Dallas, Tad, Alyssa-Lois M. Gehman, A. Alonso Aguirre, Sarah A. Budischak, John M. Drake, Maxwell J. Farrell, Ria Ghai, Shan Huang, and Ignacio Morales-Castilla. “Contrasting Latitudinal Gradients of Body Size in Helminth Parasites and Their Hosts.” Global Ecology and Biogeography, vol. 28, issue 6, 2019, pp. 804-813.
Aim: We examined body size scaling relationships for two developmental life stages of parasitic helminths (egg and adult) separately in relationship to latitude (i.e. Bergmann's rule), temperature and temperature seasonality. Given that helminth eggs experience environmental conditions more directly, whereas adults live inside infected host individuals, we predict stronger environmentally driven gradients of body size for eggs than for adults. Location: Global. Time period: Present day. Major taxa studied: Parasitic helminths. Methods: We compiled egg size and adult body size data (both minimum and maximum) for 265 parasitic helminth species from the literature, along with species latitudinal distribution information using an extensive global helminth occurrence database. We then examined how the average helminth egg and adult body size of all helminth species present (minimum and maximum separately) scaled with latitude, temperature and temperature variability, using generalized linear models. Results: Both the egg size and the adult body size of helminths tended to decrease towards higher latitudes, although we found the opposite body size scaling pattern for their host species. Helminth sizes were also positively correlated with temperature and negatively, but more weakly, with temperature seasonality. Main conclusions: Instead of following the body size patterns of their hosts, helminth parasites are more similar to other ectotherms in that they follow the converse Bergmann's rule. This pattern did not differ between helminth developmental stages, suggesting that mean annual temperature and seasonality are unlikely to be related mechanistically to body size variation in this case.
Ezenwa, Vanessa O., Anna E. Jolles, Brianna R. Beechler, Sarah A. Budischak, and Erin E. Gorsich. “The Causes and Consequences of Parasite Interactions: African Buffalo as a Case.” Wildlife Disease Ecology: Linking Theory to Data and Application, edited by Kenneth Wilson, Andy Fenton, and Dan Tompkins. Cambridge University Press, 2019, pp. 129-160
Gehman, Alyssa-Lois M., Dara A. Satterfield, Carolyn L. Keogh, Alexa Fritzsche McKay, and Sarah A. Budischak. “To Improve Ecological Understanding, Collect Infection Data.” Ecosphere, vol. 10, issue 6, e02770.
Abstract: Ecologists seek to understand and predict how organisms respond to multiple interacting biotic and abiotic influences, an increasingly difficult task under anthropogenic change. Parasites are one of these biotic influences that are pervasive in natural systems and frequently interact with other stressors. Because they often have cryptic effects on their host organisms, their role in the distribution, abundance, composition, and dynamics of populations, communities, and ecosystems is easy to overlook. However, studies that neglect the role of parasitism may miss or misinterpret organismal responses to environmental change, hampering ecological predictions. We discuss case studies wherein the inclusion of parasite infection status altered the interpretation of ecological outcomes, and offer paths forward to make parasite data acquisition, analysis, and interpretation more accessible to ecologists. Given that parasites are responsive to environmental changes, timely attention to their influence on host responses is critical for accurately predicting future ecological states.
van Leeuwen, Anieke, Sarah A. Budischak, Andrea L. Graham, and Clayton E. Cressler. “Parasite Resource Manipulation Drives Bimodal Variation in Infection Duration.” Proceedings of the Royal Society B, vol. 286, issue 1902, 2019, 20190456.
Abstract: Over a billion people on earth are infected with helminth parasites and show remarkable variation in parasite burden and chronicity. These parasite distributions are captured well by classic statistics, such as the negative binomial distribution. But the within-host processes underlying this variation are not well understood. In this study, we explain variation in macroparasitic infection outcomes on the basis of resource flows within hosts. Resource flows realize the interactions between parasites and host immunity and metabolism. When host metabolism is modulated by parasites, we find a positive feedback of parasites on their own resources. While this positive feedback results in parasites improving their resource availability at high burdens, giving rise to chronic infections, it also results in a threshold biomass required for parasites to establish in the host, giving rise to acute infections when biomass fails to clear the threshold. Our finding of chronic and acute outcomes in bistability contrasts with class theory, yet is congruent with the variation in helminth burdens observed in human and wildlife populations.
External Grant: National Science Foundation, Division of Environmental Biology- Ecology of Infectious Diseases. “Habitat and Coinfection as Drivers of Heterogeneity in Cross-Scale Wildlife Infectious Disease Processes.” Principal Investigator: Kristian Forbes. Co-Principal Investigators: Clayton Cressler, Richard Hall, and Sarah Budischak. Award #1911925, June 15, 2019-June 30, 2024.
Abstract: In order to predict and control the spread of infectious diseases, it is important to understand the role of "superspreaders". These are hosts who transmit disease more often than most other infected individuals. To understand superspreaders this project will investigate how immunity to infections, host diet, and whether or not the host is infected with other parasites creates variation among individuals in susceptibility to pathogens and the ability to transmit infections. To do so, this project will develop mathematical frameworks of virus spread, to predict how food resources and infection with a parasite will first shape the risk that an individual will become infected, and then, will shape the spread of disease across populations and landscapes. These predictions will be tested using laboratory and field experiments with bank voles infected with Puumala hantavirus. The results of this project will shed new light on why some individuals become superspreaders and others do not. This has relevance to improving surveillance and management of this hantavirus, which regularly spills over from its vole reservoir host to infect humans, as well to other pathogens of concern to human and agricultural health. The project will also support the training of high school science teachers from across the United States, providing them with a hands-on research experience in Finland. This will equip them with activities and materials to use to teach high school students about the importance of emerging infectious diseases. This research will examine the individual and synergistic effects of habitat quality and helminth coinfection on wild bank voles infected with the zoonotic pathogen, Puumala hantavirus. The project will develop novel mathematical theory to mechanistically link diet and coinfection with pathogen transmission to predict how bottom-up (diet-driven) and top-down (coinfection-driven) processes interact to drive the emergence of superspreaders, and how this individual-level variation scales up to influence pathogen transmission at the population- and landscape-level. These predictions will be tested using both laboratory vole infection experiments and powerful manipulative experiments involving supplemental feeding and de-worming treatments of wild vole populations in forests. By concurrently developing mathematical models and integrating them with empirical data, this project will quantify how habitat and coinfection influence (1) individual host competence for microparasite infection, (2) demographic and contact processes governing local transmission and (3) dispersal rates and landscape attributes that determine spatial spread of disease.