Abstract
Shellfish are known as a potential source of Toxoplasma gondii (responsible for toxoplasmosis), and Cryptosporidium parvum, which is one of the major causes of gastroenteritis in the world. Here we performed a comprehensive qPCR-based monthly survey for T. gondii and C. parvum during 2016 and 2017 in oysters (Crassostrea virginica) (n = 1440) from all six sites along the coast of Maine (USA). Pooled samples (mantle, gills, and rectum) from individual oysters were used for DNA extraction and qPCR. Our study resulted in detections of qPCR positives oysters for T. gondii and C. parvum at each of the six sites sampled (in 31% and 10% of total oysters, respectively). The prevalence of T. gondii was low in 2016, and in September 2017 several sites peaked in prevalence with 100% of the samples testing positive. The prevalence of C. parvum was very low except in one estuarine location (Jack’s Point) in June 2016 (58%), and in October of 2016, when both prevalence and density of C. parvum at most of the sampling sites were among the highest values detected. Statistical analysis of environmental data did not identify clear drivers of retention, but there were some notable statistically significant patterns including current direction and nitrate along with the T. gondii prevalence. The major C. parvum retention event (in October 2016) corresponded with the month of highest dissolved oxygen measurements as well as a shift in the current direction revealed by nearby instrumentation. This study may guide future research to locate any contributing parasite reservoirs and evaluate the potential risk to human consumption.
Highlights
Toxoplasma gondii and Cryptosporidium parvum are two cosmopolitan protozoan parasites relevant to public health [1]
Beach in New York were positive for C. parvum using a PCR-based assay (1% and 50% prevalence for the two positive sites), the DNA was identified mostly in the gills and the foot, and the prevalence of C. parvum assemblage varied in the examined species even when they were collected within a short distance from one another [25]
Our study represents a broad snapshot for these protozoan parasites in oysters from Maine; both origin and abilities of the oocysts to sporulate in oyster tissues were outside the scope of this study, and they remain unknown
Summary
Toxoplasma gondii and Cryptosporidium parvum are two cosmopolitan protozoan parasites relevant to public health [1]. The definitive hosts for T. gondii are felines, including both feral and pet domestic cats, and others such as bobcats and pumas. Carnivores acquire T. gondii from consuming infected prey; though other animals (including humans) can incidentally acquire the parasite through foodborne pathways, and in the case of humans, consuming undercooked meat, contaminated plants and water, contact with cat litter, and blood transfusions, are additional sources of infection [2]. Estimates show that T. gondii infects 2 billion people worldwide with most infected individuals remaining asymptomatic. Despite the lack of symptoms in those with good health, T. gondii is a significant threat to AIDS patients and otherwise immunosuppressed patients, as well as pregnant women [3]. T. gondii has attracted public attention due to numerous publications linking toxoplasmosis to mental disorders [4,5,6,7] and problematic behaviors (e.g., increased likelihood of risky road behaviors that have been associated with traffic accidents and ‘risk taking’ related to business decisions) [8,9]
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