Toward a mechanistic understanding of helminth coinfections: Disentangling the within- and between-host processes of infection and the role of climate
Restricted (Penn State Only)
- Author:
- Vanalli, Chiara
- Graduate Program:
- Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 01, 2023
- Committee Members:
- Matthew Ferrari, Chair of Committee
Isabella Cattadori, Major Field Member & Dissertation Advisor
Peter Hudson, Major Field Member
Jessica Conway, Outside Unit & Field Member
Marino Gatto, Special Member
Elizabeth Mcgraw, Program Head/Chair - Keywords:
- Gastrointestinal helminths
Antibody attack rate
Cross-immunity
Free-living stages
Seasonality
Temperature
Humidity
Spatial distribution - Abstract:
- The dynamics of infectious diseases are driven by processes that occur across multiple scales. Within the host, the immune response regulates the intensity and duration of parasite infections and protects from subsequent re-infections, albeit not always successfully. Host immunity against a parasite can be altered by the presence of a second parasite species and immune-mediated competition, facilitation or neutralism are each possible outcomes of parasite-parasite interactions. Within-host interactions between coinfecting parasites can generate a cascade of effects that can modify parasite transmission and persistence in a host population. Furthermore, natural host-parasite systems are constantly under the effect of environmental forces, which add an additional layer of complexity to the drivers of infection and transmission. Climatic variables directly affect the abundance of parasites in the environment, and have been found to impact infection seasonality, geographical distribution and size of outbreaks. The study of the impacts of global warming on infectious diseases is particularly relevant for predicting climate change effects on the wellbeing of populations and planning adequate interventions. Despite efforts toward more effective treatments and control strategies, infectious diseases remain a global issue for public health, agriculture, and wildlife conservation, with consequences that could be worse under global warming. A more holistic vision is needed to understand how the different processes occurring across scales concomitantly affect parasite infection, which can provide key insights into reducing disease burden. The development and implementation of mechanistic models represents a useful approach for disentangling the contribution of the multiple drivers that affect infection dynamics and for comparing processes across host-parasite systems. These models can provide testable hypotheses on the relative contribution of different mechanisms and offer relevant knowledge to improve our current understanding of the processes that drive parasite transmission and persistence. In my dissertation, I use soil-transmitted helminths to investigate the interactions between immunological, epidemiological and environmental drivers of single and coinfections, and to foresee their consequences at both the within-host and epidemiological scales. Using data from the lab on parasite intensity and immune response, I identify an immune-mediated interaction between two coinfecting helminths of the European rabbit. General immunological findings are confirmed by field data on two natural rabbit populations from Scotland, where coinfection leads to increased parasite intensity, higher parasite shedding and longer survival in the environment. In addition, I investigate the non-linearities in the climatic response of free-living stages of different helminth species, providing projections of future spatiotemporal dynamics of the hazard of helminth infection under a changing climate. Overall, my research work enhances our mechanistic understanding of the complex interactions between the multiple drivers of helminth infections and how these dynamics are altered in the presence of coinfections. My findings provide insights on processes occurring across different scales and offer a more realistic representation of the dynamics of a host-parasite system using both lab and field data. Ultimately, the within-host, immune-epidemiological and climate-driven mathematical frameworks I have developed are useful tools to investigate similar research questions in other host-parasite systems, including livestock and human infections that share similar challenges.