was greater (p < 0.05) in treated cormorants, with evidence of associated oxidative damage to both liver and kidney tissues. Internal body temperatures were stable over the course of the study period for both control and treated cormorants; however, infra-red thermal images of oiled cormorants indicated significantly (p < 0.05) greater surface temperatures that resulted in greater heat loss in treated cormorants. Increased energetic demand to maintain internal body temperature was compensated through observed increased food consumption in oiled birds. Both oiled and unoiled groups maintained or gained weight during the study period. In this study, repeated exposure to sub-acute levels of DWH oil resulted in multiple negative physiological impacts to cormorants.
4:00PM Variation in SAα2,3-Gal is Linked to Variation of Avian Influenza Viral Shedding in Mallard Ducks
Amanda C. Dolinski; Jen C. Owen
Mallards (Anas platyrhynchos) are an important natural host for low path avian influenza viruses (LPAIV). Within a population there is extreme variation in the amount of virus shed by individuals, with 20% of the population accounting for 80% of the shed virus. LPAIV largely replicates in the intestinal tract of these ducks by attaching to α-2,3-galactose (SAα2,3-Gal) linked receptors located on the surface of host intestinal epithelial cells. The objective of this study was to determine if variation in abundance of SAα2,3-Gal in duodenum, jejunum, ileum, cecum, colon, and bursa of Fabricius corresponds to observed variation in viral shedding. Wild mallard eggs (n=70) were collected from uncultivated fields in Northeastern North Dakota, then hatched and raised in captivity. At 2-3 months of age they were orally infected with LPAIV H5N9 (n = 60) or sham-inoculated (n=10). Viral shedding was assessed via cloacal swabs collected at different time points post infection. Ducks (n= 10-15) were sacrificed at 1, 2, 5, 15, and 29 days post infection (DPI). Sections of duodenum, jejunum, ileum, cecum, colon, and bursa of Fabricius were collected for histological examination of SAα2,3Gal using lectin histochemistry (Maackia amurensis agglutinin I). Using Image-J we quantified the concentration of SAα2,3Gal by lectin staining of each tissue type. Mallards exhibit marked variation in SAα2,3Gal concentration throughout the intestines, while the bursa remained relatively consistent. Further, the concentration of receptors is positively correlated with the total virus shed by individual birds, which suggests that more SAα2,3Gal in the intestines of mallards corresponds to more virus shed. While we cannot establish cause and effect, a better understanding of the inherent variation in SAα2,3-Gal could be the key to understanding the variation in viral shedding by individuals within a population.
4:20PM West Nile Virus Prevalence in Sympatric Populations of Greater Sage-Grouse and Culex tarsalis
Lindsey A. Bischoff; Travis Runia; Andrew Gregory; Jonathan A. Jenks
The Greater Sage-Grouse (Centrocercus urophasianus) is a species of conservation concern and is highly susceptible to mortality from West Nile virus (WNv). WNv first appeared in the United States in 1999. The virus exists in a bird mosquito bird cycle and despite being a known source of mortality for sage-grouse, individuals are able to survive, at low rates. Culex tarsalis is the suspected primary vector for transmitting WNv to sage-grouse. To determine the WNv prevalence in sage-grouse in South Dakota, we collected blood from 95 individuals in 2016 that were either captured or hunter harvested. We used a plaque reduction neutralization assay to test serum for WNv antibody titers. We captured and fitted female sage-grouse with VHF radio-transmitters and monitored their survival daily during peak WNv season (June 15 September 15). Deceased birds with recoverable tissue were sent to the laboratory and tested for active WNv. We trapped mosquitoes with CO₂-light traps four nights per week (252 trap nights) to detect the presence of WNv on the landscape. One male and one female sage-grouse contained antibodies (2.1% of total, 1.9% of females, 2.4% of males). None of the 11 sage-grouse that died during WNv season tested positive for active WNv. We captured 6,696 mosquitoes of which 1,809 were Culex tarsalis. We documented six WNv detections in Culex tarsalis. Detections occurred from 20 July to 14 September 2016. Estimated WNv prevalence for 2016 in Culex tarsalis was 0.3%-7.6%. These results suggest that WNv was not a significant source of sage-grouse mortality in South Dakota during 2016. However, we still need to assess the interactions between WNv and habitat quality. South Dakota is an ideal place to study WNv habitat interactions since it is the fringe of the sage-grouse range, resulting in a variety of habitat qualities.
4:40PM Potential of Fish Eating Birds to Spread Virulent Aeromonas Hydrophila
Fred L. Cunningham; Katie Hanson-Dorr; Lorelei Ford; Alex Crain; Lanna Durst; Raleigh Middleton; Larry Hanson
Aeromonas hydrophila is a Gram-negative, rod shaped, facultative anaerobic bacterium that is ubiquitous to freshwater and slightly brackish aquatic environments and can cause infections in fish, humans, reptiles and avian species. Recent severe outbreaks of disease in commercial catfish aquaculture ponds have been associated with a highly virulent Aeromonas hydrophila strain (VAh) that is genetically distinct from less virulent strains. This strain is responsible for over 3 million pounds of catfish losses per year. Previous research has shown that Great Egrets, Double-crested Cormorants (Phalacrocorax auritus), American White Pelicans (Pelecanus erythrorhynchos), and Wood Storks (Mycteria americana) can carry and shed viable VAh after consuming fish infected with VAh. These fish-eating birds can serve as a reservoir for VAh and may spread the pathogen while foraging on uninfected catfish ponds. Therefore, our objectives were to 1. Examine the role of fish-eating birds in the epidemiology and spread of VAh, 2. Evaluate the potential and likely process for colonization of VAh in non- endemic catfish ponds by evaluating transmission using a piscivorous bird (Great Egret, Arde alba) model in experimental ponds. We found that VAh survives passing through the GI tract of Great Egrets and viable VAh can be shed at substantial levels for a limited period when birds consume infected fish. We found that both treatment ponds had positive qPCR results for VAh while the control pond remained negative. VAh was detected in fish, pond water, chironomids, invertebrates, snails and mud from treatment ponds. We conclude that fish eating birds that consume fish infected with VAh can spread the bacteria to naïve ponds and cause a disease outbreak.


Contributed Paper
Location: Albuquerque Convention Center Date: September 24, 2017 Time: 1:10 pm - 5:00 pm