5 July 2006

 

Toxic fish poisoning

According to unconfirmed media reports, in June 2006, 16 people were taken ill in Viet Nam as a result of poisoning associated with the consumption of pufferfish [1]. This report and other recent ones of fish poisonings [2], serve to raise awareness of the several types of poisoning that may occur following consumption of fish and shellfish contaminated with toxins.

Pufferfish poisoning

Pufferfish poisoning occurs following ingestion of fish containing tetrodotoxin, a potent neurotoxin. Tetrodotoxin is typically found in pufferfish, porcupine fish and ocean sunfish. These fish are found throughout the Pacific, Atlantic and Indian Oceans. The toxin is concentrated in the ovaries, liver, intestine and skin of these fish and is not inactivated by heating.

In Japan pufferfish or fugu is an expensive delicacy which is eaten for the fugu experience that is characterised by tingling of the lips and tongue, a sensation of general warmth and a feeling of euphoria and exhilaration.  Although improved legislation and licensing of restaurants serving fugu has reduced the incidence, there were 449 cases and 49 deaths of pufferfish poisoning in Japan between 1983 and 1992 [3].

Initial symptoms of pufferfish poisoning include perioral paresthesia, nausea and dizziness within minutes of ingestion. Generalised paresthesiae then develops together with numbness, ataxia, ascending paralysis, headache, vomiting and diarrhoea. In severe cases there is respiratory failure, bradycardia and hypotension. Most deaths occur within six to 24 hours of onset of symptoms and are due to respiratory failure.

There is no antidote for tetrodotoxin; treatment is aimed at limiting the absorption of tetrodotoxin by gastric lavage within the first three hours after ingestion, and intensive management of symptoms.

Ciguatera

Most cases of ciguatera poisoning follow ingestion of coral reef fish containing ciguatoxin and other toxins.  Ciguatoxin originates in algae known as dinoflagellates that are found in association with other algae usually attached to coral reefs. Toxin is ingested by herbivorous fish and becomes concentrated as it progress up the food chain to large carnivorous coral reef fish, and finally to humans. The fish at risk include grouper, snapper, barracuda, jacks, sea bass, and moray eels. Ciguatera is widespread in tropical and subtropical waters, and is most common in the Pacific and Indian oceans and the Caribbean Sea. Ciguatoxin is found in high concentrations in liver, gastrointestinal tract, roe, and fish heads, and is resistant to heat.

Symptoms of ciguatera usually occur within one to four hours of eating contaminated fish, but have been reported within 15 to 30 minutes. Gastrointestinal symptoms of nausea, vomiting and diarrhoea occur early and may be followed by neurologic and, less commonly, cardiac symptoms. Neurologic symptoms include a sensation of hot-cold temperature reversal, paresthesiae affecting the arms, legs, perioral area, tongue and throat, and discomfort in the teeth. Cardiac symptoms can include arrhythmias and hypotension. Death rarely results from cardiac or respiratory failure.

Most symptoms will resolve within one to four weeks with supportive care. However, chronic symptoms of dyesthesias and fatigue may be persistent and will need careful evaluation.

Scromboid

Scromboid fish poisoning follows ingestion of fish that have been inadequately refrigerated allowing the build-up of high levels of histamine in their flesh. Fish that are at risk for this generally belong to the Scrombridae family: bluefin and yellowfin tuna, mackerel, skipjack and bonito. These fish contain high levels of the amino acid histidine in their flesh and as a result of failure to refrigerate fish following catching, histidine is converted to histamine and other scrombotoxins by bacteria at temperatures from 20 to 30°C. Other fish implicated include mahi-mahi, bluefish, sardine, anchovy, herring, and amberjack.

Symptoms of scromboid closely resemble a moderate to severe allergic reaction appearing within 10 to 60 minutes following ingestion. Characteristic symptoms are skin flushing, pruritus, a throbbing headache, dizziness, and nausea, vomiting, abdominal cramps and diarrhoea. Symptoms typically last for several hours.

Management of scromboid involves symptomatic relief using anti-histamines, and most cases resolve within four hours.

 

Paralytic shellfish poisoning

Paralytic shellfish poisoning (PSP) occurs as a result of eating contaminated bi-valve mollusks (clams, oysters, cockles, mussels, scallops) containing saxitoxin and other potent neurotoxins produced by dinoflagellates. Outbreaks may occur in mollusks harvested from both temperate and tropical waters.

Initial symptoms of PSP usually occur within 30 to 60 minutes of eating contaminated shellfish and include paresthesiae of the face, lips and tongue. Other symptoms include headache, nausea, vomiting and diarrhoea. In severe cases ataxia and decreased mental status occur, progressing to flaccid paralysis with respiratory failure over 12 hours. The case fatality rate of PSP varies from 1% to 12%, but persons who survive beyond 12 hours have an improved prognosis.

There is no antidote for PSP and treatment is symptomatic.

Advice for travellers

Neurotoxins responsible for causing poisoning are able to survive normal cooking procedures. In many cases they are also resistant to preservation methods including freezing, canning and smoking.

Many developed areas of the world will adhere to guidelines regarding the harvesting and preparation of fish and shellfish. Warnings may also be posted when conditions are conducive to fish poisonings, such as the presence of excessive amounts of dinoflagellates in breeding areas, known as ‘red tides’. However, less developed countries may not have such guidelines.

Travellers can reduce their risk of toxic poisoning by avoiding potentially contaminated fish and shellfish. Pufferfish should be avoided in all cases, and not eating moray eels and barracuda, as well as avoiding reef fish that weigh three kilograms or more will decrease the risk of ciguatera intoxication. The head, viscera and roe of reef fish should also be avoided. Adequate refrigeration of fresh fish should be maintained until it is prepared for consumption, and will help to prevent scromboid.

Travellers should also be aware that there is a risk of other food and water borne illnesses associated with the consumption of contaminated shellfish, including hepatitis A.

References

1. ProMED-mail. Food poisoning, puffer fish - Viet Nam (Bin Thuan). ProMED-mail 2006; 30 Jun: 20060630.1809. [cited 5 July 2006] http://www.promedmail.org/pls/promed/f?p=2400:1001:

11639032391926977749::NO::F2400_P1001_BACK_PAGE,

F2400_P1001_PUB_MAIL_ID:1010,33403

ProMED-mail. Paralytic shellfish poisoning, human - Viet Nam. ProMED-mail 2006; 21 Jun: 20060621.1717. [cited 5 July 2006] http://www.promedmail.org/pls/promed/f?p=2400:1001:

8492889514027932399::NO::F2400_P1001_BACK_

PAGE,F2400_P1001_PUB_MAIL_ID:1000,33306

3. Ansdell V. Food-borne illness. In: Keystone JS, Kozarsky PE, Freedman DO et al. Eds. Travel Medicine. 2004; 443-451, Mosby 

Further reading

Barbier HM, Diaz JH. Prevention and treatment of toxic seafoodborne diseases in travellers. J Travel Med 2003;10: 29-37.

Mines D, Stahmer S, Shepherd SM.  Poisonings: food, fish, shellfish.  Emerg Med Clin North Am  1997;15:157-77.