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The development and implementation of a method using blue mussels (Mytilus spp.) as biosentinels of Cryptosporidium spp. and Toxoplasma gondii contamination in marine aquatic environments
Significance and Impact to Agency needs and mission: • This research directly supports the Clean Water Act, specifically with regards to “the protection and propagation of fish, shellfish, and wildlife, and recreation in and on the water, where attainable” (Section 101(a)(2) and Section 303(c)(2)(A)). • This study provides additional drivers for increasing the Agency’s focus on T. gondii as a clear human health threat with regards to improving current water quality standards that protect our water resources for safe drinking, recreation, and shellfish propagation practices. • The research done for this product has also advanced research efforts in the Agency to provide occurrence methods for regulated and unregulated parasites that are now being used in other parts of the RAP, including stormwater research (SSWR 5.2 E), other products in SSWR 2.2 B, and SSWR 5.2G.2. It is important to note that the use of shellfish as “sentinels” water quality has been used for the last 20 years, by NOAA, as part of their Mussel Watch Program to monitor for chemical contaminants throughout the US. The key findings reported in this study lays the ground work for now using indigenous or “transplanted” biosentinels (e.g., shellfish) as continuous microbial water quality monitoring devices in various watersheds throughout the United States.
It is estimated that protozoan parasites still account for greater than one third of waterborne disease outbreaks reported. Methods used to monitor microbial contamination typically involve collecting discrete samples at specific time-points and analyzing for a single contaminant. While informative, many of these methods suffer from poor recovery rates and only provide a snapshot of the microbial load at the time of collection. Bivalves have been proposed as a natural filtration alternative as they are more efficient and can simultaneously concentrate and retain parasites, bacteria, and viruses for an extended period of time. In this study, we examined the use of indigenous California blue mussels (Mytilus spp.) as biosentinels to monitor for the occurrence of Toxoplasma gondii and Cryptosporidium spp. in marine waters. We describe the development of a method to extract oocyst DNA from mussel hemolymph, gills, and digestive gland tissues followed by PCR-based detection of these pathogens. Results showed that this method was able to consistently detect as few as 10 oocysts. A survey of indigenous mussels from Point Lobos and Morro Bay, California, areas known to have high T. gondii seroprevalence in sea otters, were indeed positive for T. gondii (54 % and 33 %, respectively). Mussels from Point Lobos, CA, were also contaminated (31 %) with Cryptosporidium oocysts. Phylogenetic analysis using the 18S rRNA gene revealed that two distinct Cryptosporidium parvum-like subtypes were detected. Overall, this study introduced a novel method to isolate parasite DNA from mussel tissue, and demonstrated the feasibility of using indigenous Mytilus spp. as biosentinels for monitoring microbial water quality. More importantly, using this method, a high prevalence of Cryptosporidium spp. and T. gondii oocyst DNA was detected in mussels collected from the California coastline.
Record Details:Record Type: DOCUMENT
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL EXPOSURE RESEARCH LABORATORY
MICROBIOLOGICAL AND CHEMICAL EXPOSURE ASSESSMENT DIVISION
BIOHAZARD ASSESSMENT RESEARCH BRANCH