'Sushi parasites' have increased 283-fold in past 40 years - Science Daily

'Sushi parasites' have increased 283-fold in past 40 years - Science Daily
Study on parasitic worms presents a cautionary tale for sushi lovers - Inverse
500-million-year-old fossilized poop reveals a nightmarish, predatory sea worm - SYFY WIRE

Posted: 19 Mar 2020 08:39 AM PDT

The next time you eat sashimi, nigiri or other forms of raw fish, consider doing a quick check for worms.

A new study led by the University of Washington finds dramatic increases in the abundance of a worm that can be transmitted to humans who eat raw or undercooked seafood. Its 283-fold increase in abundance since the 1970s could have implications for the health of humans and marine mammals, which both can inadvertently eat the worm.

Thousands of papers have looked at the abundance of this parasitic worm, known as Anisakis or "herring worm," in particular places and at particular times. But this is the first study to combine the results of those papers to investigate how the global abundance of these worms has changed through time. The findings were published March 19 in the journal Global Change Biology.

"This study harnesses the power of many studies together to show a global picture of change over a nearly four-decade period," said corresponding author Chelsea Wood, an assistant professor in the UW School of Aquatic and Fishery Sciences. "It's interesting because it shows how risks to both humans and marine mammals are changing over time. That's important to know from a public health standpoint, and for understanding what's going on with marine mammal populations that aren't thriving."

Despite their name, herring worms can be found in a variety of marine fish and squid species. When people eat live herring worms, 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 worm dies after a few days and the symptoms disappear. This disease, called anisakiasis or anisakidosis, is rarely diagnosed because most people assume they merely suffered a bad case of food poisoning, Wood explained.

After the worms hatch in the ocean, they first infect small crustaceans, such as bottom-dwelling shrimp or copepods. When small fish eat the infected crustaceans, the worms then transfer to their bodies, and this continues as larger fish eat smaller infected fish.

Humans and marine mammals become infected when they eat a fish that contains worms. The worms can't reproduce or live for more than a few days in a human's intestine, but they can persist and reproduce in marine mammals.

Seafood processors and sushi chefs are well-practiced at spotting the worms in fish and picking them out before they reach customers in grocery stores, seafood markets or sushi bars, Wood explained. The worms can be up to 2 centimeters in length, or about the size of a U.S. 5-cent nickel.

"At every stage of seafood processing and sushi preparation, people are good at finding worms and removing them from fish," Wood said.

Some worms can make it past these screening steps. Still, Wood -- who studies a range of marine parasites -- said she enjoys eating sushi regularly. For sushi consumers who remain concerned about these worms, she recommends cutting each piece in half and looking for worms before eating it.

For the analysis, the study's authors searched the published literature archived online for all mentions of Anisakis worms, as well as another parasitic worm called Pseudoterranova, or "cod worm." They whittled down the studies based on set criteria, ultimately keeping only those studies that presented estimates of the abundance of each worm in fish at a given point in time. While Anisakis worms increased 283-fold over the study period of 1978 to 2015, Pseudoterranova worms did not change in abundance.

Although the health risks of these marine worms are fairly low for humans, scientists think they may be having a big impact on marine mammals such as dolphins, whales and seals. The worms actually reproduce in the intestines of these animals and are released into the ocean via the marine mammals' feces. While scientists don't yet know the physiological impacts of these parasites on marine mammals, the parasites can live in the mammals' bodies for years, which could have detrimental effects, Wood said.

"One of the important implications of this study is that now we know there is this massive, rising health risk to marine mammals," Wood said. "It's not often considered that parasites might be the reason that some marine mammal populations are failing to bounce back. I hope this study encourages people to look at intestinal parasites as a potential cap on the population growth of endangered and threatened marine mammals."

The authors aren't sure what caused the large increase of Anisakis worms over the past several decades, but climate change, more nutrients from fertilizers and runoff, and an increase in marine mammal populations over the same period could all be potential reasons, they said.

Marine mammals have been protected under the Marine Mammal Protection Act since 1972, which has allowed many populations of seals, sea lions, whales and dolphins to grow. Because the worms reproduce inside marine mammals -- and their rise occurred over the same time period as the mammals' increase -- this is the most plausible hypothesis, Wood said.

"It's possible that the recovery of some marine mammal populations has allowed recovery of their Anisakis parasites." Wood said. "So, the increase in parasitic worms actually could be a good thing, a sign that the ecosystem is doing well. But, ironically, if one marine mammal population increases in response to protection and its Anisakis parasites profit from that increase, it could put other, more vulnearble marine mammal populations at risk of increased infection, and that could make it even more difficult for these endangered populations to recover."

Study on parasitic worms presents a cautionary tale for sushi lovers - Inverse

Posted: 19 Mar 2020 04:14 PM PDT

The next time you dig into a sushi dinner, the bougiest of takeout meals, it might be worth stopping to both inspect and savor. According to the results of recent research, the odds of you finding something unexpected inside have gone up astronomically in recent years.

Just like humans who occasionally end up with 5 foot-long tapeworms protruding from their rectums, marine mammals also struggle with parasitic visitors. Dolphins and whales play host to a genus of worms called Anisakis – parasitic nematodes that take shelter in their poop and go on to infect shrimp, fish, and then, more marine mammals in a vicious cycle (or humans who eat them while they're in any of those intermediate hosts). Meanwhile, seals and sea lions tend to be the final destination for a genus called Pseudoterranova, also known as the "cod worm" — a roundworm that can also affect humans who eat undercooked seafood.

According to a new study, between 1967 and 2013, the abundance of anisakids increased 283-fold over that period of time. It turns out there are far more worms in the sea than we thought.

This analysis was published Thursday in the journal Global Change Biology.

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

What does this mean for human health?

The study's senior author Chelsea Wood, an assistant professor at the University of Washington, says that, fortunately, there's not a need for sushi-lovers to be too worried.

Sill, when anisakid nematodes (also known as the herring worm) find their way into the human body, they can cause a condition called anisakiasis, which is when the worms attach to the inside of the esophagus, stomach, or intestine.

"They can cause some damage on the way out."

It sounds gross, but Wood tells Inverse that these worms can't survive in human digestive tracts for very long. They can drive an immune response in the intestinal lining — and that can cause nausea, vomiting, diarrhea and abdominal pain. But especially during the coronavirus pandemic, we have far bigger concerns as far as infections go, she says.

"Being infected with anisakis is not a pleasant experience. Folks who consume live anisakid worms won't suffer long term effects," she says. "But they can cause some damage on the way out."

The more intriguing mystery is why are these worms thriving? The answer may affect the way we feel about our seafood dinners, but also more pressingly, tells us a lot about how life is changing in our oceans for better and worse.

Why so many worms?

Wood's study is a meta-analysis of 123 papers on herring and cod worms that have been published in the past 40 years. Taken together, that work illuminated two stark patterns. The rates of herring worms are skyrocketing, whereas the rates of cod worms haven't increased significantly.

Wood says that it's basically impossible to tease apart why one worm seems to be thriving while the other isn't. But as far as the rise of the herring worms, the ones that more often go on to affect people, she has three preliminary explanations.

"It's hard to wrap your head around – that a 283-fold increase in this gross parasite is a sign that the ecosystem is doing well."

One is actually tinged with good news. The period this study was conducted in actually overlaps "directly" with marine mammal protection legislation like the Marine Mammal Protection Act, says Wood. Sparing host mammals from exploitation and unnecessary slaughter gives parasites more places to thrive.

Anisakis worms in blue whiting fish. The prevalence of these worms, found in raw or undercooked fish, has increased dramatically since the 1970s.Gonzalo Jara/Shutterstock

"It's hard to wrap your head around – that a 283-fold increase in this gross parasites is a sign that the ecosystem is doing well," she says. "But parasites are dependent on hosts, and if their hosts are doing well, then their parasites are going to do well."

But there are two competing explanations, that position the situation more negatively: As ocean temperatures rise due to the climate crisis, some parasites are going extinct. The worms examined here may just be reproducing faster, leading to bigger parasitic families that may still die off sooner rather than later.

It's also possible that human nutrient pollution could also be spurring them on. As agricultural, logging or development runoff finds its way into the ocean, it brings with it nutrients, says Wood. This may be setting off a vicious cycle: Those nutrients fuel the growth of phytoplankton (tiny plants), which feed tiny crustaceans, who serve as additional hosts for tiny parasitic worms.

What this means for dinner

Regardless of how and why Anisakis worms have thrived in the past decades, humans will likely do just fine. As Wood notes in a statement, most sushi chefs are trained to catch such worms in raw fish. And if you're worried a bit of closer inspection can't hurt.

Even if you do contract a worm, the result isn't threatening to your health, adds Wood — despite how uncomfortable you might become. The human body can get rid of worms eventually: The CDC notes many people "can often extract the worm manually from their mouth or cough up the worm and prevent infection."

Vomiting, while not very fun, may also expel the worm from your insides.

Unfortunately, marine mammals aren't so lucky. These worms can stick around in their bodies and reproduce, says Wood. We know that when worms linger in human stomachs, they can cause issues like cognitive impairment. But we don't know how this might play out in marine mammals, says Wood, though there could be risks to their health that we don't know about yet.

"There's a potential for a huge health burden on whales and dolphins that are infected," Wood explains.

In summary: Humans may breathe a sigh of relief regarding the safety of eating a sushi dinner. But for those marine mammals who live raw fish each and every day, we're not sure of what their increasingly-wormy future might hold.

Abstract: The Anthropocene has brought substantial change to ocean ecosystems, but whether this age will bring more or less marine disease is unknown. In recent years, the accelerating tempo of epizootic and zoonotic disease events has made it seem as if disease is on the rise. Is this apparent increase in disease due to increased observation and sampling effort, or to an actual rise in the abundance of parasites and pathogens? We examined the literature to track long-term change in the abundance of two parasitic nematode genera with zoonotic potential Anisakis spp. and Pseudoterranova spp. These anisakid nematodes cause the disease anisakidosis and are transmitted to humans in undercooked and raw marine seafood. A total of 123 papers published between 1967 and 2017 met our criteria for inclusion, from which we extracted 755 host–parasite–location–year combinations. Of these, 69.7% concerned Anisakis spp. and 30.3% focused on Pseudoterranova spp. Meta-regression revealed an increase in Anisakis spp. abundance (average number of worms / fish) over a 53-year period from 1962 to 2015 and no significant change in Pseudoterranova spp. abundance over a 37-year period from 1978 to 2015. Standardizing changes to the period of 1978 to 2015, so that results are comparable between genera, we detected a significant 283-fold increase in Anisakis spp. abundance and no change in abundance of Pseudoterranova spp. This increase in Anisakis spp. abundance may have implications for human health, marine mammal health, and fisheries profitability.

500-million-year-old fossilized poop reveals a nightmarish, predatory sea worm - SYFY WIRE

Posted: 19 Mar 2020 07:48 AM PDT

No, this isn't a B-horror movie from the '80s, but if it was, it would probably be a cult classic by now.

What a primordial sea worm ate hundreds of millions of years ago emerged in its fossilized poop. The mutilated pieces of trilobites and other animals in that poop tell of a creature that lurked on the ocean floor, lurking in its burrow and waiting for prey to swim by unaware. That was what University of Kansas researcher Julien Kimmig and his team found out when they unearthed these burrows and fossilized feces, or coprolites. Turns out that something normally flushed down the toilet—and this worm's burrows were its toilet—can be a time capsule of what ate what.

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"These are burrows of a wormlke animal where we have fossilized feces preserved," said Kimmig, who published a study in Palaios. "This is rare because feces decompose very easily — it's not a stable product from animals."

So how did these (insert poop emoji here) manage to fossilize into coprolites? When something goes, it has to go in the right conditions.

Coprolites are much more likely to form in a body of water when the sink to the bottom. With this worm, which was one of the most monstrous predators in its ecosystem at 6-12 inches long and about three-quarters of an inch wide, there was already an advantage since it pooped directly into a burrow that was up to a foot deep. This environment has barely any oxygen and is crawling with anaerobic bacteria, which don't need oxygen to survive. These bacteria replace organic matter with phosphates and minerals over millions of years.

What an organism eats doesn't really matter if it poops in the right place to turn what it leaves behind into a coprolite, but interestingly enough, carnivores like this worm stand a better chance of preserving the remnants of what they ate. Exoskeletons and shells of prey such as trilobites, clam-like bivalved arthopods, and hyoliths, which looked sort of like snails with strange pointed shells, are already mineralized.

Where the things devoured by this worm do matter is in figuring out the Cambrian food web.

"A food web is basically the interaction between what is eating what in the ecosystem," Kimmig said. "When you think of fossils, fossilized poop isn't what you're thinking of — but actually it's one of the most important indicators of paleoenvironmental interactions because it gives us information on what was a predator in the area and what it ate."

The pieces of preserved shells and exoskeletons that surfaced in the coprolites gave away that this worm was a predator, thought to be much like the existing and equally terrifying Bobbitt worm. If you had any creeping suspicions, Bobbitt worms are named after what you probably think they are, and they shoot out of their burrows and use the frightening predatory appendages in their mouths to grab prey seemingly out of nowhere. Not even an octopus or stonefish is safe if it happens to be floating around near a hidden Bobbitt worm. The modus operandi of the ancient version appears to have been similar. Neither of them have or had a brain.

By the way, detrivores, basically garbage-feeders, would take advantage after the predatory worm did its business and left its burrow. They feasted on undigested leftovers in the poop.

After this, you'll probably never think of a toilet the same way again.

(via University of Kansas)

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'Sushi parasites' have increased 283-fold in past 40 years - Science Daily