EVANS HEAD – What was once considered a tropical food poisoning danger is now becoming a problem in places much further south.

And it could be another symptom of global climate change.

Heidi Hollis was working at an RSL Club in Evans Head on the northern NSW coast back in February when she and several colleagues tucked into a lunch of Spanish mackerel.

What followed was months of pain as food poisoning-like symptoms initially sent her to hospital for several days and left her with persistent nerve damage.

“I was unable to walk until a week ago,” Hollis said.

The source of the ailment, though, was much worse than a standard dodgy meal. Rather it was triggered by toxins contained in certain fish that are difficult to detect and can’t be destroyed by cooking.

Known as ciguatera fish poisoning, the illness has been mostly a tropical problem. Early Pacific explorers described it as far back as 1606 and even in 1776 during the second voyage of James Cook.

More than 1500 cases have been documented in Australia since 1965 and the number appears to be rising.

The toxins are produced by marine microalgae, particularly the gambierdiscus genus.

As fish graze on the algae and are then eaten by other fish, toxins accumulate up the food chain to levels harmful to humans.

This year, NSW had its first cases of the illness from fish caught in the state’s waters, with Food Authority NSW documenting four at Evans Head – including Hollis – and Scotts Head, also in the state’s north.

Researchers, including Shauna Murray from the University of Technology, Sydney, have also detected gambierdiscus as far south as Merimbula – 460km south of Sydney – for the first time.

“We never realised until now that they could survive in such cold conditions,” Dr Murray said.

She said it’s difficult to tell for certain whether the Merimbula microalgae – which don’t contain the ciguatoxin – had been there all along or was a recent arrival. What is known, however, is that the East Australian Current is strengthening because of global warming, bringing warmer water and sub-tropical species into previously more temperate seas.

These include Spanish mackerel, the species of fish that led to the poisoning in NSW and most if not all of the 55 cases in Queensland so far this year – almost triple the tally of last year.

Dr Murray says the Sydney Fish Market is among the most active markets in Australia in imposing limits on the sale of certain fish to reduce the likelihood of poisoning.

Since 1999, it has barred the sale of Spanish mackerel larger than 10 kilograms whole, or eight kilograms gutted – limits often not known to many recreational fishers.

Food Authority NSW says other species that have caused ciguatera poisoning in humans include coral trout, red emperor, wrasse, reef cod, sturgeon fish, trevally, queenfish, chinaman, red bass, groper, barracouta and kingfish.

“The higher risk tends to be the predatory species that eat herbivorous fish,” said Dr Christopher Bolsh, senior lecturer at the University of Tasmania’s Institute for Marine and Antarctic Studies. “Ciguatera is probably the most serious human seafood poisoning issue.”

“We do need a wake-up call,” Dr Bolsh said. “It’s difficult to get recognised and worked out before it becomes a serious problem.”

It’s already a serious issue in the tropical Pacific, including the Cook Islands, where Dr Murray has worked. There, as many as 70 per cent of the population has been afflicted as the microalgae spreads, with some local communities giving up spear fishing and one of their main sources of exercise and protein.

“It’s increasing its abundance,” Dr Murray said. “It’s gone up 60 per cent in the past 15 years.”

Again, climate change appears to be playing a role. Microalgae thrive as waters warm but also as corals die off – an outcome triggered by more intense storms but also from coral bleaching, Dr Murray said.