ANSES portraits –“I study parasites in seafood products” – Mélanie Gay

Mélanie Gay

Mélanie Gay is Deputy Head of the Bacteriology and Parasitology of Fishery and Aquaculture Products unit of ANSES's Laboratory for Food Safety on the Boulogne-sur-Mer site. She studies parasites that infect fish and that are likely to cause food poisoning in humans.

“I have developed activities relating to the parasitology of fishery products at ANSES”

When I arrived in 2005, no work on the parasitology of fishery products was being undertaken at ANSES. I started developing research and reference activities dealing with this theme. With regard to the reference work carried out, I am deputy to the manager of the National Reference Laboratory on foodborne parasites. We are involved in the development and validation of methods for detecting and identifying parasites, and we carry out analyses as part of surveillance plans and to respond to requests from the public authorities. 

I initially worked on Anisakidae, which are the zoonotic (can spread from animals to humans) parasites most commonly found in fishery products in France. The Anisakidae are a family of nematodes, i.e. non-segmented roundworms. They parasitise marine fish and if ingested by humans can cause digestive disorders and/or allergies.

“I participate in research projects to better understand why there are more parasites in some situations than in others”

I participate in research projects to better understand why some fish are more infected with parasites than others. Indeed, the infestation level can vary considerably depending on the season, the geographical area, the species, etc. We study fish caught as part of scientific campaigns carried out in collaboration with Ifremer, and we also investigate fish at the sale and processing stages. This work is useful for both the fishing industry and the authorities, to identify best practices and determine what sampling plans are necessary to verify the absence of parasites.

“Our results showed that frozen parasites died after three days”

One of my research projects was devoted to the effect of domestic freezing on parasites. This step is important to eliminate parasites from fishery products that are eaten in raw or undercooked preparations such as sushi or ceviche. Our results showed that parasites were still alive after seven days in one- and two-star freezers, whose minimum temperature was greater than or equal to -12°C, but that they died after three days in three- and four-star freezers, capable of reaching a temperature of -18°C. 

“We described the presence of a little-known parasite in the English Channel and the North Sea”

More recently, in addition to carrying out work on Anisakidae, we focused on trematodes (or flukes), another group of parasites. These are non-segmented flatworms. For the first time, we identified the presence of one of them, called Cryptocotyle, in the English Channel and the North Sea as part of the thesis work of Maureen Duflot, which I supervised and which was defended in 2021. For the time being, we do not know whether this parasite is zoonotic. However, given that it is similar to other species that are indeed zoonotic, it will be worthwhile to conduct more in-depth studies on this subject and inform fishing professionals of our findings. Maureen Duflot is continuing her work as part of a postdoctoral contract financed by the Hauts-de-France Region in collaboration with the Laboratory for Animal Health to assess the zoonotic potential of Cryptocotyle.

Lastly, we are studying Clinostomum complanatum, a freshwater trematode that was not found in France until late 2019. There are very few data on this parasite. We know that it is zoonotic, but the only known cases of food poisoning caused by this parasite occurred in Asia. Some specialists think this is because the Clinostomum found in Europe and Asia belong to two separate species, while others consider that the absence of cases in Europe is due to differences in culinary practices: traditionally, consumers of freshwater fish in Europe have been more likely to eat them cooked.  

Therefore, we are carrying out applied research in conjunction with professionals and the health authorities and also more fundamental research, which involves for example studying the distribution of parasites in marine ecosystems and describing little-known species. I particularly enjoy alternating between these two approaches. Furthermore, the diversity of the parasites contained in fishery products and the lack of data on their distribution, taxonomy and zoonotic potential are opening up many new opportunities for work such as that undertaken on trematodes!