The phrasing of this question suggests some misunderstanding of the issue at hand so the answer delves briefly into
- Some basics about the horseshoe crab.
- How horseshoe crabs became an indispensable linchpin for safety testing in present-day biomedicine.
- How the practically unregulated biomedical use of horseshoe crabs harms them and endangers their very future.
- How synthetic alternatives to horseshoe crab blood exist but lack regulatory approval, largely owing to inertia.
Horseshoe crab – Wikipedia blood is an integral component in ensuring the safety of biomedical products intended for contact with our circulating blood and other bodily fluids. A synthetic alternative, recombinant factor C, has existed for years, one that the European Pharmacopeia saw fit to recommend in 2016. Now if only the US Pharmacopeia and FDA followed suit, things would be golden indeed for the horseshoe crab, a surefire and much welcome change of pace for this now extremely beleaguered ancient creature.
Some Basics About The Horseshoe Crab
Actually more closely allied to scorpions and spiders, horseshoe crabs are lucky to make it to maturity by 10 to 12 years of age since a variety of marine organisms prey on their juveniles and only ~3 out of 100000 are estimated to survive past one year (1, 2). That’s actually less horrible than it sounds since each female spawns 100000 eggs at a time, ~20 times per year.
Left to its own devices an adult horseshoe crab, which has few predators other than humans, would live out its life peacefully mucking about in deeper waters along the Atlantic coastline and around Southeast Asia (below from 3), pretty much as nature intended, and every summer arrive onto shores in great numbers to spawn its eggs and breed.
In turn, migratory shorebirds such as the endangered Red Knots feed on these eggs, at the Delaware Bay for example, for sustenance during their annual 9000 mile-long marathon expeditions from the southernmost tip of South America to the Canadian Arctic. Such shorebird predation on their eggs helps keep the horseshoe crab populations in check, an integrated process as is the wont when the natural order of things prevails.
One might surmise that things must have proceeded in this vein for eons. After all, the fossil record suggests that this Living fossil – Wikipedia has remained virtually unchanged for hundreds of millions of years, since the days of the dinosaurs in fact, an odd little factoid that’s deeply humbling or at least it ought to be.
Unfortunately, two forms of ruthless and deadly human predators of horseshoe crabs showed up, one of which is indeed present-day biomedicine and the other whelk and eel fishers who use them as bait, voraciously so at one point to the tune of millions annually in the US alone for example (4). Don’t we already know the beginning, middle and end of the epitaph for planet earth, the one that goes, “human, the apex predator”? Ask the horseshoe crab. It knows since several of its species, lushly abundant just a few generations back, are now listed as either endangered or critically endangered.
How Horseshoe Crab Blood Became An Indispensable Linchpin For Safety Testing In Present-Day Biomedicine
Many unpleasant realities abound all around us that each one of us doesn’t necessarily haven’t to take on and wrestle with personally. Human society routinely throws up plentiful horrors that represent predicaments of such colossal scale that glossing over them the best one can seems the easiest option since the effort to manifestly change such systems is simply too overwhelming for any single individual. For example a vegan could say that they’ve made an ethical choice so the unbearable abomination and pain of factory farming is on others. Problem is there’s no escaping the horseshoe crab issue for anyone.
Like it or not, horseshoe crab blood helps ensure the safety of virtually every injectable drug and biomedical device available today. How we treat these ancient denizens is everyone’s business because we’ve made them indispensable for our biomedical safety these days and the life of any one of us may one day depend on this involuntary munificence of the horseshoe crab whether we acknowledge it or not. Here’s how.
Go to the doctor, get tested, get treatment. Needle, pacemaker, catheter, injectable drug, all sorts of surgeries, all sterile of course – at this point in our history we just take these and so many more relatively recent medical innovations for granted. We’ve come to expect any sort of injectable that comes in contact with our blood as it circulates within our body to be safe and to not send us into a death spiral of inflammation from an ingrained over-reaction to bacterial contamination.
The predicament with such an expectation is that it’s practically unrealistic since we live in a microbial world and not only do they live all around us and even within us, getting rid of their products is practically impossible as well. Specifically, Lipopolysaccharide – Wikipedia, pieces of skin of gram-negative bacteria if you will, which are everywhere and stubbornly disinclined to easy riddance.
After all this world belongs to microbes and we came along much later with a pronounced technological bent that automatically lends itself to tinkering and solutioneering of the sort that’s simply antithetical to the way nature operates. Taking blood out, putting it back in, injecting all manner of substances into it, invasive surgeries, transplants – in the blink of an eye, we humans invented and now take for granted such procedures and products that are categorically outlandish from nature’s perspective and yet many if not most among us expect them as a matter of course without really understanding the contortions necessary to ensure their safety.
Even though LPS is also called endotoxin or pyrogen (fever-inducing) in lay terms, it isn’t a classic toxin in the conventional sense. After all, plenty of LPS-laden gram-negative bacteria live lifelong within our guts too. It’s just a quirk of nature that when in the blood, LPS as well as many other bacterial products of its ilk provoke the sort of extremely strong immune response that can itself be life-threatening, the sort that often kills people from septic shock for example, not because such bacterial components themselves cause terrible damage when in blood but because our immune system tends to stereotypically over-react to them when they wind up in certain amounts in circulating blood.
How to ensure then that whatever we inject into our blood or stick into our bodies has levels of LPS far below those that trigger such cataclysmic responses? That’s where the now-unwittingly benighted horseshoe crab and more specifically its distinct blue blood come in (below from 5).
The Limulus amebocyte lysate – Wikipedia is used to detect extremely small amounts of LPS, which are ubiquitous in the environment and yet lethal if they get into the bloodstream in sufficient doses. Turns out the horseshoe crab’s blood cells, amebocytes, are exquisitely sensitive in detecting LPS – they contain enzymes that clot and immobilize endotoxins (6, 7) – and this is why the FDA requires injectables and medical equipment to be tested for safety with LAL tests (below from 8),
“The purified LAL has the capability of detecting one millionth of a billionth of a gram of endotoxin in less than 1 h (Mikkelsen, 1988).”
Over recent decades as global healthcare needs ramped up precipitously, the process of using horseshoe crab blood for safety testing spread from the US to Asia and LAL tests morphed into LAL/TAL/CAL, so named after the respective horseshoe crab species, Limulus polyphemus for LAL in the US, and Tachypleus tridentatus and Tachypleus gigas for TAL and Carcinoscorpius rotundicauda for CAL in Asia.
How The Practically Unregulated Biomedical Use Of Horseshoe Crabs Harms Them And Endangers Their Very Future
Predation that long ago spilled over into depredation, the entirely one-sided relationship of humans with horseshoe crabs has proven all too toxic for them even as it began by happenstance as such things often do. The numbers speak for themselves (below from 9),
“Ever since the FDA’s authorization, the use of horseshoe crabs for LAL production by the pharmaceutical industry has increased progressively. The number of crabs being bled increased from 130,000 in 1989 to 260,000 in 1997. By 2010, over half a million crabs were bled annually. Horseshoe crab blood is estimated a value of $15,000 per quart, according to the National Oceanic and Atmospheric Administration.
The simplicity, accuracy and sensitivity of its antimicrobial and anticarcinogenic reaction have made the horseshoe crab an exceptional species for biotechnology research. The expediency of this crab is demonstrated by its widespread application for responsive sensing of endotoxins, uropathogens, bacteriuria, fungal infections and sepsis in the health care industry.”
And indeed the value of horseshoe crab blood has increased even more since even that 2015 assessment (below from 10),
“Such is the demand that processed lysate from the crab’s blood is now, gram for gram, one of the most valuable liquids on Earth, with a reported price between $35,000 and $60,000 per gallon.”
Adult horseshoe crabs are typically bled of ~30% of their blood at a time and then released back into the water. While US sourcing companies claim mortality rates of ~<15% on average from these bleeds, skepticism about such self-reporting is warranted because the bleeding process for biomedical use is essentially unregulated in many if not most parts of the world and actual rates may be even as high as 50 to 75% to altogether 100% (below from 11).
“Few people understand how deeply the TAL/LAL industry affects the lives of nearly every man, woman, child and domestic animal in the world, who are dependent upon medical service for their health. The safety of much of the world’s pharmaceutical and medical devices must be tested for the presence of life-threatening endotoxins prior to public use, and the most reliable endotoxin detection test currently available is TAL/LAL. There is no indication that the world’s human and animal population will become less dependent on medical services in the years to come. In fact, as our global population expands, ages, and medical advancements improve and/or prolong life, we expect to become more, not less reliant upon endotoxin detection methodologies, which currently means TAL or LAL. It is questionable whether current harvesting levels for TAL/LAL can be sustained, much less meet the projected future demands of this rapidly growing market, particularly if Asian horseshoe crab species are harvested to functional extinction… Approximately 25% of the medical device market is currently dependent upon TAL/LAL for endotoxin detection.”
Desperate for a silver lining at this point? I certainly am. Remember fishermen, the other apex human predators of horseshoe crabs? Turns out US commercial harvesters sued the US government to continue harvesting horseshoe crabs in protected waters and lost. As a result harvesting for bait has declined precipitously in the US (below from 12, figure below from 13),
“…the government’s win resulted in the prohibition of horseshoe crab harvest for any reason in the National Seashore and in the Monomoy National Wildlife Refuge (actually a ban was instituted for the refuge until a new compatibility study could be completed) (Compatibility Determination Eastern Massachusetts National Wildlife Refuge Complex 2002). The ruling eventually resulted in a ban for the harvesting of horseshoe crabs in all federal waters (James-Pirri 2012).”
Problem is this stricture left the LAL industry specifically untouched (below from 12).
“To further protect the LAL industry that used far fewer crabs than the bait industry, and since mortality from bleeding was considered insignificant (most bled crabs were returned to their environment alive), the biomedical industry was exempt from restrictions on harvesting horseshoe crabs with the exception of a requirement to report the number of horseshoe crabs bled (ASMFC 1998; Novitsky 2009). The extremely small number of horseshoe crabs harvested specifically for research is considered inconsequential and taking for research purposes is completely exempt…
Today, there are four companies operating in the United States that produce LAL from Limulus polyphemus harvested from various locations along the Atlantic Coast. It should be noted that there exists a similar industry in Southeast Asia where other species of horseshoe crabs, namely Tachypleus tridentatus, Tachypleus gigas, and Carcinoscorpius rotundicauda are, or can potentially be used to make an [sic] LAL equivalent, Tachypleus amebocyte lysate (TAL) and Carcinoscorpius amebocyte lysate (CAL).”
Problem also because regulatory oversight of horseshoe crab use in Southeast Asia is practically non-existent (below from 11).
“Presently, the growth of the global healthcare industry is entirely dependent upon the harvest and collection of blood from live horseshoe crabs to produce TAL/LAL. Although direct mortality of horseshoe crabs due to LAL production is estimated to be relatively low, 8–15 % (Rudloe 1983 ; Walls and Berkson 2003), the mortality associated with TAL production is 100 % because after bleeding, the animals are sold to secondary markets for food and chitin production.”
Problem also because horseshoe crabs harvested for biomedical bleeding are no longer inconsequentially fewer in number. In fact, harvesting for bleeding has expanded in the US to now ~equal harvesting for bait (below from 5),
“…new oversight agencies were established to mediate the risks from over-harvesting, and restrictions were placed on the number of horseshoe crabs collected for bait in order to regulate populations. These agencies further generated programs for stock management, developed state quota regulations, and established best practices for biomedical harvesting. In 2015, 583,208 horseshoe crabs were harvested as bait for eel and whelk (Atlantic States Marine Fisheries Commission, 2016), a significant reduction from the millions that were once harvested (Atlantic States Marine Fisheries Commission, 2013)…
The Atlantic States Marine Fisheries Commission (ASMFC) reported that in 2015, 559,903 horseshoe crabs were transported to biomedical facilities for the production of LAL (Atlantic States Marine Fisheries Commission, 2016).”
Problem also because the biomedical industry has been strikingly incurious about the impact of bleeding on long-term horseshoe crab health. Catch ’em, bleed ’em, throw ’em back – that’s been the expedient motto of this coerced, wantonly cruel and vampiric transaction (below from 14).
Vitality of crabs released after they’re bled isn’t guaranteed at all. In fact, extremely skewed ratios in favor of males were suspected for many years and only confirmed by definitive studies since just 2010 (15, below from 12; tables from 11 and 16). Female crabs are much bigger than males meaning much larger blood volumes which is why they get bled predominantly.
“Early studies indicated that it took at least a week for the crab to regain blood volume and several weeks to regain baseline amebocyte counts (Anderson et al. 2013). Since it is impractical to maintain crabs in holding ponds until they regain blood volumes and cell count, a practice of one bleed per year became the norm. Although bled crabs were seldom tagged, a fresh scar or needle puncture mark on the arthrodial membrane was quite apparent so that even if a bled crab was recaptured in the same year, a trained technician could avoid a second bleeding if a scar was in evidence. However, there is no provision in the proposed BMPs [Best Medical Practices] for preventing crabs being bled twice or more during a single season, and the effect on crab mortality is unknown. Likewise, due to the design of the horseshoe crab’s circulatory system (open, i.e. no separate veins with capillaries connected to the arteries to circulate hemolymph back to the cardiac sinus), once the cardiac sinus (large tubular heart) and 11 major arteries (Shuster 2003) are empty, the blood flow slows to a drip or stops completely. It has been estimated that no more than 30% of the entire blood of an individual crab is ever removed using a gravity flow as opposed to vacuum aspiration (Novitsky 1991). This type of bleeding, i.e. using gravity flow, appears to have become an industry standard (Levin et al. 2003), but due to the secrecy associated with the biomedical industry and a lack of a provision in the BMPs, it remains unclear whether this method is used universally.”
The fewer females that survive bleeds, the fewer progeny in succeeding years so no wonder horseshoe crabs decline not just from harvesting for bait but also from long-term morbidity and mortality from bleeds.
To be useful is a good thing we are taught. Trust us to then turn around and ensure that too much of a good thing is an unfortunate fate as well since that is precisely the curse we humans have visited upon the poor horseshoe crab. When it comes to unbridled ambition and avarice, we can be counted on to never disappoint as this poor creature has now discovered to its own peril – a literal blue blood literally paying with its life for its blue bloodedness courtesy us capricious humans.
How Synthetic Alternatives To Horseshoe Crab Blood Exist But Lack Regulatory Approval, Largely Owing To Inertia
(below from 12).
“ there is no reason why a synthetic replacement for LAL cannot be designed. In fact, one LAL manufacturer currently sells a synthetic substitute along with a traditional LAL (Lonza 2014). This synthetic substitute was invented by scientists using one of the horseshoe crab genes responsible for the main enzyme component of LAL to engineer a reagent produced in yeast (Ding et al. 1977). According to the FDA however, this synthetic reagent is not by definition, LAL, i.e. a lysate (L) of Limulus (L) amebocytes (A) and thus cannot be licensed. The major users of LAL, the pharmaceutical industry (various lots of intravenous solutions, biologics, and medical devices are required to be tested with FDA-licensed LAL prior to release for distribution and use) do not have a choice of using a synthetic substitute until the FDA changes regulations. It is interesting to note that LAL may be one of only a few diagnostic reagents (if not the only one) that is regulated on its composition (LAL) rather than what it detects (endotoxin). As endotoxin has been standardized as to its toxicity (pyrogenic dose in humans), and an official reference standard is commercially available and accepted by several pharmacopeias and the FDA, any reagent that can accurately and routinely detect the pyrogenic dose of endotoxin, i.e. by testing with the reference standard, should be a ready substitute for LAL. The PyroGene TM synthetic reagent already does this (Lonza 2014), as do some other endotoxin tests currently under development or that have been described in the literature, such as the in vitro pyrogen test (Daneshian et al. 2006). Thus all those concerned with horseshoe crab conservation, especially state agencies responsible for the regulation of horseshoe crab harvest and the ASMFC [Atlantic States Marine Fisheries Commission], should actively encourage the FDA to allow LAL substitutes as long as the substitutes can be properly validated (i.e., shown to detect a pyrogenic level of endotoxin in an actual pharmaceutical drug and device).”
Ready for another silver lining at this point? I know I certainly am. Relatively meager and inadequate though they may yet be, the regulatory oversights that have developed in the US for horseshoe crab harvesting since the 1990s suggest that sustained effort to educate and create awareness (below from 17, 18) could go a long way in helping reverse their currently routine, expedient, ruthless and unsustainable exploitation. Now the need of the hour is to get widespread regulatory approval for synthetic alternatives for LAL/TAL/CAL, which would really do the trick in stemming at least the harm from increasingly unsustainable biomedical overuse.
1. Botton, Mark L., Robert E. Loveland, and Athena Tiwari. “Distribution, abundance, and survivorship of young-of-the-year in a commercially exploited population of horseshoe crabs Limulus polyphemus.” Marine Ecology Progress Series 265 (2003): 175-184. https://www.int-res.com/articles/meps2003/265/m265p175.pdf
2. Carmichael, Ruth H., Deborah Rutecki, and Ivan Valiela. “Abundance and population structure of the Atlantic horseshoe crab Limulus polyphemus in Pleasant Bay, Cape Cod.” Marine Ecology Progress Series 246 (2003): 225-239. http://www.int-res.com/articles/meps2003/246/m246p225.pdf
3. Horseshoe Crab – Barrier Island Ecology UNCW
4. Smith, David R., Michael J. Millard, and Ruth H. Carmichael. “Comparative status and assessment of Limulus polyphemus with emphasis on the New England and Delaware Bay populations.” Biology and conservation of horseshoe crabs. Springer, Boston, MA, 2009. 361-386. https://www.researchgate.net/profile/John_Tanacredi/publication/291233650_Biology_and_Conservation_of_Horseshoe_Crabs/links/59c913560f7e9bd2c01a4c20/Biology-and-Conservation-of-Horseshoe-Crabs.pdf#page=366
5. Krisfalusi-Gannon, Jordan, et al. “The role of horseshoe crabs in the biomedical industry and recent trends impacting species sustainability.” Frontiers in Marine Science 5 (2018): 185. The Role of Horseshoe Crabs in the Biomedical Industry and Recent Trends Impacting Species Sustainability
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8. Walls, Elizabeth A., Jim Berkson, and Stephen A. Smith. “The horseshoe crab, Limulus polyphemus: 200 million years of existence, 100 years of study.” Reviews in Fisheries Science 10.1 (2002): 39-73. https://www.researchgate.net/profile/Stephen_Smith42/publication/252068789_The_Horseshoe_Crab_Limulus_polyphemus_200_Million_Years_of_Existence_100_Years_of_Study/links/0deec531ccf00733b6000000/The-Horseshoe-Crab-Limulus-polyphemus-200-Million-Years-of-Existence-100-Years-of-Study.pdf
9. Das, A. P., B. Bal, and P. S. Mahapatra. “Horseshoe Crabs in Modern Day Biotechnological Applications.” Changing Global Perspectives on Horseshoe Crab Biology, Conservation and Management. Springer, Cham, 2015. 463-474.
10. This crab could save your life – if humans don’t wipe it out first
11. Gauvry, Glenn. “Current horseshoe crab harvesting practices cannot support global demand for TAL/LAL: The pharmaceutical and medical device industries’ role in the sustainability of horseshoe crabs.” Changing global perspectives on horseshoe crab biology, conservation and management. Springer, Cham, 2015. 475-482. http://horseshoecrab.org/press/2018/11/Current-Horseshoe-Crab-Harvesting-Practices-Cannot-Support-Global-Demand-for-TAL-LAL.pdf
12. Novitsky, Thomas J. “Biomedical implications for managing the Limulus polyphemus harvest along the northeast coast of the United States.” Changing Global Perspectives on Horseshoe Crab Biology, Conservation and Management. Springer, Cham, 2015. 483-500.
13. Kreamer, Gary, and Stewart Michels. “History of horseshoe crab harvest on Delaware Bay.” Biology and conservation of horseshoe crabs. Springer, Boston, MA, 2009. 299-313. https://www.researchgate.net/profile/John_Tanacredi/publication/291233650_Biology_and_Conservation_of_Horseshoe_Crabs/links/59c913560f7e9bd2c01a4c20/Biology-and-Conservation-of-Horseshoe-Crabs.pdf#page=306
14. The Last Days of the Blue-Blood Harvest
15. The Blood of the Crab
16. Owings, Meghan. “Effects of the biomedical bleeding process on the behavior and physiology of the American horseshoe crab, Limulus polyphemus.” (2017). https://scholars.unh.edu/cgi/viewcontent.cgi?article=2152&context=thesis
17. Kreamer, Gary, and Sharon W. Kreamer. “Green Eggs & Sand, Team Limulus, and More: Educating for Horseshoe Crab Conservation in the United States.” Changing Global Perspectives on Horseshoe Crab Biology, Conservation and Management. Springer, Cham, 2015. 557-574.
18. Gauvry, Glenn, and Ruth H. Carmichael. “Young Voices: Through the Arts, Future Environmental Stewards Have a Global Voice.” Changing Global Perspectives on Horseshoe Crab Biology, Conservation and Management. Springer, Cham, 2015. 587-593.