Food Safety Focus (84th Issue, July 2013) – Incident in Focus

Ciguatoxin Poisoning and Coral Reef Fish

Reported by Dr. Dawin LO, Medical & Health Officer,
Food Incidents Response & Management Unit,
Centre for Food Safety

There has been a recent report of a ciguatoxin food poisoning (CFP) case which affected a number of people who had consumed coral reef fish. Ciguatoxins are one of the common forms of neurotoxins causing food poisoning in Hong Kong. This article describes the local situation of CFP and provides advice to the public and the trade on the prevention of CFP.

Ciguatoxins

Ciguatoxins are a group of heat-stable and fat-soluble compounds produced by the marine plankton Gambierdiscus toxicus. They bioaccumulate up the food chain, starting with herbivorous fish that graze on toxic marine planktons in the coral reef, then successively accumulate in the body of larger carnivorous fish and finally in humans. They are up to 50 to 100 times more concentrated in the viscera and gonads of the affected fish, while the fish has no symptom and also cannot be identified by its appearance, taste, texture or smell. The toxins are heat-stable and cannot be removed by cooking or processing.

Initial symptoms of CFP can appear as short as 30 minutes after consumption of ciguateric fish. The symptoms can be gastrointestinal or neurological. Gastrointestinal symptoms like vomiting, diarrhoea, nausea and abdominal pain usually last only a few days. Neurological symptoms like tingling of lips, hands and feet, skin itching, change in temperature perception, fatigue, muscle and joint pain appear later and last for longer time. Sensitivity of an individual to CFP intoxication could be increased due to factors like previous CFP episode, consumption of alcoholic beverages, nuts and seed products.

Local Situation of CFP

CFP is the most common form of neurotoxin poisoning associated with the consumption of fish in Hong Kong. From 2000 to 12 June 2013, the Centre for Food Safety had received 284 referrals of CFP from the Department of Health (see Figure). A total of 867 persons were affected.

Figure: Number of ciguatoxins cases from 2000 to 2013 (Up to 12 June 2013)

The reporting of CFP occurred year round. However, it was observed that over 60% of total cases were reported in March to July of the year. The number of person affected also provided similar observation.

Different kinds of coral reef fish caught in the wild were known to be associated with CFP. Black fin red snapper, Tiger grouper, Lyretail, Leopard coral grouper, Areolated coral grouper and Moray eel were the top six common types of fish linked to CFP, accounting for over 50% of CFP cases. Farmed fish which was usually fed by formulated pellet or trash fish was not likely the source of toxins.

Fish commonly involved in CFP from 2000 to 12 June 2013.

Ciguatoxins bioaccumulate up the food chain, the larger the fish the higher the concentration of ciguatoxins. The fish involved in CFP is usually greater than 2 kg (3 catties) but occasionally fish less than this weight had also been reported. Source tracing revealed that the most frequently at-risk contaminated fishing grounds are the Nansha Island, South Pacific and Hainan Island.

Key Points to Note:

• CFP is the most common form of neurotoxin poisoning associated with the consumption of coral reef fish in Hong Kong.
• Fish containing ciguatoxins cannot be identified by its appearance, taste, texture or smell.
• The larger the coral reef fish, the more likely ciguatoxins may be present and at higher concentration.

Advice to the Public

1. Consume less coral reef fishes in terms of frequency and the amount consumed in each meal.
2. Avoid eating the head, viscera, skin, and roe of coral reef fish which usually have higher concentration of toxins.
3. When eating coral reef fish, alcohol, peanuts or beans should be avoided.
4. Persons who have previous CFP episode should refrain from eating coral reef fish.
5. Seek medical treatment immediately when symptoms of CFP appear.

Advice to the Trade

1. Avoid sourcing fishes from areas known to be at risk of ciguatoxins.
2. Adhere strictly to the Food Safety Ordinance in record keeping.