Wildlife Disease and Toxicology


  • Reduced Organo-Somatic Indices in Biota Exposed to Lead-Contaminated Sediment Suggests Pathological Changes to the Spleen and Hepatopancreas
  • Michelle Seers; Katrina Knott
    Lead (Pb) is a pervasive heavy metal implicated in a wide spectrum of toxic effects including metabolic disturbances, impaired hematopoiesis and anemia in fish and wildlife. We hypothesized that organisms exposed to high doses of Pb would exhibit signs of organ cytotoxicity such as cellular necrosis and an elevated inflammatory response. To test this hypothesis, we examined the organo-somatic indices (OSI) of fish from three rivers in southeast Missouri (Big River, Flat River, Meramec River) that have been impacted by historic mining and contain a gradient of elevated in-stream sediment concentrations of Pb (50-1200 mg/kg dry weight). OSI of fish from the Castor River (sediment Pb < 20 mg/kg dry weight) were used as reference. Spleen and hepatopancreas OSI were calculated as (organ mass/total body mass) * 100 for three species of fish (Lepomis megalotis, Moxostoma erythrurum, and Ambloplites rupestris).
    OSI for the spleen (mean ± SD; 0.097 + 0.059 %) and hepatopancreas (0.652 + 0.155 %) of Lepomis megalotis from contaminated sites were lower than the reference site (0.134 + 0.046 % and 1.016 + 0.243 %, respectively) and hence indicative of necrosis. OSI for other species were limited to fewer sites and the relationship to Pb exposure was unclear. Variation due to site-specific Pb concentrations, fish age and duration of exposure should be considered. Tissue damage suspected by differences in OSI among sites will be confirmed with histopathological assessment. The relationships between OSI and Pb concentration in fish fillets and blood are currently under investigation.
    Decreasing OSI in response to Pb exposure could serve as an early indicator of mortality, poor body condition, and impaired reproduction in fish populations. Knowledge of the adverse effects of Pb on fish and wildlife should be considered in habitat management decisions and regulatory recommendations to effectively preserve sustainable populations.

  • Examining Relationships between Testosterone and Parasite Loads in Southern Flying Squirrels*
  • Katherine Rexroad; Dr. Christopher Jacques; Seán Jenkins
    Male biased parasitism is attributed to differences in body size, space use, or hormone levels. Hormone levels may influence parasite loads, and impact long-term fitness of wildlife. Unique aspects of flying squirrel ecology in our study region, such as, female biased size dimorphism and lack of intersexual differences in space use, makes them good model organisms to study the effects of hormones on immunity. Therefore, we predicted that immunosuppressive effects of testosterone may contribute to increased parasite loads in male SFS. During spring 2019, we captured and collected fecal samples from 32 SFS in western Illinois. We quantified testosterone using an enzyme-linked immunosorbent assay. Parasites were counted and identified using a fecal sedimentation technique and microscopy. Thirty-one of 32 SFS were infected with ≥1 species of endoparasites, including coccidia (n=28), Strongyloides robustus (n= 21), and pinworms (n=11). Our analyses revealed no differences in parasite loads (W = 114, P> 0.9) between male (x̄= 60, SE = 35) and female (x̄ = 62, SE = 23) SFS. Similarly, we did not find a relationship between testosterone levels and parasite loads (F (1,15)= 0.39, P = 0.54, R2 = 0.04). To date, our results do not directly support the hypothesis that testosterone is immunosuppressive in SFS inhabiting fragmented Midwestern landscapes, though previous investigations suggest potential associations between space use and parasite infection in relation to habitat fragmentation. Thus, continued testing of potential effects of testosterone on SFS parasite loads may provide greater insight into the synergistic interactions of hormones and endoparasites of SFS, which may aid in future conservation of SFS in fragmented habitats.

  • The Short Straw: Insectivorous Bat Exposure to Microplastics*
  • Ashleigh B. Cable; Emma V. Willcox
    Bats in temperate North America are experiencing precipitous population declines due to habitat loss and degradation, wind turbine mortality, and disease. Environmental contaminants may affect fitness and elevate the impacts of other stressors to bats. Microplastics are emerging environmental contaminants and can be detrimental to wildlife health. These tiny plastic particles can be transferred from aquatic to terrestrial systems via emergent aquatic insects; thus, bioaccumulation of microplastics is a concern for aerial insectivores that prey on thousands of insects a night. Our objectives are to 1) determine the extent of microplastic exposure and accumulation in bats and 2) investigate pathways of microplastic exposure related to diet. Using bat carcasses collected from rabies and wind farm monitoring programs, we will use a chemical digestion method to isolate plastic particles from tissues and a dissecting microscope to describe the shape and size of these particles. We will then use a spectroscopy method to characterize the chemical properties of the particles. By testing a variety of tissue types from bat carcasses, we will determine the extent of microplastic accumulation in different internal tissues. By assessing plastics in guano collected when mist netting, we will also determine concentrations and types of plastic particles that successfully exit the body. To investigate diet as a pathway of exposure, we will also use guano pellets for genetic diet analysis to identify prey consumed. We will use the data we collect to investigate relationships between prey consumed and attributes of plastic particles (i.e., size, shape, concentration and chemical property). Our findings will improve understanding of bat exposure to microplastics, the potential for microplastics to affect bat fitness, and the need for remediation strategies to limit bat exposure to microplastics.

  • Emerging Viral Diseases in At-Risk Populations of Felids and Ungulates*
  • Natalie R. Payne; Melanie Culver; Koenraad Van Doorslaer
    Introduction: Sonoran felids (bobcats (Lynx rufus), pumas (Puma concolor), jaguars (Panthera onca), and ocelots (Leopardus pardalis)) and ungulates, including the Sonoran pronghorn (Antilocapra americana sonoriensis), may be threatened by the emergence of new viruses associated with climate change and habitat encroachment. The ocelot, jaguar, and pronghorn are endangered in the region and likely to be at increased risk of susceptibility to emerging diseases due to decreased genetic variation. Additionally, individuals from the recovering Florida panther population have recently been observed presenting with a neuromuscular disorder (feline leukomyelopathy) of unknown cause. Objectives: The objectives of this study are to integrate population genomics and viromics for the Florida panther and five Sonoran species: puma, bobcat, ocelot, jaguar, and pronghorn. Additionally, novel viruses and viruses most likely to pose threats to population viability from disease outbreaks will be identified. Identification of potential viral etiologic agents of feline leukomyelopathy will also be attempted. Methods: Population structure and connectivity, genetic diversity, and inbreeding will be determined through ddRAD-Seq, and viromes will be characterized using a metagenomic approach. Paired samples (scat with buccal swabs or muscle tissue) will be used to assess the reliability of using scat samples to identify viruses for which species of interest, rather than prey items, are the hosts. Results: Viromic and phylogenetic analyses of viral DNA sequences from puma and bobcat scats from Mexico suggest the presence of a novel circovirus in these populations. Conclusions: The novel circovirus may represent the first known feline circovirus, although further comparisons between sample types are required to resolve if the viral host is felid. Circoviruses are known to cause life-threatening illness in other mammals, so these results may have important implications for Sonoran felid health. These findings may inform management decisions to supplement populations by translocation and take preventative measures, such as vaccine administration.

  • Impact of Gastrointestinal Parasites on Gut-Hormone-Immune Relationships in Wild Howler Monkeys*
  • Kathryn M. Benavidez; Michael D. Wasserman
    Humans and nonhuman animals are hosts to a wide range of microorganisms which correspond to aspects of physiology, ancestry, and ontogeny. Highly diverse gut microbial communities provide physiological benefits, such as aiding in digestion and reduced risk of gastrointestinal disorders. Research within microbial endocrinology has unveiled direct interactions between gut microbes and the neuroendocrine system, and these interactions correlate closely with parasite susceptibility. Thus, I plan to test the following two hypotheses: [H1] howler monkeys (Alouatta palliata) will have specific hormone-immune profiles associated with gut microbial community composition and [H2] howler monkeys will have gut microbe-hormone-immune profiles that correspond to the presence of gastrointestinal parasites. Objectives for testing these hypotheses include to: [1] use genetic methods to measure helminth diversity and microbial diversity in feces, and [2] use immunoassays to measure glucocorticoids and immunoglobulin A (IgA) in feces. Overall, I expect that howler monkeys with higher parasites loads will have increased glucocorticoids, decreased IgA, and decreased microbial diversity. I previously collected samples from wild howler monkeys at Barro Colorado Island, Panama. I followed a randomly chosen howler group each day for six days a week and collected fecal samples (n = 88). Upon collecting samples, I determined the sex and age-class of the individual. To measure microbial diversity, I extracted RNA and performed high throughput sequencing of the 16S rRNA gene. Next, I extracted DNA and plan to use this material to identify the presence of helminth species. Enzyme immunoassays will be used to measure IgA levels and glucocorticoids. To my knowledge, this is the first research to investigate the gut-endocrine-immune interactions in wild primates. Utilizing an interdisciplinary approach that integrates frameworks and toolsets from primatology, microbial ecology, endocrinology, and parasitology offers novel insights for understanding primate biology and conservation.

  • Sounders of Alarm: The Role of Feral Swine in the Eco-Epidemiology of Tick-Borne Diseases in the Southeastern United States
  • Brent Clayton Newman
    Feral swine (Sus scrofa) occur in 38 US states with an estimated population size of at least 6 million individuals. As an invasive alien species, they pose a significant threat to native ecological communities, agriculture, and veterinary public health. However, their role as hosts for hematophagous arthropods and circulating of arboviral diseases in the United States is not well understood. Therefore, we collected ticks (Ixodidae) from 54 hunter-killed feral swine from May through August 2016-2019 in the William B. Bankhead National Forest, Alabama, US. Our objectives were to identify tick-feral swine host association(s) and determine presence of tick-borne pathogens in ticks obtained from feral swine via molecular assays. A total of 885 ticks representing three species were collected: 626 adult (268 female and 358 male), 141 nymph Lone star (Amblyomma americanum), 101 adult (35 female and 66 male) American dog (Dermacentor variabilis), and 17 adult (7 female and 10 male) Gulf Coast (Amblyomma maculatum) ticks. Pathogen testing of ticks confirmed the presence of Ehrlichia chaffeensis in ~12% and 7% of adult and nymph lone star ticks, respectively, and ~6% and 17% of adult American dog and Gulf Coast ticks, respectively. Rickettsia species was detected from all 3 species at both nymph and adult life stage. All ticks were RT-PCR negative for Heartland Virus. Our results indicate that invasive feral swine not only support three endemic tick species but also may serve as reservoir and/or amplifying host for multiple tick-borne pathogens of veterinary public health concern in the southeastern United States.

  • Interspecific Oral Rabies Vaccine Bait Competition in the Southeast United States
  • Wesley Cole Dixon
    The epizootic of rabies in raccoons (Procyon lotor) and its public health impacts during the 1980’s in the Eastern U.S. sparked an interest in controlling the disease at the landscape scale with oral rabies vaccination (ORV). By 2005, the USDA had implemented a cooperative raccoon rabies control program using ORV to establish a strategic vaccination zone targeting raccoons to prevent the spread of raccoon rabies west of the Appalachians. This program successfully contained the spread of the epizootic and the current management objective is to eliminate raccoon rabies from the United States. However, consumption of vaccine baits by non-target species can reduce bait availability for raccoons reducing the number of animals vaccinated and the effectiveness of the ORV program. Previous studies in the Midwest have revealed that Virginia opossums (Didelphis virginiana) are a major bait competitor in agricultural landscapes. Additional information on interspecific ORV bait competition in the Southeastern United States is warranted to improve science-based decision making relative to vaccine bait distribution. To characterize the community of species competing with raccoons for ORV baits, we constructed twelve grids each containing twelve motion-sensing cameras during August to December 2019 in two forest types along the Savannah River near Aiken, South Carolina. The cameras were baited with placebo ORV baits and images were analyzed to identify all species consuming baits. Based on 21,600 camera nights of data, our results revealed a diverse community of bait competitors including wild pig (Sus scrofa), grey fox (Urocyan cineroargenteus), coyote (Canis latrans) and Virginia opossum. More unexpectedly was the impact of invertebrates on bait consumption. Specifically, we found in some bottomland hardwood grids fire ants (Solenopsis invicta) were responsible for over 90% of baits consumed. We discuss the implications of non-target bait competition on rabies control and elimination of raccoon rabies in the Southeastern US.

  • Exposure to infectious agents in dogs in Matsigenka community at Manu National Park, Peru: possible sentinels of diseases in wildlife and humans
  • Miryam Jeanette Quevedo Urday; Jesus Christian Onofre Lescano Gomez; Guillermo Salvatierra; Oscar Mujica; Juvenal Silva
    Manu National Park (MNP) is an Amazonian Protected Natural Area located in Madre de Dios region, Peru. Park buffer zones have intermixtures among humans, domestic animals, and wildlife, a rich environment for exchanging pathogens. This study aimed to assess the exposure of domestic dogs to the following zoonotic agents: Leptospira spp., Dirofilaria immitis, Ehrlichia canis, and Anaplasma phagocitophylum. Samples were collected from all dogs (N=26) kept at three Matsigenka native communities within MNP. Microagglutination test (MAT) was used for detecting antibodies against nine serogroups of Leptospira spp., whereas all other agents were diagnosed using a commercial ELISA test. Seropositive frequency (and 95% CI) was calculated for each agent. Moreover, association between seropositive frequency and the community of origin was evaluated using the Fisher Exact test (α=0.05). Antibodies against at least one of the assessed Leptospira serogroups were detected in 92.3% (24/26; 95%CI 75.9 – 97.9%). All evaluated serogroups (9/9) were found in at least one sample. Tayakome and Yomibato communities presented the highest frequencies (100%) of antibodies against Leptospira spp. The most frequently detected serogroups were Canicola (65.4%), Tarassovi (61.5%), and Georgia (53.8%). A significant association (p<0.05) was found between the frequency of seropositive dogs and the community. D. immitis antigen was detected in 53.8% (14/26; 95% CI 35.5 – 71.3%) of evaluated samples. Frequencies of seropositive dogs were 83%, 40%, and 22% for the communities of Tayakome, Maizal, and Yomibato, respectively. A significant association (p<0.05) between seropositivity and the community was observed. These results suggest native communities living at MNP might be exposed to some infectious agents which should be considered within public health programs focused on this population.


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