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Ciguatera Fish Poisoning: Food Poisoning That Can Last for Years

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You wake up one morning with stomach pain and chills and assume you have food poisoning from some bad fish. However, over the next few days your symptoms take a turn for the weird. You are still nauseous, but now hot showers feel freezing cold, and your teeth feel loose. You finally drag yourself to the doctor, and after a battery of tests you are diagnosed with ciguatera fish poisoning (CFP). Wait, what?

CFP is not well known, yet is the most common seafood-toxin illness in the world, with 50,000 reported cases annually, and many more that go unreported. It can cause a wide range of symptoms including nausea, vomiting, respiratory paralysis, and weird neurological confusion like perceiving hot things as cold.

“The illness that it causes is really debilitating, and it’s debilitating for weeks and months right after the food they had, and in quite a few cases, for years after the poisoning,” explains Dr. Donald Anderson, a senior researcher at the Woods Hole Oceanographic Institute. Currently there is no known treatment, and thanks to rising ocean temperatures, CFP may soon become more common in the U.S.

CFP is caused by ciguatoxin, which is produced by a group of algae species called Gambierdiscus. These algae species settle on seaweed and coral, where they are incidentally ingested by grazing herbivorous fish species. Herbivorous fish species are then consumed by predatory fish like red snapper, grouper, or sea bass, which in turn are consumed by humans. Each move up the food chain magnifies the ciguatoxin until it reaches dangerously high concentrations.

Previously, toxic Gambierdiscus species were mostly limited to tropical and sub-tropical regions like the Caribbean, with occasional cases in Florida and Texas. However, as ocean temperatures continue to rise, that may soon change. “It’s very common these days that organisms of many different types in the ocean are shifting their ranges towards the north as waters warm,” says Dr. Anderson. “We are in the path of that northward movement [for Gambierdiscus species].” A recent NOAA study suggests that rising ocean temperatures will cause certain Gambierdiscus species to expand their ranges to the northern Gulf of Mexico and the U.S. southeast Atlantic coast. Increased incidence of CFP is likely to follow.

Ciguatoxins do not affect the fish that ingest them, they cannot be detected, and they aren’t destroyed by freezing or cooking. When it comes to avoiding CFP, the best approach is to not eat predatory fish species. People who consume these fish species rely on local knowledge to keep them safe. “The locals know all about it, and they either avoid eating fish from one side of an island that they know is dangerous, or they know certain fish to avoid,” explains Dr. Anderson. However, as the ranges of these toxic algae species shift in response to rising ocean temperatures, local knowledge may no longer be enough.

There are five toxic Gambierdiscus species that differ in their temperature range and toxicity, yet are virtually indistinguishable under a microscope. Dr. Anderson and his lab are currently developing ways to figure out the presence and abundance of Gambierdiscus species in a particular area.

One promising technique involves designing DNA probes, short chunks of DNA known as tags. Each species would have a unique DNA tag that attaches onto a complementary section of its RNA. If you add the tags to a mix of species in a water sample, you can use a microscope to count the tags that attach, and determine what species are present, and in what proportion. This approach would provide a way of quickly determining the threat of CFP at a location, which will become increasingly important as CFP creeps steadily into the U.S.

 

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