Vol. 21 No. 5 November 2001

In September last year shellfish on the west coast of the North Island became affected after ingesting toxins from the marine algae Gymnodinium caternatum.

People who ate mussels, pipi, tuatua and cockles were most likely to be affected, but paua, kina, scallops and oysters could cause illness too.

New Zealand shellfish have been monitored for the presence of marine biotoxins since 1993, after about 180 people suffered from neurotoxic shellfish poisoning. This kind of poisoning is caused by chemicals called saxitoxins and gonyautoxins which are produced by algae and permeate the shellfish when the algae is eaten.

The same Gymnodinium overseas has put people on life support in hospital, and one outbreak killed 15% of those who ate the affected shellfish. Poisoned people first feel numbness and prickly tingling around the mouth or face, hands and feet. Next comes headache and dizziness, with the “prickly” areas spreading. In bad cases there can be a floating feeling, difficulty in swallowing and speaking, rapid heart rate, difficulty in breathing.

Life-threatening cases will have double-vision and paralysis leading to breathing stopping. One authority ranks Paralytic Shellfish Poisoning toxin ninth in the list of deadly toxins found in nature.

As well as Paralytic Shellfish Poisoning (PSP) there is also Diarrhoetic Shellfish Poisoning (DSP) and Amnesic Shellfish Poisoning (ASP) – all known by their initials.

DSP, as you can guess, causes extreme gastro-intestinal upset. It is less serious than PSP but nevertheless can kill through dehydration and rare complications.

The agent which causes ASP, domoic acid, binds to receptors in the brain and causes their dysfunction. Poisoning symptoms begin with gut upset, rapidly followed by dizziness, disorientation and memory loss – which often persists indefinitely. It can be fatal to humans, but often kills marine mammals. Poisoning from eating fish which had eaten algae rich in domoic acid killed more than 400 Californian sealions in 1998.

A lot of toxic algae in the water can affect swimmers, but not as severely as eating toxic seafood. About 90 people were affected by algal bloom in Wellington Harbour in November 1998. That particular bloom, of Gymnodinium, also killed a lot of Wellington’s marine life. In February 1998, 185 swimmers and beach-walkers at two Wairarapa beaches complained of headaches, irritated nose, eyes and skin, and coughing. Dogs were affected too, and dead fish were washed up on the shore.

Cooking shellfish or fish that have ingested a toxic variety of algae does not destroy the poison; neither does freezing or drying.

As well as shellfish, marine fish, especially barracuda and coral-reef fish, may be toxic from algae eating. The fish themselves look okay, and there is no test outside a sophisticated laboratory to determine if they are safe.

This kind of fish poisoning is called ciguatera fish poisoning; bacteria thrive on raw fish and produce nasty toxins, too – this bacterial poisoning is called scombroid poisoning.

Ciguatera poisoning shows itself within six hours after consumption of toxic fish, and includes perioral numbness and tingling (paresthesia), which may spread to the extremities, nausea, vomiting and diarrhoea. Neurological signs include intensified paresthesia, arthralgia, myalgia, headache, temperature sensory reversal (hot feels cold, cold feels hot) and acute sensitivity to temperature extremes, vertigo, and muscular weakness to the point of prostration. Cardiovascular signs include arrhythmia, bradycardia or tachycardia, and reduced blood pressure.

Ciguatera poisoning is usually self-limiting, and signs of poisoning often subside within several days from onset. However, in severe cases the neurological symptoms are known to persist from weeks to months.

In a few isolated cases neurological symptoms have persisted for several years, and in other cases recovered patients have experienced recurrence of neurological symptoms months to years after recovery. Such relapses are most often associated with changes in dietary habits (nuts and shellfish are blamed) or with consumption of alcohol. There is a low incidence of death resulting from respiratory and cardiovascular failure.

Fish like the fugu puffer fish are naturally toxic, whether exposed to algae or not – but fugu poisoning (tetrodotoxic poisoning) can be the subject of a future article.

One victim of algal bloom in New Zealand was an American in his fifties who came here for a film-crew job with Lord of the Rings, but became too sick to work after eating toxic mussels gathered at Piha, on the Tasman Sea coast, near Auckland, in June 2000.

For about 10 days he had symptoms like very bad flu – waves of chill, then fever; diarrhoea; delirium with a lot of agitated talking. When this subsided his arms felt dead and there was great pain in his shoulders in general and the shoulder joint in particular.

He was very debilitated, still in pain, and his mind was so foggy he was reliant on friends to a large extent when he consulted a homœopath in mid August.

He was prescribed Strychninum phosphoricum (for the muscle pain associated with contracted musculature of shoulder area) initially. This greatly reduced the pain and he was then able to give a clearer description of the initial attack. Based on this information he was given Karwinskia humboldtiana which removed most symptoms, but head pain with sore muscles in the occipital region became pronounced – for which he got Curare.

In November, when he was virtually symptom-free, except not as physically robust as before the ill-fated meal, he was given Withania somniferum 6x as, for want of a better word, a tonic, and as an aid to restful sleep.