Since the 1970s, the concentration of parasites that can be found in raw fish has increased 283 times , a new study led by the University of Washington suggests. This growth could have implications for human health and for marine mammals. The findings have been published in the journal Global Change Biology , on March 19, 2020.
Specifically, a parasite known as Anisakis has been analyzed, which is only contracted if you eat fish or parasitized cephalopods raw or subjected to preparations that do not eliminate the parasite.
According to Chelsea Wood , assistant professor in the School of Aquatic and Fisheries Sciences at the University of Washington, and leader of the research, this study is pioneering when it comes to analyzing other studies and projecting the evolution of this parasite over time , in this case four decades.
To perform the analysis, all mentions of Anisakis, as well as another parasite called Pseudoterranova , were searched in the scientific literature archived online . They then narrowed the search field to studies based on established criteria, and only kept those that presented estimates of the abundance of each parasite in fish at any given time.
While the Anisakis increased 283 times during the study period from 1978 to 2015 , the Pseudoterranova did not show any increase.
Contagion
The authors are not sure of the origin of this large increase in Anisakis in recent decades, but climate change, among other factors, could be behind the phenomenon.
The contagion process works like this, in a basic way : first the nematode is born in the ocean, then it infects small crustaceans that live at the bottom of the ocean, when the fish eat the infected crustaceans they also become infected, and this chain of contagion continues through larger fish eating infected fish.
When fish reach humans and this nematode is ingested, the parasite can invade the intestinal wall and cause symptoms that mimic those of food poisoning, such as nausea, vomiting, and diarrhea. In most cases, the nematode dies after a few days and the symptoms disappear. This disease, called anisakiasis or anisakidosis , is rarely diagnosed because most people assume that they were simply victims of a severe case of food poisoning.
But it should be noted that these nematodes, which can be up to two centimeters in length, cannot reproduce or live for more than a few days in the human intestine, they can remain and reproduce in marine mammals for longer.
Thus, although the health risks are quite moderate for humans, scientists believe that they may be having a major impact on marine mammals such as dolphins, whales and seals : although the physiological impact of These parasites in marine mammals can live in their bodies for years, which must probably have detrimental effects.
As Wood explains: “One of the important implications of this study is that we now know that there is a massive and growing health risk to marine mammals. It is not often considered that parasites could be the reason why some populations of mammals marine mammals are not recovering, I hope this study encourages people to view intestinal parasites as a potential limit to the growth of the endangered marine mammal population.
Reference: Evan A. Fiorenza et al, It’s a wormy world: Meta-analysis reveals several decades of change in the global abundance of the parasitic nematodes Anisakis spp. and Pseudoterranova spp. in marine fishes and invertebrates, Global Change Biology (2020). DOI: 10.1111 / gcb.15048.
