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By Dr Eddy Bajrovic, Medical Director of Travelvax Australia

Were Queensland mother and daughter, Noeline and Yvana Bischoff, who died in Bali on Saturday, the victims of food poisoning linked to a meal of fish?
According to media reports, police in Bali are investigating food the pair shared at lunch at a restaurant in Ubud and later at dinner at the Buddha Bar and Restaurant, which is attached to the Padang Bai Beach resort in the eastern regency of Karangasem.

The 53-year-old nurse from the Sunshine Coast and her 14-year-old daughter died within hours of reportedly eating several dishes, including a reef fish called mahi mahi (dolphin fish). A white-fleshed species, mahi mahi has a similar texture and taste to flounder.
Autopsies on the pair will now be conducted in Australia, however there has been speculation this week that if the fish was responsible for their deaths the cause was either ciguatera or one of the other toxins found in certain reef fish, or scombroid poisoning, a foodborne illness that results from eating spoiled fish.
Both are among the more common forms of seafood poisoning worldwide, although there are a raft of other infections linked to seafood. These can be caused by a variety of bacteria, viruses, and parasites, as a 2010 paper published in the Clinical Microbiology Reviews journal explains.
However, the symptoms of illness caused by these pathogens are rarely so rapid or so severe.
Adequate cooking kills most disease-causing agents in food. However, unlike meat and poultry, that are usually fully cooked, seafood is often consumed raw or prepared in ways that do not kill disease-causing organisms.

Scombroid ‘mimics’ allergic reaction

Of the two main ‘suspects’ in the Bischoffs’ deaths, scombroid poisoning is most commonly linked to mahi mahi, mackerel, tuna, bluefish, bonito, sardines, anchovies, and related species that were inadequately refrigerated or preserved after being caught. Scombroid infection is often missed because its symptoms closely resemble those of an allergic reaction (which was initially suggested as the cause of death of the Bischoffs).
The toxic agent most commonly implicated in scombroid poisoning is histamine, which is derived from histidine. The fish implicated in scombroid poisoning have flesh that contains naturally high levels of histidine.
The histidine is converted to histamine by the effects of bacterial overgrowth when fish have not been properly refrigerated and stored. This histamine and other scombotoxins are not destroyed by normal cooking temperatures, so even properly cooked fish can be affected.
However, the fact that of all the diners at the restaurant only the Bischoffs became ill suggests that a single fish containing ciguatera or a similar biotoxin may have been responsible.

Ciguatera biotoxin ascends food chain

Despite underreporting, ciguatera fish poisoning (CFP) now is considered one of the most common illnesses related to eating fish. The incidence in travellers to highly endemic areas has been estimated as high as 3 per 100, according to information from America’s Centers for Disease Control and Prevention (CDC).
An average 50,000 cases are reported worldwide annually and CFP occurs across the Pacific basin, the Indian Ocean (including Indonesia) and the Caribbean, the CDC says.
Ciguatera poisoning generally is believed to be confined to coral reef fish in water between the latitudes of 35 degrees N and 35 degrees S. Species of fish most frequently implicated include groupers, amberjack, red snappers, eel, sea bass, barracuda, coral trout, and Spanish mackerel.
While CFP is associated with eating fish caught in tropical or semitropical waters, the CDC says increased global marketing of these species has increased the chances of fish-lovers in temperate zones becoming ill.
Scientists also warn that warming seawaters might expand the ranges of ciguatoxin-contaminated fish. Newly recognised areas of risk include the Canary Islands, the eastern Mediterranean, and the western Gulf of Mexico.

Toxin is impossible to detect

Ciguatera toxin is produced by microscopic, single-celled algae that live on the surface of coral. Small, plant-eating fish eat the algae and, in turn, are eaten by larger meat-eating fish.
When these large predatory reef fish are caught and eaten by people, they also consume the fish’s accumulated biotoxin.
At least 5 types of ciguatoxin have been identified and are known to accumulate in larger and older fish higher up the food chain.
Fish heavier than 2kg may contain significant amounts of toxin and readily produce toxic effects when eaten.
The poison is impossible to detect without testing: Its presence does not affect the smell, colour, or taste of the fish.
Ciguatera is also very heat stable: boiling, steaming, or frying the fish will not diminish or eliminate it. It will even withstand human gastric acid.

Consult local fishermen on CFP risk

The majority of coral reefs are not ciguatoxic: outbreaks of ciguatera are usually very localised and local fishermen are the best people to consult about the risk posed by reef fish in the area.
There is no known antidote for the poison, which usually results in less severe symptoms of headaches, vomiting, dizziness and fatigue. However, in extreme cases, it can cause neurological damage – even death.
Readers recall our article on New Zealand woman, Amanda Austrin, who experienced ciguatera poisoning when she ate coral trout wrapped in banana leaves and cooked over an open fire on a beach in Fiji in 2012. The bitter taste from just one bite made her spit out the fish, but within hours her face, body and limbs began to tingle before going numb – classic symptoms of ciguatera poisoning.
For most sufferers, the symptoms last only a few days. However, they can last many, many months and be severe – as in Ms Austrin’s case, which was reported by the New Zealand Herald.

More facts on ciguatera fish poisoning (CFP)

With thanks to the WHO and the CDC, here are some things fish-loving travellers should know to avoid the risk of ciguatera fish poisoning.

What causes CFP? The main toxic dinoflagellate (algae or plankton) that causes ciguatera fish poisoning is Gambierdicus toxicus. It is found primarily in sub-tropical and tropical regions where it lives with other algae on dead coral.

Where is CFP found? Toxic fish have been found in Indonesia, as well as the Pacific and Indian Ocean regions, and in tropical areas of the Caribbean.

Which fish are toxic? There’s no comprehensive list of non-ciguatoxic fish and it is impossible to determine if fish from a reef are safe without testing. Between 300 and 400 species of fish have been implicated in ciguatera fish poisoning. And, a species that is ciguatoxic in one area may be safe in another. It is the location where a fish is caught rather than its species which determines whether it is ciguatoxic.

What are its symptoms? The initial symptoms are similar to any other food poisoning – abdominal pain, nausea, vomiting, and diarrhoea. CFP may occur anywhere from 10 min to 24 hours after eating toxic fish. The most common neurological symptoms are tingling and numbness in the mouth and the extremities, and muscle cramping. One unusual symptom is the sensation of temperature reversal – a sensory inversion whereby hot or warm objects feel cold, and cold objects may feel warm.

How long do they last? Only rarely is ciguatera fatal. The overall death rate is 0.1% but this varies depending upon amount of toxin consumed and proximity to effective medical care. Neurological symptoms generally last a few days to several weeks, but chronic neuropsychiatric symptoms and fatigue have been known to persist for months.

What should you do? If you experience symptoms after eating reef fish, see a doctor as soon as possible. There is no single specific remedy for ciguatera fish poisoning. The most successful management involves supportive and symptomatic treatment, including inducing vomiting. (Try to obtain, pack and freeze portions of the fish for analysis to help confirm the diagnosis.)
As mentioned, local fishermen are generally the best source of information on whether CFP is known to occur in a particular area, and which species may be implicated.
The rule is: in the absence of reliable information, avoid eating large reef fish.

Read more about ciguatera fish poisoning (WHO).

Get expert advice on the health risks that may be associated with your next overseas trip by calling Travelvax Australia’s free travel health advisory service on 1300 360 164.