Abstract
The issue of whether market fish can be involved in the transmission of Toxoplasma gondii in the marine environment is highly debated since toxoplasmosis has been diagnosed frequently in cetaceans stranded along the Mediterranean coastlines in recent times. To support the hypothesis that fishes can harbour and effectively transmit the parasite to top‐of‐the‐food‐chain marine organisms and to human consumers of fishery products, a total of 1,293 fishes from 17 species obtained from wholesale and local fish markets were examined for T. gondii DNA. Real‐time PCR was performed in samples obtained by separately pooling intestines, gills and skin/muscles collected from each fish species. Thirty‐two out of 147 pooled samples from 12 different fish species were found contaminated with T. gondii DNA that was detected in 16 samples of skin/muscle and in 11 samples of both intestine and gills. Quantitative analysis of amplified DNA performed by both real‐time PCR and digital PCR (dPCR) confirmed that positive fish samples were contaminated with Toxoplasma genomic DNA to an extent of 6.10 × 10−2 to 2.77 × 104 copies/ml (quantitative PCR) and of 1 to 5.7 × 104 copies/ml (dPCR). Fishes are not considered competent biological hosts for T. gondii; nonetheless, they can be contaminated with T. gondii oocysts flowing via freshwater run‐offs (untreated sewage discharges, soil flooding) into the marine environment, thus acting as mechanical carriers. Although the detection of viable and infective T. gondii oocysts was not the objective of this investigation, the results here reported suggest that fish species sold for human consumption can be accidentally involved in the transmission route of the parasite in the marine environment and that the risk of foodborne transmission of toxoplasmosis to fish consumers should be further investigated.
Highlights
The apicomplexan Toxoplasma gondii is a global zoonotic parasite affecting humans and animals, both terrestrial and aquatic, that causes a cosmopolitan food and waterborne infection, with an es‐ timated 1–2 billion of the world's population infected (Bahia‐Oliveira, Gomez‐Marin, & Shapiro, 2017)
The issue of whether market fish can be involved in the transmission of Toxoplasma gon‐ dii in the marine environment is highly debated since toxoplasmosis has been diagnosed frequently in cetaceans stranded along the Mediterranean coastlines in recent times
Toxoplasma gondii DNA was detected in mainly piscivorous species (A. laterna, M. merluccius, R. clavata, S. scrofa and T. trachurus), in om‐ nivorous fishes (B. boops, P. acarne and P. erythrinus) and in species feeding on small benthic invertebrates or zooplankton
Summary
The apicomplexan Toxoplasma gondii is a global zoonotic parasite affecting humans and animals, both terrestrial and aquatic, that causes a cosmopolitan food and waterborne infection, with an es‐ timated 1–2 billion (approximately 30%) of the world's population infected (Bahia‐Oliveira, Gomez‐Marin, & Shapiro, 2017). The risk factors for human and animal infection include consuming infected raw or undercooked meat; ingestion of contaminated water, soil, vegeta‐ bles or anything contaminated with oocysts shed in faeces; blood transfusion or organ transplants; intrauterine or transplacental transmission; and drinking infected unpasteurized milk (Aguirre et al, 2019). Despite the consump‐ tion of raw or undercooked meat harbouring T. gondii cysts is still considered the most likely source of infection, in the last 40 years' toxoplasmosis outbreaks associated with exposure to oocysts‐con‐ taminated water have been reported in Panama (Benenson, Takafuji, Lemon, Greenup, & Sulzer, 1982), in British Columbia (Bowie et al, 1997), in Brazil (De Moura et al, 2006) and in India (Balasundaram, Andavar, Palaniswamy, & Venkatapathy, 2010) with the latter two episodes resulting from the ingestion of municipal drinking water. The majority (78%) of congenital toxoplasmosis cases from four epidemics in North America originated from oocysts ex‐ posure, though only 49% of these cases could be confirmed as food‐ borne (Aguirre et al, 2019)
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