Horseshoe crabs are fascinating sea creatures that have been around for 450 million years. Known for their horseshoe-like shape, these ancient animals have a unique blue blood that plays an important role in modern medicine. The reason behind their blue blood is the presence of copper, which is carried in a protein called hemocyanin.
In the 1960s, scientists discovered that the blood of horseshoe crabs clots when it comes into contact with bacterial toxins. This discovery led to the development of Limulus Amoebocyte Lysate (LAL). It is a substance used to test medical products for contamination. Despite the existence of synthetic alternatives, the use of horseshoe crab blood continues, especially in the U.S. It’s even played a vital role in ensuring COVID-19 vaccine efforts. Let’s dive into the details.
What’s Special About Horseshoe Crab Blood?
Horseshoe crab blood is milky-blue due to hemocyanin, a copper-based protein that transports oxygen. But blue blood is not all that’s special about the Horseshoe crabs. In 1956, Fred Bang, a medical researcher noted another unique characteristic. He found that the blood contains cells called amebocytes, which detect bacterial endotoxins. When the crab blood interacts with endotoxin, the prehistoric cells in the blood clots and form a solid mass.
Bang soon recognized that these cells were a part of the crab’s ancient immune system. More importantly, he knew that this could help in detecting deadly bacterial contaminants.
These endotoxins can be deadly if they enter vaccines or other sterile medical products. LAL (Limulus Amoebocyte Lysate), derived from horseshoe crab blood, is essential for testing these products. The cost of this blood is also incredibly high, about $60,000 per gallon.
“All pharmaceutical companies around the world rely on these crabs. When you think about it, your mind is boggled by the reliance that we have on this primitive creature.”
Barbara Brummer, state director for The Nature Conservancy in New Jersey.
Harvesting Horseshoe Crab Blood
After the scientists figured out how to use the amebocyte lysate, they used it to test drugs and vaccines. The U.S. Food and Drug Administration also approved horseshoe crab lysate usage in 1977.
Each year, pharmaceutical companies collect about half a million Atlantic horseshoe crabs. They bleed the crabs and return them to the ocean. However, some don’t survive. This practice, along with overharvesting for fishing bait, has significantly reduced horseshoe crab populations.
In Delaware Bay, a prime egg-laying spot, the number of spawning crabs dropped from 1.24 million in 1990 to about 335,211 in 2019. The blood extraction process involves capturing the crabs, extracting their blood near the heart, and releasing them back into the ocean. Unfortunately, 10% to 15% of the crabs do not survive.
Role in COVID-19 Vaccine Development
During the COVID-19 pandemic, horseshoe crab blood played a critical role in testing vaccines and related medical equipment. The LAL test, based on horseshoe crab blood, ensures that products are free of Gram-negative bacteria, which are both common and lethal.
Every antibody test, vaccine batch, syringe, and vial used during the pandemic was tested with LAL. Billions of COVID-19 vaccine doses and around 600,000 tests were performed with lysate produced and drained within a single day by the manufacturing companies.
“This places no undue burden on the [lysate] supply chain or horseshoe crab populations.”
Dubczak, executive director of reagent development and pilot program operations.
Horseshoe Crab’s Evolutionary Journey
Horseshoe crabs have remained almost unchanged for hundreds of millions of years. Despite their name, they are more closely related to spiders and scorpions than to crabs. These creatures have nine eyes, two of which are compound eyes, and seven are simple eyes. Their stability and minimal evolutionary changes over millions of years make them a remarkable species.
Delaware Bay Stopover To Lay Eggs!
The harvesting of horseshoe crabs has a significant impact on their populations, especially in areas like Delaware Bay. This reduction affects various species that rely on horseshoe crab eggs for food, such as red knots and diamondback terrapins.
Red knots, migratory shorebirds, depend on these eggs to fuel their long journeys from South America to the Arctic. During their stopover in Delaware Bay, red knots nearly double their body weight by consuming horseshoe crab eggs. However, the decline in crab populations threatens this vital food source, leading to a drop in red knot numbers from 40,000 in 2019 to just 30,000 recently.
Ethical and Conservation Concerns
The increased demand for horseshoe crab blood during the pandemic has further threatened their populations. Conservationists are exploring alternative methods to reduce dependency on wild horseshoe crabs and are advocating for the wider adoption of synthetic alternatives like rFC.
In 2016, a synthetic alternative to the substance, recombinant factor C (rFC), received approval in Europe. Some U.S. drug companies also started using it. However, its safety remained unproven.
Efforts are also underway to protect horseshoe crab populations and ensure the sustainability of their use in medical science.
Conclusion
Horseshoe crabs play an essential role in medical science, particularly in ensuring the safety of vaccines and other medical products. While their blood is invaluable, the ethical and environmental concerns surrounding its use cannot be ignored. The potential for synthetic alternatives offers hope for reducing the environmental impact. Sustainable practices and conservation measures are crucial to protecting horseshoe crab populations and maintaining their ecological role.
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