Abstract

The protozoan parasites Cryptosporidium and Giardia spp., as well as the bacteria Salmonella and Campylobacter spp., are shed in the feces and are well-recognized causes of gastrointestinal disease in animals and humans. The fecal bacteria Vibrio cholerae, Clostridium perfringens, and Plesiomonas shigelloides can also cause disease under the right combinations of microbe, host, and environmental factors. All of these pathogens can be spread directly by fecal-oral transmission or indirectly by fecal contamination of water and food supplies. In California, there is evidence of significant fecal pathogen pollution flowing from terrestrial to aquatic ecosystems and animals along the coast. To develop ecosystem monitoring and management strategies, we tested the hypothesis that fecal pathogens are detectable in nearshore filter feeding bivalves and in terrestrial storm runoff collected from fecal-impacted coastal ecosystems in California. In addition to evaluating bivalve shellfish as bioindicators of fecal pollution in aquatic ecosystems, a goal of this research was to identify risk factors for detecting fecal pathogens in bivalves and storm runoff during the three year study.

The bivalve field studies tested 4800 mussels (Mytilus spp.) and 600 clams (Corbicula spp.) from marine, estuarine, and riverine ecosystems along the California coast for Cryptosporidium spp. Genotypes detected in bivalves included the anthropozoonotic C. parvum genotype 2, as well as the host specific C. andersoni and C. felis that are shed by cattle and cats, respectively. In addition, 2 novel Cryptosporidium genotypes were detected in mussels. A subset of the bivalve samples was also tested for Giardia, Salmonella, Campylobacter, V. cholerae, C. perfringens, and P. shigelloides. All of these microbes were detected in bivalves except for Campylobacter spp. Risk factors associated with detecting fecal pathogens in freshwater clams included wet season sampling and downstream location. Region and sewage management practices were not significant predictors of fecal pathogen detection in outplanted riverine clams. Risk factors associated with fecal pathogen detection in estuarine and marine mussels included exposure to freshwater outflow and precipitation in the week preceding mussel collection. The fecal risk classification of mussel collection sites, the water type, and the bivalve type were not significant predictors for detecting fecal pathogens in mussels along the California coast.

The storm runoff study evaluated the distribution of Cryptosporidium on coastal dairies and the efficacy of various farm management practices to reduce the load of Cryptosporidium oocysts in storm runoff. Risk factors associated with detection of Cryptosporidium and Giardia in storm runoff included cattle age, total seasonal precipitation, and water turbidity. Calves were found to be important loading sources of Cryptosporidium on the farms, and Best Management Practices (BMPs) such as vegetative buffer strips were found to effectively reduce the load of oocysts and cysts in storm runoff. In conclusion, a variety of pathogenic parasites and bacteria were detected in storm runoff and filter feeding invertebrates, suggesting that fecal pollution is common in coastal ecosystems of California and that Best Management Practices may be useful in reducing the load of fecal pathogens flowing from terrestrial to aquatic ecosystems.