The Hong Kong Centre for Health Protection (CHP) of the Department of Health is investigating a suspected ciguatera poisoning case affecting a 38-year-old man. The patient, with good past health, developed symptoms of ciguatera poisoning including facial and tongue numbness, skin itchiness over the forehead and the neck, abdominal pain and diarrhoea about two to three hours after eating a marine fish at home on September 24.
He attended the Accident and Emergency Department of Pamela Youde Nethersole Eastern Hospital on September 25 and was subsequently admitted. He is now in stable condition. The CHP’s investigations are ongoing.
Ciguatera fish poisoning is not uncommon in tropical areas. More than 400 species of fish have been implicated in this food borne illness that’s relatively common in several areas of the world. This toxin is the result of the accumulation of marine algae and the toxins they produce passing up the food chain. These marine algae hang on to dead coral and seaweed. They are then eaten by herbivore fish which are subsequently eaten by predatory reef fish which concentrates the toxin in its tissue.
The toxin accumulates in the fish body, in particular in internal organs, through eating small fish that consumed toxic algae in coral reef seas. A larger fish is therefore more likely to carry higher amounts of the toxin. However, it is not easy to tell from the appearance of the fish whether it contains the toxin. The reef fishes are more likely to get contaminated during storms and other turbulence.
People affected may show symptoms of numbness of the mouth and the limbs, vomiting, diarrhoea, pain in the joints and muscles. An unusual characteristic that is common in ciguatera is temperature reversal. This may be seen from 2 to 5 days after eating the fish. Hot objects seem cold and cold objects can give a shock-like sensation. There have been serious injuries because a person was unable to recognize extremely hot sensations. Other odd symptoms are food may taste metallic and teeth may seem painful or loose.Most people affected by ciguatoxin would recover without long-term health effects, but if excessive toxins are consumed, the circulatory and nervous systems can be affected.
Symptoms may come back after ingesting certain foods and drinks; alcohol, caffeine, nuts and fish.
There are no laboratory tests to diagnose this disease and it’s based on clinical symptoms and a history ofeating an offending fish.
Ciguatera fish poisoning 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.
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.
The toxin cannot be destroyed by cooking. To prevent ciguatera fish poisoning, you should observe the following measures:
* Eat less coral reef fish;
* Eat small amounts of coral reef fish at any one meal and avoid having a whole fish feast in which all the dishes come from the same big coral reef fish;
* Avoid eating the head, skin, intestines and roe of coral reef fish, which usually have a higher concentration of toxins;
* When eating coral reef fish, avoid consuming alcohol, peanuts or beans as they may aggravate ciguatoxin poisoning;
* Seek medical treatment immediately should symptoms of ciguatoxin fish poisoning appear; and
* Coral reef fish should be purchased from reputable and licensed seafood shops. Do not buy the fish when the source is doubtful.