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Frequently Asked Questions about Gymnodinium catenatum and PSP toxins

What is Gymnodinium catenatum?

Gymnodinium catenatum is a one-cell algal species (dinoflagellate) that forms chains. The alga exists in two forms, a mobile cell and a resting cyst. The mobile cells move using two hairs one around a waist and the other is like a tail. They move up and down the water depths being closer to the surface in the day, and deeper during the night. The mobile cells multiply by asexual division, and often do not separate after this, so are found in chains. Two of these mobile cells can fuse, and then change internally to form a cyst. The cyst is a resting stage that lies in the mud or on seaweed on the sea floor.

Gymnodinium catenatum is able to survive and grow in waters that are lower in temperature than other algae that have historically produced toxic blooms in New Zealand.

The bloom that occurred in New Zealand waters during 2000-2001 survived in water 12-14°C. It is very likely that the organism that NZ has would be able to survive in water temperatures from 12 - 20°C, if it is similar to other temperate strains.

Scientists are not sure what the best environmental conditions are in New Zealand for Gymnodinium catenatum.

How long has Gymnodinium catenatum been in New Zealand?

We do not know how long Gymnodinium catenatum has been in New Zealand. It may be a rare naturally occurring member of our biota or be a new alga here.

What are paralytic shellfish poisoning toxins?

Paralytic Shellfish Poisoning is caused by a group of chemicals called the saxitoxins and gonyautoxins. These chemicals are produced by the algae and released into the shellfish when the algae are eaten. The chemicals all differ in their toxicity to humans, and can be changed depending on the species of shellfish. Stomach acids in animals and humans can also alter the toxicity.

The toxins can also be released into the sea from the algae, as the toxin is soluble in water, but there are no known problems from recreational contact with water.

At what levels of toxicity are people at risk of illness and death?

The risk of illness depends on an individual's genetic make-up such as current state of health, weight, which toxins are present and how much toxin is in the shellfish. The toxins are heat stable so cooking the shellfish will not remove them.

The NZFSA issues warnings to the public when the toxicity is measured at 80ug/100g (saxitoxin equivalent). At this level of toxicity we expect that the toxins will not affect most people. In previous events, levels of toxin have been found at up to 50 times this warning level. Some people have become ill from eating shellfish that were only 10 times above the warning level.

In overseas PSP events caused by Gymnodinium catenatum, people have been put on life support in hospital for up to 10 days and up to 15% of the people who ate affected shellfish died.

What are the symptoms of Paralytic Shellfish Poisoning?

• Numbness and tingling (prickly feeling) around the mouth, face or extremities first.
• Headache and dizziness.
• Moderate to severe symptoms include a spread of the prickly areas, floating feeling, difficulty swallowing and speaking with slight difficulty in breathing and a rapid heart rate.
• Symptoms can progress to dizziness; double vision and paralysis and eventually breathing may stop.

It is possible that these symptoms may take as long as 12 hours to start developing and then may progress rapidly causing respiratory failure within 2 hours. Overseas reports indicate that the affected person is aware of the symptoms throughout and can be quite calm.

If you are ill with these types of symptoms after eating shellfish from any area please consult your doctor immediately and advise health protection staff at your local public health service.

If somebody is seen to have these symptoms and to suffer breathing failure after eating shellfish, rescue breathing and cardiac massage should be given until the person can be put onto artificial respiration.

There is no antidote for PSP toxin and the person has to be kept alive and breathing until the nerves become free of toxin and they are able to recover.

What shellfish are affected?

The species that appears to take in the highest amounts of toxins so far are green-lipped mussels. Other species have been found with toxins that are in the range where illness is possible. These include tuatua, toheroa, oysters, scallops, cockles and pipi. Other species like kina and surf clams should not be taken from the affected areas. Whitebait appears to be unaffected.

Care must be taken when eating paua, crab and crayfish from toxin-affected areas. People should ensure that the gut of paua and crab are removed prior to cooking to avoid the gut and its contents contaminating the meat.

There have been no confirmed reports of illness resulting from eating crayfish. However testing of crayfish from affected areas has shown that the gut can contain PSP toxin. If you take crayfish from affected areas, eat the flesh only - do not eat the gut (or 'gravy').

What precautions need to be taken by the public to help contain the spread of Gymnodinium catenatum algal blooms?

We request that the public do not move water or use potentially contaminated items that could have cells or cysts. The NZFSA also asks that people do not remove young mussels and oysters (spat) from affected areas.

Fishermen and boaties should remove water from the sumps of boats, and wash fishing, scuba and surfing gear. If vehicles have been used on toxin-affected beaches, they should be washed with fresh water, particularly the undercarriage of the vehicle.