Ciguatera, human poisoning resulting from eating some exotic fish varieties, is increasing all along the coastal regions in the world, reports say. Upto 50,000 people worldwide fall victims to it every year, it is estimated.
Scientists say the risks are getting worse, because of the damage that pollution and global warming are inflicting on the coral reefs where many fish species feed.
Dozens of popular fish types, including grouper and barracuda, live near reefs. They accumulate the toxic chemical in their bodies from eating smaller fish that graze on the poisonous algae. When oceans are warmed by the greenhouse effect and fouled by toxic runoff, coral reefs are damaged and poisonous algae thrives.
Ciguatera has long been known in the South Pacific, the Caribbean and warmer areas of the Indian Ocean. Some South Pacific islanders use dogs to test fish before they eat.
But in the past decade, it has spread through Asia, Europe and the United States, where more restaurants are serving reef fish, prized for their fresh taste.
In the United States, ciguatera poisonings are most frequent in Florida, Texas and Hawaii, which has seen a fivefold increase since the 1970s to more than 250 a year.
Hong Kong, which imports much of its seafood, went from fewer than 10 cases annually in the 1980s to a few hundred now.
Initial signs of poisoning occur within six hours after consumption of toxic fish and include numbness and tingling, which may spread to the extremities, nausea, vomiting, and diarrhea.
Headache, acute sensitivity to temperature extremes, vertigo, and muscular weakness apart from cardiovascular complications also could follow.
This, however, is known to be self-limiting, symptoms subsiding after a few weeks. But in a few cases, they could persist, rarely resulting in death too.
"Worldwide, we have a much bigger problem with toxins from algae in seafood than we had 20 or 30 years ago," said Donald M. Anderson, director of the Coastal Ocean Institute at the Woods Hole Oceanographic Institution in Massachusetts.
"We have more toxins, more species of algae producing the toxins and more areas affected around the world," he said.
Although risk of ciguatera has soared recently, the phenomenon is ancient. Fish poisoning shows up in Homer's Odyssey. Alexander the Great forbade his armies to eat fish for fear of being stricken.
Capt. James Cook and his crew probably suffered ciguatera poisoning in 1774 after eating fish near Vanuatu in the South Pacific.
Cook has recorded that they "were seized with an extraordinary weakness in all our limbs attended with a numbness or sensation like ... that ... caused by exposing one's hands or feet to a fire after having been pinched much by frost."