‘Sushi Parasites’ Up 283-Fold in Last Four Decades

(CN) — A worm may be hitching a ride on your next plate of sushi – and it’s not some trendy new food craze.

Researchers at the University of Washington delivered the icky news Thursday that “sushi parasites” have been on the rise for the last 37 years and no one noticed.

An anisakis worm is seen in a filet of salmon. These parasitic worms can be up to 2 centimeters in length and are found in the flesh of raw and undercooked fish. (Togabi / Wikimedia Commons)

Take a deep breath. Nobody wants to eat a worm in their next plate of fresh sashimi but according to the study published in the journal Global Change Biology the anisakis or “herring worm” cannot reproduce in the human intestine.

At most, the study authors say, humans chalk up any infestation to a case of food poisoning.

Disease spread from animals, or zoonosis, is on everyone’s mind thanks to the leading theory behind the spread of the novel coronavirus COVID-19, which is believed to have originated from a “wet market” or live animal market in Wuhan, China.

But zoonotic disease accounts for 58% of infectious diseases across the globe, including rabies and malaria, according to the study authors who tracked the rise of the marine worm anisakis.

From 1978 to 2015, the anisakis worm saw a 283-fold increase in abundance throughout marine wildlife.

Found in undercooked or raw fish and measuring about the size of a U.S. nickel, the anisakis causes a disease that is magnitudes different than COVID-19.

Assistant professor Chelsea Wood at the UW School of Aquatic and Fishery Sciences and a corresponding author of the study says neither the anisakis nor the disease it causes – anisakiasis or anisakidosis – can be transmitted from human to human.

The symptoms of the disease are similar to those of other types of food poisoning: Burning or painful tingling in arms or legs, headache, nausea, vomiting, diarrhea, hallucinations, and temperature reversal: cold objects feel hot and hot objects feel cold.

In the developing world most people don’t not think of wildlife when they think of disease, Wood told Courthouse News.

“Disease links us to nature,” said Wood. The question on why there has been such an uptick in infectious diseases across the globe has been a persistent question for researchers in her field.

The transmission to humans from the food chain starts when shrimp or small crustaceans eat a freshly hatched anisakis worm. The truism follows that there is always a bigger fish to eat the smaller fish. Eventually the parasite makes its way to a seafood market or before a sushi chef.

Wood said processors and sushi chefs are adept at removing any parasites. The study looked at fish freshly caught from the ocean.

The study illustrates the health risk to both human and marine mammals over the last four decades, said Wood. Humans will be inconvenienced by their bout of “food poisoning,” but the effects to marine mammals remains unknown.

Researchers compared the rise of the anisakis parasite to another parasitic nematode, the pseudoterranova or “cod worm.” While the anisakis saw a dramatic jump in its population over a 37-year time period, the pseudoterranova saw no change.

“On average, we estimated that Anisakis spp. abundance increased from less than 1 anisakid per one hundred hosts in 1978 to more than 1 anisakid in every host examined in 2015,” the study authors wrote. “This pattern was not driven by any single host species.”

The black scabbardfish was most represented among infected marine life but did not drive the pattern observed across all hosts and no one specific region saw a larger pattern.

There is no clear explanation for the increase, but rising temperatures in ocean waters, agricultural runoff and additional safeguards under the Marine Mammal Protection of 1972 are the leading theories.

Seals, sea lions, whales and dolphin populations benefitted from the protection, which likely meant more hosts roaming the ocean according to Wood.

An increase in parasitic worms could signal the ecosystem is doing well, but more vulnerable marine mammal populations are at risk. When discussing conservation efforts for marine life, Wood said few consider the spread of parasitic worms which may provide a powerful explanation for the failure of some populations to recover.

Research was also conducted by Bates College in Maine, Washington Sea Grant and UW graduate student Evan Fiorenza.

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