This project will develop a mechanistic understanding of marine transmission of the protozoal parasite Toxoplasma gondii. The team will investigate the role of marine aggregates in the transport of T. gondii and other zoonotic pathogens. An oceanography-based transport model will be coupled to epidemiological data to evaluate if T. gondii infection in sea otters can be predicted by the distribution of aggregate-associated and unattached T. gondii oocysts from terrestrial versus marine sources. The scientists will also investigate whether sea lions are definitive hosts capable of releasing infectious oocysts (current literature indicates that only felines can serve as definitive hosts).
The project will represent a significant advance towards understanding an important parasite, which infects both terrestrial and marine animals. The research will also improve our comprehension of the role marine aggregates play on disease transmission and explore if sea lions are definitive hosts for T. gondii. The team has extensive experience in the area and this research will build upon their previous findings on the transport of T. gondii from land to sea.
The broader impacts of this project are very strong. The PI has strong record of student training and educational outreach. Three undergraduates, three graduate students and three post-doctoral researchers will be trained and mentored during the conduct of this important project. The study will provide outreach to K-8 students, water resources managers and ocean enthusiasts via public websites, benefiting sea otter recovery and management policies. The scientists will contribute to exhibitions at the Farallones National Marine Sanctuary.
This project was unique in its multidisciplinary and comprehensive ‘One Health’ approach – integrating marine ecologists, oceanographers, epidemiologists, molecular biologists, modelers, and parasitologists to investigate the ecology of zoonotic pathogens in the marine environment. Our goal was to develop a mechanistic understanding of the marine transmission dynamics of Toxoplasma gondii, an important cause of parasitic disease in marine mammals, particularly Southern sea otters (Photo 1), and humans. We investigated a novel paradigm and showed that although California sea lions (Photo 2) shed T. gondii-like oocysts in their feces, these oocysts were molecularly distinct, previously unrecognized coccidian parasites. Therefore, evidence to date confirms that wild and domestic felids are the only known definitive hosts of T. gondii. Our molecular surveillance of 959 wild-caught mussels demonstrated higher than previously reported T. gondii contamination of California coastlines as well as novel strains of the parasite (Photo 3). Epidemiological field investigations coupled with laboratory transport experiments showed that the distribution of oocysts in marine habitats is a function of oocyst loading from domestic and wild felids via freshwater run-off (Photo 4: Coastal freshwater run-off) and oocyst transport dynamics that are governed by association with aggregates (marine snow) and sticky polymers. Particle aggregation affects both the spatial distribution and bioavailability of oocysts to invertebrates that can serve as a source of infection for marine mammals and potentially humans. In addition to being incorporated in aggregates, T. gondii (and potentially other pathogens) adhere to sticky polysaccharides, called excreted polymeric substances (EPS) that enhance their association with sinking aggregates and incorporation into biofilms (Photo 5). Gelatinous polymers including EPS are fundamental to biophysical processes in aquatic habitats, including mediating aggregation processes and functioning as the matrix of biofilms. The ramifications of our findings extend the role of aquatic polymers in oceanic processes and show that invisible colloids, biofilms and food webs play an important role in disease ecology in marine environments. We further demonstrated that EPS facilitate the acquisition, concentration, and retention of T. gondii by kelp-grazing snails, which can transmit T. gondii to threatened southern sea otters. Freshwater sources that may transport pathogens to coastal waters are often delivered to piers, coral reefs, kelp beds, and tide pools – habitats known to contain rich EPS-producing biota. Thus, coastal waters that receive contaminated runoff may also contain high levels of polymers that could mediate critical disease transmission mechanisms, including the spatial distribution and fate of terrestrial pathogens in nearshore habitats. Finally, our refined understanding of T. gondii oocyst transport dynamics facilitated an unprecedented modeling effort that links space-time patterns in pathogen distributions and otter movement, yielding a mechanism-based estimate of otter disease risk that can be compared with epidemiologically established risk patterns. This achievement will aid future research and relevant stake holders by making more accurate projections of how disease risk may change due to alterations in watershed pollutant loading, climate variability, land use, estuarine habitat quality, kelp forest dynamics, and coastal ocean circulation. Overall, findings from this project benefit the threatened southern sea otter population, which is struggling to recover, as well as other marine mammals and humans sharing the coastal environment. Training and outreach were strongly emphasized in this project involving 5 PhD, 1 Masters, and 5 undergraduate students, as well as 4 post-docs. Our research provided the basis for e-learning case modules that were employed by project Co-PIs in a new hybrid undergraduate ‘Fundamentals of One Health’ course, launched in 2013, which inspired the development of a new undergraduate Major/Minor in Global Disease Biology at UC Davis. This Major is led by NSF-EEID-funded PIs with the intent to encourage a better understanding of the interconnectedness of human, animal and plant disease ecology. Our research and sea otter information will continue to be available through the Karen C. Dryer Wildlife Health Center website (www.vetmed.ucdavis.edu/whc/). Our research on environmental pathogen pollution was integrated into exhibits and curriculum programs developed in collaboration with the Gulf of the Farallones National Marine Sanctuary. Students and post-docs in our project were active participants in outreach at community, national and international scientific meetings as well as programs at 86 different K-12 schools throughout California, working with 106 teachers to directly engage 4192 students in interactive lessons and games we developed based on our coastal research. (Photo 6). Informational bookmarks that we produced and distributed to students to share with their families increased the overall outreach of our educational information to approximately 10,000. A key outreach objective of our NSF project was thus achieved by training enthusiastic and effective science communicators and leaders to better inform the public and regularly engage them to understand the value of science and our research.
