University of Queensland researchers have developed a detection method for a toxin responsible for around 25,000 food poisoning cases in the world each year.
Ciguatera affects around 100 Queenslanders each year following their consumption of warm water fish contaminated with a class of highly potent ciguatoxins.
The method developed by Centre for Drug Design and Development (3D Centre) and Queensland Department of Primary Industries (QDPI) researcher Dr Richard Lewis and head of the Centre's mass spectrometry laboratory Alan Jones is believed to be the world's first analytical test using state-of-the-art mass spectrometry rather than animal models (bioassays).
Scientists believe ciguatoxins enter the marine food chain by attaching to algae which are then eaten by herbivorous fish and in some instances, shrimp. Despite its potency in humans - people can experience poisoning from toxicity levels as low as 0.1 parts per billion - the toxin can remain in fish for years without any apparent effect.
Symptoms of ciguatera can persist for a few weeks or many months and include nausea and vomiting, aching joints, muscle pains, weakness, itching sensations and tingling and numbness of the lips, hands and feet. One of the most distinctive symptoms is an alteration of temperature sensation, where cold objects often give a burning or dry ice sensation.
In parts of the world where ciguatera occurs frequently such as the atoll islands of the Pacific, the disease creates a major strain on health services and productivity.
In Australia, ciguatera mainly strikes in Queensland following consumption of reef fish including coral trout and Spanish mackerel.
Dr Lewis and Mr Jones developed the analytical test using latest technology and pure toxin samples. The QDPI sample is one of only two supplies of pure toxin in the world.
'Good toxin supplies are vital for any assay development. A lot of ciguatera studies end up as inconclusive because researchers cannot obtain enough reference toxin for experiments,' Dr Lewis said.
The Lewis-Jones test can be adapted to detect ciguatoxins from Indian Ocean, Pacific Ocean and Caribbean Sea fish even though each area's toxin varies slightly in structure. Dr Lewis said the test's enhanced sensitivity towards the toxin's presence in Pacific fish was fortunate as these toxins were far more potent than those found elsewhere.
The liquid chromatography mass spectrometry (LC/MS/MS) method developed by the researchers involves the analysis of a lipid extract from a few grams of fish.
'Toxin is distinguished on the basis of its molecular weight and retention time compared to standards spiked into the samples,' Dr Lewis said.
Dr Lewis said while the method was currently too expensive to be used routinely at industry or personal level, it provided an ideal tool for checking the effectiveness of rapid, cheaper assays as they became available.
Dr Lewis has been studying ciguatera for a decade in collaboration with staff from the QDPI. He first began investigating the disease for his PhD with the University's Zoology Department, completed in 1985 and supervised by former Professor Bob Endean.
He was instrumental in introducing Queensland doctors to an effective mannitol-based treatment for ciguatera in 1990. Using data from the Marshall Islands, Dr Lewis and Child Health Department Professor John Pearn ran a Queensland-based clinical trial of the therapy.
Mannitol, an inert sugar, was administered to patients intravenously and once effective dosages were established, was found to be highly successful in treating the disease if patients received early diagnosis, Dr Lewis said.
'It is thought the toxin causes a swelling around nerve cells resulting in the neurological symptoms such as the tingling and aching sensations. Mannitol appears to relieve this swelling,' he said.
'Mannitol treatment is still not widely recognised among doctors and not all doctors know about ciguatera. Ciguatera is often mistaken for other health problems and left undiagnosed and therefore untreated.'
For more information, contact Dr Lewis (telephone 3365 1924).
