AIMS solves mystery poison puzzle

An Australian researcher at the Australian Institute of Marine Science (AIMS) has solved the medical mystery of the death of an East Timorese man from what appeared to be poisoning in late 2000.

Alison Robertson, a PhD student in AIMS' marine biotechnology group, has discovered that the man died of paralytic shellfish poisoning as a result of eating a crab that carried saxitoxin, a deadly poison listed on the UN's chemical weapons schedule.

The poison is produced by the red algal tidal blooms and also by blue green algae in fresh water, and is also found in a number of crab species in the tropics.

"We had a pretty good idea from the forensic report and the details of his death," said Robertson. The man had apparently died within three hours of eating a crab caught on a local beach.

Although there have never been cases of paralytic shellfish poisoning in Australia, Robertson said the potential was there.

"People need to be alerted to the danger of eating tropical crabs and other shellfish," she said. "The lack of cases could be due to the misdiagnosis of seafood allergies instead of saxitoxin poisoning, as the symptoms are very similar and until recently, there has not been a portable method to test for the toxin."

Symptoms include tingling and numbness of the mouth, tongue and face, often with nausea and vomiting. Severe cases lead to death due to paralysis of the cardio-respiratory system.

In Australia, commonly eaten crabs including mud, sand or spanner crabs do not carry saxitoxin, but quite a few of the tropical crabs do. According to Robertson the pretty ones are often the most toxic.

But Robertson and her supervisor Dr Lyndon Llewellyn said that no one knew how the crabs carried the deadly toxin.

"This is the big mystery - they are not filter feeders. They must have a different source of the toxin," said Llewellyn.

"No one knows whether the crabs get the toxin from the food they eat, or whether they [or bacteria within them] might produce it themselves," explained Robertson.

Shellfish, like oysters and mussels, are filter feeders and pick the algal toxin up from the water, but the crabs are active feeders. They also tend to be poisonous all the time, rather than just at times of algal blooms, she explained.

Spin-off developing toxin detector

Llewellyn said that saxitoxin contamination was a major issue for shellfish farmers. His team has developed a sensitive bioassay for detecting the toxin in seafood and drinking water, which is now being developed for commercial release by AIMS and James Cook University spin-off company Toxitech.

The current approved test in seafood is a mouse test that relies on the mouse dying to establish the presence of saxitoxin. There is no test available for saxitoxin in drinking water.

According to Toxitech CEO Dr Brett Kettle, about 98 per cent of the market for a saxitoxin test is overseas, primarily in the drinking water market. "We think it is worth in excess of $100 million per year," he said.

The test is being developed in two forms, as a biosensor unit and as a strip test. Toxitech hopes to field test a prototype of the biosensor unit in November, according to Kettle.