Horseshoe crabs have a vital role in the development of a coronavirus vaccine. Here's why.

GREENVILLE, S.C. — Allen Burgenson had a job, his father explained as they stood on the sand.This was Allen's

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GREENVILLE, S.C. — Allen Burgenson had a job, his father explained as they stood on the sand.

This was Allen's first fishing trip, but he wasn't going to take anything from the bay. He was to return the water's gifts to the deep, where they'd belonged for hundreds of millions of years. 

If he spotted a horseshoe crab on its back, his father said as he held Allen's hand, that meant it was in trouble and needed Allen's help to get home. Allen just had to flip it over. Its 10 legs could then make it the rest of the way back to the crashing waves. 

Allen did just that on that day in 1963 in Sandy Hook, New Jersey, when he was just 3 years old. That's what he still does today. Whenever Burgenson enjoys a stroll along the East Coast, he is still a lookout for the stranded sea creature that's unlike anything else on the planet.

But in 1963, Burgenson didn't know that inside each of those ancient animals he saved was something that would help save millions of us during his lifetime.

Now, in 2020, the horseshoe crab is poised to assume a vital role in a drug the whole world awaits, a COVID-19 vaccine.

Around the same time Burgenson was a boy on a beach, Jack Levin and Frederik Bang began to collaborate on horseshoe crab blood experiments. Their work led to a process that channels the almost magical force of the horseshoe crab's immune system, one that's helped the animal survive longer than most of the species that ever roamed the Earth or scurried across the ocean floor. 

'The world's health care can thank the horseshoe crab'

Since the late 1970s, horseshoe crab blood has been approved to make what's called the Limulus amebocyte lysate test, or the LAL test — an alarm system triggered by a type of bacteria that can cause fever, and in some cases, death.

Simply put, it works like this: A mixture of lysate is first made from the horseshoe crab's amebocyte or blood cells. Next, that fluid is added to whatever material a researcher is testing for safety. Depending on the test, the fluid will either clot or change color to signal the presence of a dangerous toxin.

John Dubczak, an executive director with Charles River Laboratories, one of the company's licensed by the U.S. Food and Drug Administration to produce the LAL test, put the test's impact in bold terms: "[It] has unequivocally elevated the quality and safety of injectable pharmaceutical drugs and medical devices and that includes all of vaccines that protect us," he wrote.

This creature, usually no bigger than about 19 inches across, has a significance that outsizes its foot — or claw — print. The Limulus polyphemus, or Atlantic horseshoe crab, lives only up and down the coast of Eastern North America and a small part of Central America. Not even a half a million horseshoe crabs were brought to biomedical facilities in 2018, according to the most recently published data from the Atlantic States Marine Fisheries Commission.

"The world's health care can thank the horseshoe crab," Burgenson said. 

On Sept. 16, Robert Redfield, director of the Centers for Disease Control and Prevention, told a Senate panel that a vaccine might not be ready until next year. On the same day he testified, the novel coronavirus cases totaled about 30 million globally, with about 942,000 associated deaths. 

No matter what vaccine in trial now wins the race to market, LAL will be standard to test the safety of any materials that go into the medication, as well as the final product itself. All of that LAL will come from just four production facilities in South Carolina, Massachusetts, Maryland and Virginia.

The demand of five billion COVID-19 vaccine doses won't be a burden, said Burgenson, who is now the chair of Horseshoe Crabs Advisory Panel to the Atlantic States Marine Fisheries Commission. He estimates that at most, the facilities about three days of normal production to provide the material needed to test the vaccine's safety, with just one of those days of production to test the vaccine itself.

And this gift will be given by an animal that's been long misunderstood and maligned, said Burgenson, a microbiologist with almost 40 years of experience in the pharmaceutical industry.

The horseshoe crab has long been overlooked and overfished. Humans are the biggest threat to the invertebrate with ancestry that traces to the age before the dinosaurs, a time more than 400 million years before humans walked the earth. 

And when we did finally meet them, we didn't even get the thing's name right. Turns out, the horseshoe crab is not even a crab. 

A dead Horseshoe Crab lies dead on Ben T. Davis beach Thursday afternoon July 31.2008 in Tampa, Fla. City officials closed the beach after hundreds of dead fish washed up on shore.

What is a horseshoe crab, really?

Horseshoe crabs are more closely related to the spider than the crab, said Daniel Sasson, assistant marine scientist at South Carolina's Department of Natural Resources. Its physical traits make that point. Like the spider, it has a lot of legs and eyes and pincher claws they use to feed. 

That's not to say they don't have anything in common with the crab. Like a crustacean, it will shed an exoskeleton as it grows. You might have seen one washed ashore, especially after a storm.

It's also got something that looks like a tail but is actually called a telson — used to flip over the body, which can weigh 10 pounds. It's not poisonous. It's not a weapon, even though it looks scary enough to show up in a sci-fi scene.

All these attributes add up to one rugged, hardened tank-looking thing. Asteroids and volcanoes haven't even been able to take them out.

The blue blood is its best line of defense. Cells essentially build a fortress in seconds.

Amoebocytes, a type of blood cell, can "detect any outside particle," Sasson said, and once they do, they spring into action, whether the enemy invader is in the bloodstream or a wound outside of the body.   

"How quickly the blood coagulated around the wound was amazing," he said. "Say you break off a piece of a claw. You'd see a little bit of blood for, you know, 10,15 seconds. And then it would stop because it would already have coagulated completely where the wound was."

Horseshoe crab spawning season spawns much more

For a spell each year, the horseshoe crab crawls to the beaches to reproduce, and this ritual provides a rich and unusual opportunity for up-close study on beaches from Mexico to Florida, Georgia to Maine.

The peak is also typically during evening high tides under a full or new moon. Females will lay about 4,000 greenish eggs, each one about the size of the head of a pin. She might lay several clusters over the course of the season, up to 100,000 in all. 

Some males arrive on land attached to the female's back. Others join them to compete to mate. They will huddle together, often in clusters of maybe five or six — unless you are in Delaware Bay, the epicenter of spawning for this species. There, the clusters are big enough to call galaxies.

Sasson saw the spectacle once. He heard it first. 

"You could hear the clacking of their shells from, you know, way before you got to the beach," he said. Hundreds of thousands will swarm the beaches there, he said. A dozen to 20 might pile up on top of each other in one square meter.

Horseshoe crabs mate year-round, but more frequently in March and April, and right now thousands are mating on the south side of the Titusville Causeway east of the Max Brewer Bridge. On Monday and Tuesday, citizen scientists for the FWC Laurilee Thompson and Bill Klein were were logging and tagging horseshoe crabs on the north side of the causeway. They counted 5,000 crabs on the south side of the causeway.

The bleeding process somewhat parallels a blood donation at the Red Cross. They aren't drained, Charles River explains on its website; it takes about 30% of a horseshoe crab's blood. Facilities also won't use a horseshoe crab that is injured or ill. Or too young.

Before the development of LAL, scientists tested the safety of a vaccine, for example, by injecting it into a rabbit. If a rabbit developed a fever or died, they knew the vaccine was unsafe. 

That doesn't mean that all horseshoe crabs, which live 20 to 40 years in the wild, survive the bleeding process. The mortality rate ranges from 3% to 15%. That spectrum takes into account observed mortality and estimates for what might happen after they are released back into the ocean.

How we try to help the horseshoe crab

South Carolina, for example, has some of the strictest and earliest horseshoe crab protections in the country. Since the early 1990s, state law prohibits anyone from even holding a horseshoe crab without a permit.

Floyd said the strict system works, and the horseshoe crab population has been stable or growing for many years. The state keeps count, doing a random survey by trawling annually.

Other regions are not faring as well. New York's stock assessment is poor, says the 2019 report. A throng of reasons contributes to marine animal population decline today, ranging from pollution to loss of coastal habitat from development or the rising seas.

The tough, old horseshoe crab isn't immune from those global forces.

Concern for the horseshoe crab's future spiked in the late 1990s. The red knot shorebird population was declining, signaling trouble on the horseshoe crab front. That's because the migratory birds rely on the horseshoe crab eggs for fuel to fly some 20,000 miles each year.

In the Delaware Bay, as many as a million of the birds will stop to gorge themselves during spawning, often doubling their weight. 

Subsequent regulations and other protections have helped both the red knot and horseshoe crab numbers bounce back. That's not been the case on the other side of the globe.

The Atlantic horseshoe crab's Asian cousins have been decimated in some places, Allen Burgenson said. They do not enjoy the same legal protections, he noted. In Asia, the horseshoe crab is used for medical purposes, bait and are eaten.

When it comes to the conservation effort, the horseshoe crab does have a bit of an image problem. All the things that make it a survivor — that hard covering, the spiky tail, the bright, blue blood — make it not cute and cuddly. 

Burgenson gets it. But he's doing what he can to change people's perspective. He even gave his grand-niece a plush toy version of the horseshoe crab for her crib collection. 

He leads educational lectures as the chair of the horseshoe advisory panel. He speaks to reporters in that capacity, too — as a lot of information about the LAL industry is proprietary and specific horseshoe crab counts for states or regions are kept confidential by law. Later this month, he's doing a Zoom talk about the role of the horseshoe crab in the COVID-19 vaccine.

And, of course, he still is flipping over upside-down horseshoe crabs when he sees them.
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