Gone Fishing: Parasite Edition

In 1984, a 34-year-old Hawaiian resident of Japanese origin experienced intermittent abdominal pain coupled with inexplicable hunger pangs. Her diagnosis was the first of its kind to be reported in the United States: a confirmed case of parasitic penetration of the stomach lining. The identified cause of the infection was a third stage Anisakis simplex larva. From the patient’s food consumption history, it was evident that raw seafood such as tuna, salmon, and poki were a predominant part of her diet. This case and others got public health and environmental experts alike thinking more about zoonotic diseases.

Zoonosis occurs when the infection causing agent is transmitted between two different species, usually from animals to humans. Like anisakiasis, most zoonotic diseases are often mistaken for food poisoning because of the strong similarities between symptoms. The four primary manifestations of zoonoses may be gastric, intestinal, ectopic, and even as allergies. It is remarkable how the son of a watchmaker, Felix Dujardin, initially paved the path for a better understanding of zoonotic diseases. He first described the infection in 1845 by naming the worm he found in dolphins as Anisakis.

Surge in the Marine Parasite Population

A recent study conducted by the University of Washington revealed an alarming increase in the population size of marine parasites. The study demonstrated that, over the span of 40 years, the population size experienced a 283-fold increase in parasites. There exists a common observation between the 1986 findings of the research team that were observing anisakid nematodes within Hawaii and the 2020 study conducted by the research group from the University of Washington; salmon was more likely to be infected by marine parasites. This finding does not rule out the susceptibility of other seafood species to parasitic infections.

Possible Rationale Behind the Increase in Marine Parasite Population

Researchers are unable to pinpoint a specific reason behind the parasites’ population explosion. Various speculations (that are worth pursuing) co-exist, such as climate change, the introduction of fertilizers from field runoffs, global policies that preserve marine mammals (thereby increasing their population), and an increase in testing frequency. Over the past decade, the focus has intensified on our global water footprint, which has resulted in more extensive and frequent marine testing methodologies.

Understanding Seafood Parasite Behavior Is Important

It is important to convert awareness into action. The data obtained from studying seafood parasites helps us to conduct a pulse check on the overall “health” of the marine ecosystem, specifically of the mammals. If marine parasites prefer one species over another, then parasite population size could also be used as an indicator of the growth or suppression of other marine species.

A Food Safety and Quality Perspective

Sushi, sashimi, and ceviche have and will continue to remain popular delicacies around the world. With effective food safety measures in place such as obtaining seafood from trusted (and approved) suppliers, maintaining temperature control from dispatch until service, monitoring the pH (where applicable), and ensuring only fresh stocks are utilized, consumer safety can be assured. In most positive cases of zoonoses linked to salmon, the fish was obtained and served chilled, versus frozen.

For sushi lovers out there, it is a great idea to slice the piece of fish at least in half and do a visual check if you can, before consuming it. Even though some chefs may be meticulous with their visual checks, it is not uncommon for an unsuspecting parasite or two to slip away from the well-trained eye.