July 1, 2010
Canadian scientists have developed a powerful new method for detecting paralytic shellfish poisoning (PSP) toxins — the most common cause of shellfish-related illness in coastal nations.
Called LC PCOX (liquid chromatographic post-column oxidation), the method can provide an earlier warning of PSP contamination than the standard test used by most countries around the world. It will allow seafood inspectors to "closely watch the shellfish in a particular growing area so they can shut down harvest before PSP levels exceed regulatory limits," says Dr. Michael Quilliam, the lead researcher at the NRC Institute for Marine Biosciences (NRC-IMB) in Halifax.
According to Dr. Quilliam, the standard test (a mouse bioassay) has been used since the 1950s. This method involves injecting an extract from shellfish into a mouse and then recording if and when the animal dies. "The mouse bioassay is a very good test," he stresses. "It has very few false negatives, which means it can protect people quite well."
Dr. Michael Quilliam (standing) and CFIA guest worker Ryan Gibbs at the NRC Institute for Marine Biosciences in Halifax. In 2010, the Food Inspection Group in Dartmouth (including Gibbs) won a President’s Award from CFIA for developing and implementing the LC PCOX method in collaboration with NRC.
So why fix what isn't broken?
The problem is that the mouse test can barely detect PSP toxins at the "set regulatory level" — that is, the minimum level at which shellfish are considered unsafe to eat. "What we want to do is detect toxins as soon as they start to build up in shellfish," says Dr. Quilliam. With less sensitive tests, seafood exporters risk shipping shellfish that is slightly over the regulatory level and then having hundreds of thousands of dollars worth of product destroyed.
Another problem with the bioassay is that it requires mice. "There are tens of thousands of mice being sacrificed around the world each year to keep seafood safe," says Dr. Quilliam. Under increasing pressure from animal rights groups, a few European countries began banning the mouse bioassay in the 1990s, which meant that alternative detection methods were required. "NRC was ahead of the game as we have been developing new chemical analysis methods for shellfish toxins since 1987," he adds.
NRC researchers in Halifax produce calibration standards and reference materials for toxin analysis in laboratories around the world.
Studies by NRC and its partner in the project, the Canadian Food Inspection Agency, (CFIA), show that the LC PCOX method "is just as good at detecting PSP toxins as the mouse bioassay and gives slightly fewer false alarms," says Dr. Quilliam. It is also faster and less costly for large batches of tests, as well as being more sensitive.
Over the next few months, CFIA plans to dramatically reduce the number of mouse bioassays it performs while introducing the LC PCOX assay at all shellfish inspection labs across Canada. Elsewhere, the mouse bioassay will continue to be used until NRC and CFIA complete an international validation study, which will allow the new method to be accepted worldwide, says Dr. Quilliam.
In a related initiative, NRC and CFIA have worked closely over the last few years to develop a range of certified reference materials (CRMs) for PSP toxins that are essential to fully implement the LC PCOX method. NRC's CRM program is the only one of its kind in the world and distributes CRMs to more than 40 countries.
Paralytic shellfish poisoning (PSP) toxins are the most common and dangerous family of marine biotoxins found around the world. PSP toxins are produced by microscopic algae in seawater that periodically form dense blooms and then die off. PSP toxins can accumulate in clams, mussels, scallops and oysters on a seasonal basis. The shellfish toxins are periodically detected in shellfish from the north and west coasts of Canada and in the Bay of Fundy.
Symptoms of PSP illness include tingling and numbness of the lips, tongue, hands and feet, as well as difficulty swallowing. In extreme cases, exposure to these toxins can lead to muscle paralysis, respiratory paralysis and death. Thanks to PSP monitoring programs, paralytic shellfish poisoning is very rare today, although it still strikes hundreds of people around the world each year — especially in remote locations.
