Shellfish poisoning caused through algal toxins

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What is an algal toxin?

An algal toxin is a poison produced by some types of algae.

What are algae?

Very small one celled plants which float in the sea that form part of sea plankton. They are smaller than a pin head in size and invisible to the naked eye.

Which algae are dangerous?

Some members of the "dinoflagellate" group are known to produce toxins. A dinoflagellate is a single cell algae which is propelled by two tiny tails.

How does toxin produced by tiny plankton harm human beings?

Shellfish such as mussels feed by filtering seawater and can absorb toxins from the algae in their gut. The shellfish themselves are not usually harmed, but if people eat them, they can be affected.

Most affected people have suffered from feelings such as numbness or tingling in the tongue, face or tips of fingers and toes. Difficulty in swallowing, double vision, clumsiness, drowsiness and muscle pain are also effects. Some people overseas have died from toxic shellfish poisoning.

What should I do if I think I have toxic algal poisoning?

Go to your doctor and get in touch with the health protection staff at your local district health board. For the Waikato area (stretching from Mokau to Port Waikato on the West Coast, and covering the Coromandel Peninsula):

• Telephone: (07) 838 2569 or freephone 0800 800 977

It is important to let the district health board know about all cases of poisoning as toxic shellfish poisoning is a notifiable disease.

What is being done about it?

A monitoring programme has been put in place to test samples of shellfish for algal toxins. Samples obtained from commercial marine farms and recreational shellfish gathering areas are tested in a laboratory in Auckland. Areas of coastline are closed for shellfish harvesting when the level of toxin exceeds the safety level.

An area can be re-opened for gathering shellfish after:

• three "clear" weekly samples with no evidence of toxins; and
• no notification of illness caused by people eating shellfish from the area; and
• a plan is in place for continued sampling in the area to check whether a toxin has reappeared.
  

Aren't shellfish supposed to be safe to eat if we keep them cold and then cook them properly?

It is always important to do this to protect against bacteria which may contaminate shellfish. However these measures do not get rid of any toxins that the shellfish may have.

Shellfish available from retail outlets are only permitted for sale if they have been obtained from shellfish farms that have been "cleared" and reopened.

How do I find out which areas are safe for the harvesting of recreational shellfish?

Health protection officers, are able to advise which areas are safe for the harvesting of shellfish, as these people are the co-ordinators of the algal surveillance programme and are aware of areas where the bacterial quality of shellfish are safest. Notices advising the public against harvesting are placed in areas like beaches and boat ramps where unsafe levels of toxin have been identified in the shellfish.

More information

• Further information is available from the Public Health Unit on Telephone (07) 838 2569.
• The New Zealand Food Safety Authority website also has information on marine biotoxin closures.
  

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