Skip to main content
Part of complete coverage on

Why this crab's blood could save your life

By Kieron Monks, for CNN
September 4, 2014 -- Updated 1046 GMT (1846 HKT)
Nearly 50 years ago, scientists discovered the horseshoe crab's clotting-response to bacterial toxins. Now, its blood is harvested in huge quantities, to be used in a test to ensure medical products are not contaminated. Nearly 50 years ago, scientists discovered the horseshoe crab's clotting-response to bacterial toxins. Now, its blood is harvested in huge quantities, to be used in a test to ensure medical products are not contaminated.
HIDE CAPTION
Life-saving crab
Prehistoric species
Blue blood
Harvesting crabs by hand
Crabs return to the sea
Endosafe Portable Test System (PTS)
Endosafe in Space
<<
<
1
2
3
4
5
6
7
>
>>
STORY HIGHLIGHTS
  • Horseshoe crab blood can detect and trap bacterial toxins
  • Its blood is harvested for a test to ensure medical products are not contaminated
  • Up to 600,000 crabs are captured each year for their blood
  • Between 10-30% of donor crabs die in the process

Vital Signs is a monthly program bringing viewers health stories from around the world.

(CNN) -- During World War Two, soldiers learned to fear treatment as much as enemy bullets. Unsanitary conditions and equipment in field hospitals made open wounds a breeding ground for bacteria that killed thousands, particularly the fast-acting and barely detectable gram-negative strains that caused toxic shock syndrome, meningitis, and typhoid.

Today, vast improvements in medical hygiene have greatly reduced the odds of patients being poisoned on the treatment table. And our safety is protected by an unlikely source -- the bright blue blood of the horseshoe crab.

The helmet-shaped creature has developed a unique defense to compensate for its vulnerability to infection in shallow waters. When faced with toxins produced by bacteria, amebocyte cells in the blood -- colored blue by their copper-based molecules -- identify and congeal around the invading matter, trapping the threat inside a gel-like seal that prevents it from spreading.

Nature's method is now utilized on a grand scale. Over 600,000 crabs are captured each year during the spring mating season, to "donate" around 30% of their blood in a handful of specialist facilities in the United States and Asia. The blood is worth $60,000 a gallon in a global industry valued at $50 million a year.

Read: The people with someone else's face

Detection is down to one part per trillion. But we can take it down to a tenth of a trillion.
John Dubczak, Charles River Laboratories

An extract has been used in the industry-standard limulus amebocyte lysate (LAL) contamination test since the 1970s -- replacing a rabbit-based system. Forty-five minutes of exposure to the crab's blood is enough to reveal endotoxins from gram-negative bacteria which otherwise avoid detection, and is sensitive enough to isolate a threat the equivalent size of a grain of sand in a swimming pool. The U.S. Food and Drug Administration (FDA) requires that intravenous drugs and any medical equipment coming in contact with the body must first pass through the crab's blood, from needles to surgical implants including pacemakers. As a result, thousands more of us survive such procedures.

The method is established but undergoes constant improvement, according to John Dubczak, General Manager at Charles River Laboratories, which manufactures and globally distributes LAL products.

"Detection is down to one part per trillion," he said. "But we can take it down to a tenth of a trillion, and further orders of magnitude more sensitive."

Charles River has adapted the system into a more resource-efficient, handheld kit requiring as little as 5% of the blood solution. Such systems can be applied outside the lab and break new frontiers, such as on a trip the International Space Station.

The 'bionic eye'
Can this cure cancer?

"The test was used to determine if certain types of bacteria were present on various space station surfaces," said Norman Wainwright, the facility's director of Research and Development. Further, the system could "help perform biological studies necessary for an extended human presence in space, from crew health and spacecraft environmental studies to the search for life elsewhere in the solar system."

Read: These 8 whiz kids are the future of medicine

The blood is finding other uses on Earth too. Japanese scientists have devised a test for fungal infections with it, and further research is developing anti-viral and anti-cancer treatment through the same principle of isolating and trapping threats.

As the applications and their value multiplies, efforts have increased to develop alternative tests, rather than rely on harvesting the crabs. One approach uses an electronic chip that provides an alert when in contact with contaminants. Another system using liquid crystals, developed by the University of Wisconsin-Madison, could offer similar detection ability at lower cost.

The blood is crucial for human health issues but the biomedical industry needs to keep the population steady.
Christopher Chabot, biology professor, Plymouth State

"The (Wisconsin) literature claims to surpass the sensitivity and specificity for finding toxins, so false positives are not a serious problem," says Dr. Peter B. Armstrong, a professor of molecular and cellular biology at the University of California. "But nothing has gone to the level of FDA approval to show it is yet a viable alternative to LAL test. Knowing the cost and difficulty of obtaining FDA tests, it may be some time before any alternative is out there on the market."

The urgency may increase with reports of horseshoe crab numbers declining, for a variety of reasons, with the world's largest population in Delaware Bay reportedly reduced by between 75% and 90% in the last 15 years. Although there are welfare procedures in harvesting the blood, between 10-30% of donor crabs die in the process. One recent study showed that survivors are also impaired after release and often incapable of mating, further threatening the population.

"It's difficult because the blood is crucial for human health issues but the biomedical industry needs to keep the population steady," says Christopher Chabot, a biology professor at Plymouth State, who led the study. "We suggest decreasing the time they are out of water, and maintaining an ambient temperature for transportation ... there is a lesser mortality rate if you keep them cool."

Ultimately, Chabot believes an alternative is necessary to reduce the strain on the population, through both conservation programs and the development of a synthetic substitute. It is not clear what expiry date there is on the lifesaving services of the horseshoe crab, but without it medicine faces a return to the dark ages.

Read: The people with someone else's face

Read: These 8 whiz kids are the future of medicine

Read: Hunting down 'fiery serpent' disease

ADVERTISEMENT
Part of complete coverage on
April 24, 2014 -- Updated 1002 GMT (1802 HKT)
A device for extracting water from air is being used by the military -- could it help developing countries too?
May 23, 2014 -- Updated 0931 GMT (1731 HKT)
Air-cleaning pavillion to be launched at the 2015 Milan Expo
Air pollution is now the biggest global environmental killer, but these high-tech solutions could save lives.
April 14, 2014 -- Updated 1954 GMT (0354 HKT)
robohand metal hand
A South African carpenter lost his fingers in an accident -- now he's making mechanical fingers and hands for others.
August 7, 2014 -- Updated 1216 GMT (2016 HKT)
Connie Culp was injured when her husband shot her in 2004. She underwent a near-total face transplant at the Cleveland Clinic in 2008 -- the first operation of its kind in the United States
As face transplants become more common, hospitals may soon be asking: Will you donate your face?
May 28, 2014 -- Updated 1718 GMT (0118 HKT)
TB is growing increasingly drug resistant -- and it's becoming a global problem.
August 14, 2014 -- Updated 1249 GMT (2049 HKT)
A 10-year-old inventor and a 20-year-old MD? Meet the whiz kids changing the face of medicine.
May 9, 2014 -- Updated 1027 GMT (1827 HKT)
A Southern Sudanese man uses a pipe filter to protect himself from Guinea worm disease while drinking water from a potentially infected source. The pipe filter strains out the water fleas that can contain Guinea worm larvae.
Guinea worm disease once infected millions -- now it's almost eradicated. But can we catch the final cases?
September 4, 2014 -- Updated 1046 GMT (1846 HKT)
A staff member from the Environment & Animal Society of Taiwan, a non-profit organisation based in Taipei, points at the part of a horseshoe crab where blood is drawn for use in laboratory tests against animals, during a press conference in Taipei on December 4, 2012.
Hundreds of thousands of horseshoe crabs are captured each year for their incredible blue blood. Here's why.
September 12, 2014 -- Updated 1127 GMT (1927 HKT)
Lika Rose Caticon, 7, who is suffering from Typhoid fever, holds a doll as she lies in a makeshift cot at the overcrowded JP Rizal Memorial District Hospital in Calamba City south of the Philippine capital Manila on March 5, 2008.
As we travel ever further afield, which infectious diseases do you need to know about?
vital signs logo
Vital Signs is a monthly program bringing viewers health stories from around the world.
ADVERTISEMENT