Gnotobiotic Pig Models for the Study of Enteric Pathogen Replication and Pathogenesis
| dc.contributor.author | Nyblade, Charlotte June | en |
| dc.contributor.committeechair | Yuan, Lijuan | en |
| dc.contributor.committeemember | Auguste, A. Jonathan | en |
| dc.contributor.committeemember | Duggal, Nisha K. | en |
| dc.contributor.committeemember | Kehn-Hall, Kylene | en |
| dc.contributor.committeemember | Meng, Xiang-Jin | en |
| dc.date.accessioned | 2024-10-31T14:37:25Z | en |
| dc.date.available | 2024-10-31T14:37:25Z | en |
| dc.date.issued | 2024-10-09 | en |
| dc.description.abstract | Clostridioides difficile (C. difficile) and human rotavirus (HRV) are leading causes of bacterial and viral gastroenteritis worldwide. Treatment and vaccination options for both pathogens have significant limitations. C. difficile infections are treated with antibiotics, which is paradoxical as C. difficile itself is associated with antibiotic usage. In the United States, two live oral attenuated vaccines (Rotarix and RotaTeq) are licensed for protection against HRV. Since receiving approval from the World Health Organization (WHO), Rotarix and RotaTeq have been widely implemented into global national childhood immunization schedules, with one report finding 59 countries using Rotarix and 25 using RotaTeq. However, these vaccines have much lower efficacy rates in low- and middle-income countries. Because of these caveats, there is an urgent need to generate novel prophylaxes and treatments for C. difficile and HRV. In order to address this need, animal models that replicate the nuances of each infection are imperative. We have developed gnotobiotic (Gn) pig models for each pathogen. Gn pigs infected with spores of the hypervirulent UK1 strain of C. difficile develop classical signs of infection, including watery diarrhea and weight loss. Gross necropsy reveals colonic distention and discoloration, and histopathological evaluation shows volcano lesions, pseudo membrane formation, and epithelial cell erosion. Gn pigs infected with a G4P[6] strain of HRV also display pathogen specific signs of infection, including diarrhea, fecal rotavirus shedding, and damaged intestinal villi. A dose response study of the G4P[6] strain revealed diarrhea and virus shedding occurred at all tested doses, however the most severe diarrhea and virus shedding, measured by cumulative diarrhea score, area under the curve (AUC) of diarrhea, peak virus titer, and AUC of virus shedding, were all detected in the highest dose group. Based on the presentation of clinical signs of infection, 105 fluorescent focus units was selected as the optimal challenge dose for future studies. These models enable us to test candidate therapeutics, but also elucidate unique replicative features of the pathogens. For example, we found that HRV can replicate in the salivary glands and nasal cavity of Gn pigs in addition to the small intestine. HRV infection primed immune responses in the ileum, tonsils, and facial lymph nodes; infection also induced high levels of systemic and mucosal rotavirus specific antibody responses. Moving forward, we hope to expand upon this replication study to identify what cell types within the glands are infected as well as look at local cellular immune responses to HRV infection. Additional future directions include determining the protective efficacy of next generation HRV vaccines and evaluating effectiveness of an engineered probiotic yeast in reducing severity of C. difficile infection and disease. The Gn pig models of C. difficile and G4P[6] HRV are clinically relevant, and they will continue to serve as useful tools to better our understanding of pathogenesis, infection, and prevention of these pathogens. | en |
| dc.description.abstractgeneral | Clostridioides difficile (C. difficile) and human rotavirus (HRV) both cause gastrointestinal related symptoms when they infect humans. Treatments available for C. difficile and HRV all have significant drawbacks. This represents a gap in knowledge which we aimed to fill by developing germ-free (gnotobiotic [Gn]) pig models of C. difficile and HRV infection and disease. Animal models that mimic the outcomes of disease seen in humans are essential for evaluating protectiveness of new therapeutics. The more similar the disease presentation, the more likely the treatment results will be translational to humans. We began with C. difficile; pigs were orally fed C. difficile and monitored for a week post infection for development of signs of infection. Inoculated pigs lost weight and developed diarrhea. Bacterial cells and toxins were isolated from fecal samples collected on various days post infection. Multiple changes were observed in infected pigs’ large intestinal tissues, including severe bleeding, tissue distension, and fluid buildup. Infected pigs also had significant upregulation of pro-inflammatory cytokines, indicating activation of the immune response. We performed a similar procedure for the establishment of the HRV model. Gn pigs were orally challenged with differing doses of G4P[6] HRV and followed for several days post infection. Consistent with HRV infection in children, the pigs developed watery diarrhea that lasted for multiple days. Small intestinal tissues collected at necropsy had several signs of damage, including blunted villi, fluid buildup, and immune cell invasion. These lesions were also consistent with HRV infection in humans. Taken all together, these results indicated successful establishment of both C. difficile and HRV models. While the primary goal of generating these models was to evaluate new treatments, a secondary goal was to use them to better our understanding of pathogen replication dynamics. For example, the small intestine was thought to be the primary site of HRV infection. Using a pig model of HRV, we expanded on this knowledge to show that HRV can replicate in the nose and salivary glands as well. Additionally, we found HRV infection to induce immune responses near the sites of infection, including the intestine, the tonsils, and the facial lymph nodes. Overall, these studies demonstrate the utility of germ-free pig models and are an important first step in generating more effective treatments for bacterial and viral infections. | en |
| dc.description.degree | Doctor of Philosophy | en |
| dc.format.medium | ETD | en |
| dc.format.mimetype | application/pdf | en |
| dc.identifier.uri | https://hdl.handle.net/10919/121514 | en |
| dc.language.iso | en | en |
| dc.publisher | Virginia Tech | en |
| dc.rights | In Copyright | en |
| dc.rights.uri | http://rightsstatements.org/vocab/InC/1.0/ | en |
| dc.subject | Clostridioides difficile | en |
| dc.subject | human rotavirus | en |
| dc.subject | gnotobiotic pigs | en |
| dc.title | Gnotobiotic Pig Models for the Study of Enteric Pathogen Replication and Pathogenesis | en |
| dc.type | Dissertation | en |
| dc.type.dcmitype | Text | en |
| thesis.degree.discipline | Biomedical and Veterinary Sciences | en |
| thesis.degree.grantor | Virginia Polytechnic Institute and State University | en |
| thesis.degree.level | doctoral | en |
| thesis.degree.name | Doctor of Philosophy | en |