10 September 1993 The Shellfish Toxicity Crisis - Many Lessons for the Future

Dr Ravi Gooneratne, a Lincoln University toxicologist stresses the immediate need for New Zealand to set up research programmes to characterise and identify 'early clues' of toxic algal blooms so that appropriate regulatory actions can be initiated quickly when needed, to minimise the impact on public health and protect the country's overseas markets.

Most New Zealand shellfisheries are open again after the horrible situation the industry experienced a few months ago, and it is now time to reassure the public of the safety of shellfish products and boost consumer confidence.

The shellfish industry has learnt that there is "life after shellfish toxins", and many overseas markets, used to dealing with such events, are most likely to remain open to trade in shellfish from New Zealand. The recent problem underlines the vulnerability of our primary industries to disease and the need for quick reaction by the authorities to any hint of health problems to protect our overseas selfish exports now worth over $80 million.

Prior to this year, no official recorded cases of human shellfish poisoning in New Zealand existed, although there are records of several fish and sea bird deaths associated with algal toxins dating back to the 1860's. Very little research on algal toxins had been done in New Zealand, so it took some time and a major effort to identify the organisms and toxins which were responsible for the recent shellfish poisoning. Marine organisms produce many toxic substances, but only a few are involved in human food poisoning.

Many different animals have evolved with the ability to produce toxins to help them survive. They use toxins to kill or paralyse their prey, or to defend against predators. Shellfish (clams, mussels, crabs, scallops, lobster) are a little different. The toxins are not produced by the creatures themselves but it is a food they eat, a type of algae called dinoflagellates, that contain the toxin. The majority of dinoflagellate algae are harmless but a few can be toxic. The toxin builds up in the shellfish when they feed on the toxic ones. Although the recent cases of shellfish poisoning have been attributed somewhat glibly to pollution, this is an over-simplification of the problem. Many other factors contributed to the recent outbreak.

Algae produce more toxin in warm weather and when their own food supply is plentiful. Last year, a series of events occurred that encouraged the development of toxic algae in coastal waters.

Throughout most of 1992, coastal water temperatures were low compared to the long-term average. However, in December temperatures rose rapidly. Such oceanographic temperature patterns and the availability of nutrients such as phosphates, nitrates and other pollutants in run-off from coastal lands, probably favoured the rapid reproduction of toxin-producing algae. This created a "bloom" or high concentration of algae in December and in the following few months. Some of the toxin producing dinoflagellates were identified in New Zealand waters for the first time ever. It is possible that these new toxic dinoflagellates were discharged into New Zealand waters in ballast from visiting ships.

Some algal blooms are red, and known as "red tide" or "red water". The colour is due to a pigment called peridinin. Shellfish feeding in "red water" can accumulate the toxin with apparently no toxic effect to themselves, but they are quite toxic to the humans who eat them. We were fortunate that the New Zealand outbreak of poisoning was not as severe as elsewhere. Many serious cases of human illnesses have been reported from North America, Canada and France with several deaths reported from the Philippines in the last 2 years.

Several different toxins are produced by different dinoflagellates and hence several disease syndromes are associated with shellfish poisoning. These include:

• Brevetoxins causing Neurotoxic shellfish poisoning (NSP).
• Okadaic acid causing Diarrhoeic shellfish poisoning (DSP).
• Saxitoxins causing Paralytic shellfish poisoning (PSP).
• Domoic acid causing Amnesic shellfish poisoning (ASP).

The major toxicity syndrome identified in the 1993 New Zealand outbreak was Neurotoxic shellfish poisoning (NSP) caused by brevetoxins produced by the dinoflagellate Gymnodinium breve. Previous reported outbreaks have been from Florida and North Carolina in USA. Signs of poisoning show up about 4 hours after consuming toxic shellfish. The effects of this toxin include muscle weakness, headaches, muscle and joint pains, diarrhoea, vomiting, but the most characteristic feature is the difficulty in distinguishing between hot and cold.

It is also likely that a few incidents of Diarrhoeic shellfish poisoning (DSP) were seen in New Zealand this year. DSP is caused by the toxin okadaic produced by the Dinophysis species. As the name indicates this toxin causes diarrhoea and stomach cramps, nausea and vomiting. So it can easily be mistaken for a stomach upset. Illness appears in generally less than 12 hours after eating toxic shellfish.

The other 2 toxic syndromes Paralytic shellfish poisoning (PSP) and Amnesic shellfish poisoning (ASP) were probably not seen in New Zealand this year. But PSP is a common occurrence in shellfish toxicity syndromes in most other countries. It is caused by saxitoxin family of poisons produced by Alexandrium and Gonyaulax species. The effects of this toxin in humans include a floating and a tingling feeling, numbness in the lips, face and neck, nausea, vomiting, diarrhoea, and difficulty in walking because of an effect on the muscles. The symptoms appear very quick within minutes after eating. Death from paralysis of the muscles used for breathing has occasionally been reported overseas. Amnesic shellfish poisoning (ASP) is caused by toxin domoic acid produced by Nitzchia species. The disease syndrome is characterised by memory loss (that may be permanent), diarrhoea, vomiting and stomach pain.

The authorities who handled the investigations in New Zealand, the Ministry of Agriculture and Fisheries, Institute of Environmental Health and Forensic Sciences, New Zealand Communicable Disease Centre, National Institute of Water and Atmospheric Research, and Cawthron Institute should be commended for an excellent job done under a crisis situation. Recently at a shellfish workshop in Wellington Dr Peter O'Hara (MAF) aptly described this year's shellfish toxicity episode as a 'crisis' because:

• there were many human illnesses consistent with shellfish toxicity
• regulatory authorities were faced with an event for which they were not prepared for
• there were several toxins and several types of diseases which made regulatory decisions difficult
• the commercial shellfish industry sustained severe economic damage
• there was major impact on local and export markets (although it is now recovering).

There are many lessons to be learnt from the New Zealand poisoning episode. Now we know we have toxic dinoflagellates in our coastal waters, the commercial shellfish industry and the occurrence of toxic blooms will have to co-exist. But it requires research and a reliable monitoring programme to enable authorities to better manage future events. More specifically we need to:

• know the environmental and oceanographic temperature patterns that can alert us to a likely toxic bloom, toxin production by algae and toxin accumulation by shellfish
• develop on-going surveillance and monitoring programmes to identify toxic algal blooms
• know how long it takes different types of shellfish to get rid of the toxin(s) (it now appears that scallops take a longer time)
• have a cost-effective quality assurance monitoring programme of shellfish products
• know whether we can get rid of toxins from toxic shellfish without affecting their taste (steaming and immersion in ozone have been tried but that seems to alter the taste)
• develop toxin identification tests which are specific, sensitive, rapid and reliable
• have legislation to prevent the discharge of ballast water near New Zealand coastal waters
• develop a coherent research effort to gather information as quickly as possible and make sensible public health decisions and show our credibility to seafood customers both locally and overseas.

The implementation of these measures – and most essentially the research and monitoring programmes – should allow harvesting controls to be put in place before unsafe levels of toxins occur. If that is done, then the likelihood of human poisonings will be reduced and hopefully eliminated. It's definitely a matter of being wise before the event.

Dr Ravi Gooneratne is a Senior Lecturer in Toxicology in the Animal and Veterinary Sciences Group at Lincoln University. He was the Lincoln University representative at a recent Workshop on "Marine toxins and New Zealand shellfish" held in Wellington under the auspices of The Royal Society of New Zealand.

Dr Ravi Gooneratne, Senior Lecturer, Animal and Veterinary Sciences Group, Lincoln University, Canterbury, New Zealand.

Ian Collins, Journalist, Lincoln University, Canterbury, New Zealand.