Pity the poor mice that ensure the mussels and oysters we eat are safe. If the shellfish being tested for toxins is clean, the mice live, if not, they die.
EU regulations require that tests for the presence of toxins - particularly those which arise during algal blooms and concentrate in shellfish - be done using mice. "Toxins have to be measured in shellfish throughout the year," explained Mr Tony Forde who is heading the work at the National Diagnostics Centre, based at UCG and part of BioResearch Ireland. "EU legislation requires that this be carried out using a proscribed mouse bioassay."
These assays are done on campus under contract from the Marine Institute. Oysters, mussels, cockles, clams and other shellfish are checked for producers from all along the western seaboard. The tests indicate the presence of any toxins. The one most commonly found is okadaic acid, a by-product of algal blooms which causes diarrhoetic shellfish poisoning in humans.
This is an uncomfortable, rather than dangerous illness, but other bloom toxins can cause death. Saxitoxin, found in Canadian and Japanese waters, causes paralytic shellfish poisoning which can be fatal. Domoic acid, found in blooms in North American waters, causes amnesic shellfish poisoning.
Gastrointestinal tracts from shellfish are collected and concentrated, and injected into the mice. "If the toxin is not present, nothing happens. If it is, they either get sick or they die," Mr Forde explained.
It can't be much fun for the mice, hence the interest in developing assays that do not require the unfortunate test rodents. The two-year project, financed by the Marine Institute, has just got under way with two postgraduate researchers and the collaboration of Dr Marion Boland of Trinity College.
The group is concentrating on two tests, one giving a rapid response if the toxin is present, and a more comprehensive test which uses animal cells in vitro to measure toxin levels.
"We are trying to develop a quick test, for example a dipstick screening test that can be used on site," Mr Forde explained. It involves laying down a substrate on to which the enzyme, phosphatase, can be fixed.
Samples are first mixed with a test solution and then applied to the enzyme dipstick. The phosphatase reacts with the solution, changing colour if no toxin is present, but this reaction is blocked if okadaic acid is in the sample.
Testing for levels of toxin using cultured cell lines is a much more complex process. The toxin will change or kill off cells and these morphological changes can be detected using a microscope.
However, another system under study repeats the process of mixing a sample with a test solution that is then put in contact with the cells. The goal would be to establish a scale of expected change in growth, physiology or cell death rate based on the level of toxin present.
The dipstick test could be used on site but the cell line tests would have to be carried out under much more controlled laboratory conditions, Mr Forde explained. There are also the EU regulatory aspects of these testing procedures, which must remain independent in order to protect human health.