Cryptosporidium and Giardia are important disease agents for both humans and animals worldwide. Unlike many pathogens, their capacity for surviving in soil and water for extended periods of time enables environmental transmission. Both parasites replicate within warm-blooded vertebrate hosts and are excreted as an environmentally resistant oocyst or cyst, respectively. New hosts become infected through ingestion of oocysts or cysts in contaminated water, food, or soil. The objective of this thesis work was to utilize an epidemiologic approach to identify environmental factors associated with the prevalence of Cryptosporidium and Giardia spp. in California coastal wetlands, as well as to ascertain the prevalence and identify potential transmission pathways within the animal community in the Virunga Massif, Rwanda.
Because Cryptosporidium and Giardia are waterborne parasites, key factors in wetland ecology were examined for their impact on parasite levels in water. First, concentrations of these parasites within three coastal California wetlands were determined. Proximity to livestock operations and recent rainfall events were associated with increased pathogen levels. Second, experimental models mimicking wetland characteristics were used to isolate the effects of several parameters. Vertical settling columns identified increased salinity as leading to slower settling of Giardia and horizontal flow mesocosm tanks identified increased salinity as leading to slower removal of Cryptosporidium. Furthermore, presence of vegetation led to enhanced removal of Cryptosporidium oocysts, Giardia cysts, and Toxoplasma gondii surrogates from surface water in the mesocosm tanks.
The impact of Cryptosporidium and Giardia on animal health is important not only because many wildlife species are suspected to be reservoirs of these parasites for humans, but also because the effect of infection with these parasites on health is of concern in vulnerable wildlife species. To assess the impact of these parasites on mountain gorillas (Gorilla beringei beringei), a critically endangered primate restricted to two forests located in Rwanda, Democratic Republic of Congo and Uganda, an investigation was conducted comparing protozoal prevalence and strain identity in mountain gorillas, domestic cattle, and forest buffalo (Syncerus caffer nanus). Giardia was found in all three species, and genotyping results identified genotypic assemblage B in the gorilla samples and assemblage E in the cattle samples. While this study did not confirm a transmission pathway between cattle and gorillas using the forest buffalo as an intermediary, it suggests that future work should also evaluate humans as potentially contributing to fecal pathogen contamination within the forest.
Environmentally transmitted protozoa are of global health concern due to their extended survival outside of a host, coupled with the relative difficulty and expense of detection in environmental samples. The drivers for protozoal disease transmission, as detailed in Chapter 1, emphasize the key role that environmental change has on Giardia and Cryptosporidium. Some of these changes are evaluated in Chapters 2 and 3, which highlight research conducted on protozoal transport through coastal wetlands. Health impacts of these protozoa on wildlife and livestock cannot be discounted and Chapter 4 surveys the presence of Cryptosporidium and Giardia in a complex wildlife community in Rwanda.
