Movement potential of infectious prions by American crows (Corvus brachyrhynchos) in an area endemic for chronic wasting disease.
Open Access
- Author:
- Walters, Tyler
- Graduate Program:
- Ecology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- August 07, 2024
- Committee Members:
- W. David Walter, Thesis Advisor/Co-Advisor
Frances E Buderman, Committee Member
Jason Kaye, Program Head/Chair
C. Guilherme Becker, Committee Member - Keywords:
- American crow
RT-QuIC
Chronic wasting disease
Corvus brachyrhynchos
Home range - Abstract:
- American crows (Corvus brachyrhynchos) can be found throughout much of North America and are known to play a role in the ecology of multiple diseases including West Nile virus (Orthoflavivirus nilense), Campylobacter jejuni, Escherichia coli, Avipoxvirus, antibiotic resistant bacteria, and Collyriclum faba. Laboratory experiments have also shown the potential for crows to pass infectious prions in their feces after being gavaged with infected meat, however, this has not yet been documented in a wild setting. Collecting fecal and cloacal samples from wild crows for diagnostic purposes and studying the space use and resource selection of crows will contribute to better understanding of their potential role in the movement of infectious prions such as those associated with chronic wasting disease (CWD). Chronic wasting disease is a transmissible spongiform encephalopathy that is caused by infectious prions and is known to affect cervids such as white-tailed deer (Odocoileus virginianus), mule deer (Odocoileus hemionus), elk (Cervus canadensis), moose (Alces alces), red deer (Cervus elaphus), and reindeer (Rangifer tarandus). Since the discovery of CWD there have been several methods developed to diagnose individuals with the disease. Initially the diagnostic tools available could only be utilized for samples collected postmortem (e.g., retropharyngeal lymph nodes, obex). Continued research and development resulted in the expansion of the available diagnostic tools and the specimen types which can be tested. There were several different early diagnostic tests used to detect the presence of prions and these assays each have their own strengths and weaknesses in terms of cost, time to complete, specificity of results, and level of expertise required to interpret. Immunohistochemistry (IHC) is one methodology used for the detection of prions that involves fixing thin slices of tissue, treating with an antibody stain that binds to prions, with subsequent viewing under a microscope for interpretation. The IHC does not require amplification, but results can be subjective as they depend on an interpretation by an experienced, certified pathologist. Amplification of the prions within a sample enables the use of additional diagnostic assays. Protein misfolding cyclic amplification (PMCA) increases the concentration of prions within a sample if they are present by utilizing repeated cycles of protein replication within a substrate and exposure to ultrasound to break down polymers and encourage more replication. Enzyme linked immunosorbent assay (ELISA) involves treatment with proteinase to remove normal prion and then combines the amplified sample material in a solution with monoclonal antibodies. Light absorbency of the solution is measured after a period of incubation to indicate the presence or absence of abnormal prions in the final step of an ELISA. The amplified material can also be tested using western blot which requires sodium dodecyl-sulfate polyacrylamide gel electrophoresis, nitrocellulose sheets, electrophoretic transfer, and treatment with antibodies to produce a radioautograph for interpretation. The IHC, ELISA, and western blot assays that indicate positive results identifies the prions present in a sample are specific to CWD. These diagnostic tools have been critical in the detection of CWD in wild and captive cervids and surveillance efforts to monitor and understand the geographical spread of the disease. These diagnostic tools are unable to quantify the level of prions present within a sample or their potential disease transmission risk to another individual. Bioassays can be utilized to determine if a given sample and method of exposure result in disease transmission. For a bioassay to be effective the animal receiving the sample must be a species that is naturally susceptible to the infectious agent, or a transgenic animal bred to be susceptible. Mule deer, white-tailed deer, and swine (Sus domesticus) are all naturally susceptible. Transgenic mice and Syrian hamsters (Mesocricetus auratus) have been bred to be susceptible and are used for bioassays. There are multiple routes of inoculation that have been used in bioassays for CWD, including, but not limited to, intracranial injection, intravenous injection, intraperitoneal injection, aerosolized inoculation, intra-nasal inoculation, and oral inoculation. Although amplified materials are useful for diagnostic purposes, if the goal of a given bioassay is to replicate a natural encounter it is important that the samples being used are a homogenate of non-amplified materials. There is continued development in the types of samples and protocols that can be used to detect CWD with a focus on antemortem testing option of effected species. In addition, testing samples from species including coyotes (Canis latrans), raccoons (Procyon lotor), and opossums (Didelphis virginianus) has been conducted because they share the landscape with susceptible species and to investigate their roles in the landscape ecology of infectious prions. We investigated the diagnostic capability of a new method of prion detection, real time quaking induced conversion assays (RT-QuIC), for fecal and cloacal swab samples of wild crows to detect the presence of infectious prions. In total, 61 samples were tested for the presence of infectious prions using RT-QuIC, including both samples from American crows and fish crows (Corvus ossifragus). Although reactivity that resulted in increased fluorescent reading was observed for multiple samples using RT-QuIC there was no conclusive evidence that infectious prions were present. Understanding the way in which crows move across the landscape and their resource selection will also help inform our understanding of the role crows may play. We captured 15 American crows and outfitted them with global positioning system (GPS) transmitters to record locations (n=53,521) along with multiple home range estimators to calculate home range size estimates for individuals by season. We found a high level of variability for 95% home range estimates between individual crows ranging from 0.76 km2 to 346.7 km2. Covariates representing habitat type, potential resource rich locations, and landscape features were incorporated into integrated step selection functions and Akaike’s Information Criteria was used to determine the model of best fit for each individual. The most common model of best fit across individuals and seasons consisted of distance to waste, distance to water, and elevation. We found that some individual crows do interact with captive cervid facilities and carcass dump bins which may result in exposure to infectious materials. Crows were also documented crossing the established regulatory boundaries of disease management areas showing a potential mechanism of infectious material being transferred across these boundaries. The small home range size of most individuals; however, may minimize the likelihood of long distance spread of CWD by crows.