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How climate change poisons our food
There's no cure for a mysterious type of food poisoning known as ciguatera. But as our planet warms, it's likely to become much more common.
One thing I've come to love about travelling around Mexico is that you're rarely far from a toilet. Yes, it will cost you five pesos (£0.20), but it's a small price to pay for a few folded squares of toilet paper, a clean seat and peace of mind (and bottom). But what I didn't know as I explored Oaxaca last May, spending a few pesos to slowly, sweatily tour the bathrooms of the city's cathedral, a few ceramics shops and the sprawling Mercado de Abastos, was that I didn't have a typical, run-of-the-mill case of food poisoning. I had what I now lovingly call "my freaky fish poisoning".
Some 12 hours after that first wave of nausea, as I was sitting alone in my holiday rental, the numbness in my fingers and toes crawled up to my wrists and ankles. The odd tingling felt as though I'd woken up in an odd position and my hands and feet were asleep – only instead of gradually improving and returning to normal, the numbness just steadily continued. It suddenly occurred to me that if it persisted, I might struggle to call for help by the time I needed it. So I did the only rational thing I could think of at the time: I walked down the street for ice cream.
The author first became violently ill while exploring Oaxaca's sprawling Mercado de Abastos (Credit: Orbon Alija/Getty Images)
The culprit, I would eventually find out, was ciguatera: a strange, specific form of food poisoning stemming from a toxin in certain types of fish. It is acutely misirable for 12 hours and has effects that often last months and sometimes years. There's no way to screen fish for it and no known cure, and it's likely to become far more common as climate change warms our oceans and causes more storms, and more widespread as more fish is exported around the world.
There's no way to screen fish for it and no known cure, and it's likely to become far more common as climate change warms our oceans
Given that I wasn't exactly eating a ton of seafood as I chowed through the inland city of Oaxaca's corn-based specialties – tlayudas, tetelas and tamales– I can take an educated guess and blame the illness on the ceviche I ordered from a high-end restaurant in the city centre. But, as in all food poisoning cases, without lab testing that specific dish, there's no way to know for sure. And as I would soon learn, being aware of the danger would have been unlikely to stop me getting it.
As someone who views food as an accessible entry point to a local culture, I consider eating anything and everything I encounter to be an informative and delightful way to learn about a place and its people. I've never exercised caution around what I eat while I travel – beyond smartly skipping an oddly grey hamburger on a regional South-East Asian airline that felled my husband for a few days. This has, of course, bitten me once or twice, usually resulting in a rough night, though nothing serious. But standing in El Llano Park that afternoon, licking my scoop of zapote negro (a persimmon-like black fruit) ice cream, I had no idea that months later I would still be feeling the repercussions: rolling around in my bed in Seattle, unable to sleep because of the numbness and tingling in my fingers.
Food can be a great entry point to learn about a local culture while travelling (Credit: Ali Çobanoğlu/Getty Images)
According to Dr Mindy Richlen, a research specialist at Woods Hole Oceanographic Institution who studies harmful algal blooms, ciguatera poisoning comes from eating fish contaminated with ciguatoxins, which come from a tropical dinoflagellate (tiny single-cell organism) that lives on microalgae growing, mostly, on dead coral. More plainly: dead reefs breed infected fish food, and humans get sick when they eat the fish that eat it. While ciguatera initially presents itself as standard food poisoning, it eventually morphs into numbness in the fingers and toes that recurs for months or even years, and sometimes causes a switching of hot and cold sensations (a side effect I thankfully lucked out of, but which leads people to think their cold soda is burning them or causes them to drink far-too-hot coffee).
The Centers for Disease Control and Prevention (CDC) states that up to 50,000 cases of ciguatera poisoning are reported annually worldwide, but nobody really knows how common it is
Despite rising ocean temperatures and related weather phenomena bringing ciguatera to the headlines, the toxin is extremely common and has been around for a long time. Back in the 4th Century BC, Alexander the Great supposedly forbade his soldiers to eat fish because of an illness thought to be ciguatera. It was fascinating to read the 18th-Century description by one of Captain James Cook's crewmates of what was likely ciguatera poisoning as they explored the South Pacific aboard the HMS Revolution and compare it to my own. "The fingers, legs and toes, felt often as if benumbed: nay the whole limbs became in some measure paralytic." The following decade, Vice-Admiral William Bligh may have contracted ciguatera after eating mahi mahi while he and his loyalists were stranded on an island following the storied Mutiny on the Bounty.
The illness is likely to become much more common as climate change destroys coral reefs (Credit: Rainer von Brandis/Getty Images)
The Centers for Disease Control and Prevention (CDC) states that up to 50,000 cases of ciguatera poisoning are reported annually worldwide, but nobody really knows how common it is, because, like me, many people don't realise what they have until long after they've consumed the fish. Plus, the only way to truly ascertain if the fish is contaminated is by testing it in a lab. Ciguatera has been blamed for a tiny number of deaths over the years – mostly due to complications stemming from the effects of the toxin on the neurological and digestive system – but it's rarely fatal.
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"Ciguatera is often overlooked," said Richlen. "If you go in the literature, there will be these wild estimates like '50 to 500,000 people are poisoned per year,'" because it's hard to really know who has it. Fish carrying the ciguatoxin don't look any different; there's no feasible way to test fish for it; and neither cooking nor freezing the fish kills it. There's also no known cure or antidote for ciguatera poisoning.
The day after my poisoning, numbness lingered in my hands and feet as I boarded a plane to Mexico City. But it soon faded and I didn't think about it again until a few weeks later. Lying in bed after a lavish sushi meal on the Baja Peninsula, I felt just like that night in Oaxaca, minus the digestive issues. So, like any good millennial, I consulted Dr Google to see what could be going on and finally landed on information about an illness that matched my symptoms. The timing of my initial digestive symptoms in Oaxaca and the related numbness tracked perfectly, but the clinching factor in my self-diagnosis was when I got to the segment about long-term effects.
Fish carrying ciguatera don't look any different; there's no feasible way to test for it; and neither cooking nor freezing the fish kills it (Credit: JHLee/Getty Images)
The online info noted that recurrent episodes of the neurological effects of ciguatera – such as numbness – are thought to be tied to eating certain foods, including one of my personal sushi favourites, red snapper. A fun piece of the puzzle is that nobody really knows which foods, though fish is a likely one, particularly reef fish. Various sources list peanuts, chicken, pork, alcohol, caffeine and even exercise as likely triggers. Oddly, in the months since I first contracted ciguatera, I've found Sichuan food to be a particular one for me, though I have no idea what specific ingredient that might be related to.
Most diagnoses of ciguatera are based on the type of fish the person eats and the region where the fish was caught. It's particularly common in the tropical Caribbean, Indian and Pacific oceans – the kind of sunshine-filled, beach-boasting places that pepper travellers' dreams – and from eating reef fish like snappers and groupers. But after consulting my photo of the menu at the high-end Oaxaca restaurant where I think I contracted ciguatera, it only revealed that I ordered the "fish of the day", served as a ceviche and marinated in "recado negro" (black chilli sauce), served with cucumbers, red onions and habanero peppers.
Ciguatera is particularly common in tropical climates where coral reefs are prevalent (Credit: SHansche/Getty Images)
While the latitudes of Oaxaca fall within the CDC's guidelines of where most poisonings take place (between 35°S and 35°N), no instances have been officially reported here. Given the unknown origin of the fish I ate and the clarity of my symptoms, Richlen agreed that it was likely ciguatera. But since there's nothing that can be done about it once you have it, an official diagnosis (were there a way to test for it) would be pretty useless.
The areas where people are contracting ciguatera are changing due to another reason: climate change
To Richlen, the lack of information about the fish that sickened me highlights one of the biggest issues with ciguatera. "With the increased export of fish around the world, you're going to have people [contracting it] in [landlocked] places like the [American] Midwest," she said. Richlen cites a 2004 outbreak at a Hong Kong fish market from bringing in fish from the South Pacific. According to the United Nations, from 1976 to 2016, the amount of seafood exported around the world for human consumption grew by 514%, and it is projected to grow another 24% by 2030. Another researcher working on ciguatera at Florida Gulf Coast University, Dr Mike Parsons, mentions that he fielded a call from a lawyer whose clients contracted ciguatera from eating barracuda in New York City.
Parsons also believes that the areas where people are contracting ciguatera are changing due to another reason: climate change. "I think people will be catching toxic fish in areas [where] ciguatera was not prevalent before." Richlen and Parsons explained that warming ocean temperatures have changed the range of where ciguatera grows: the water has become too warm for the toxic dinoflagellate to grow in places where it once did, while it now flourishes farther north where it used to be too cold. In places like the Gulf of Mexico, Parsons explained, the tropical and subtropical dinoflagellate used to die back in winter, but now stays and grows year-round.
Ciguatera is contracted when people eat fish that have fed on algae growing on damaged coral (Credit: vojce/Getty Images)
Another element of prime ciguatera growth, though, is Parsons' specific area of expertise: the relationship between the prevalence of ciguatoxins (and the marine life carrying it) and damaged coral reefs. Whether due to bleaching, increased hurricane activity or reef degradation from human activities, he said, "I would expect to see ciguatera flaring up as reef health declines." Currently, he's comparing the distribution of the toxic dinoflagellates in areas of the Bahamas that were hit and spared by Hurricane Dorian in August.
Despite the ongoing study of ciguatoxins, there's still not a ton of reliable information about why dead reefs breed them. According to Richlen, dinoflagellates live on a type of algae that thrives in dead reefs, and this algae is the preferred food for many reef fish. The fish think they wandered into the marine version of a candy shop, goble up the toxin-laced algae and spike the likelihood of humans contracting ciguatera. In the last 30 years, 50% of all of the world's corals have died due in large part to climage change, and some predictions say 90% may die in the next century.
Experts recommend avoiding reef fish, like snapper, to reduce the risk of ciguatera (Credit: bhofack2/Getty Images)
As someone who travels around many of the areas where ciguatera is endemic, I asked Richlen and Parsons if there's anything they would avoid when travelling help prevent contracting ciguatera. Both immediately cited barracuda, a prime ciguatera culprit because it eats the smaller, contaminated reef fish. But Richlen recommended not eating reef fish, in general, like snapper and grouper. "Reefs are under so much pressure from a variety of sources, including overfishing. I probably would just skip it for multiple reasons," she said. Parsons said that he knows of resorts on St Thomas and St Croix, among other islands, that go so far as to import their fish. "They won't use the local fish because they don't trust it enough, they don't want their clientele to get sick."
He also noted out that bigger fish are more likely to accumulate the toxins that carry the disease, so smaller fish are likely to be safer to eat. "The important thing is to know what fish you're eating and where it's caught" and to know what fish in the area might carry it, he said. Richlen sent me a few posters from around the world that warn people about problematic fish, such as giant sweetlips in Fiji or yellow jack in Guadeloupe, and Parsons suggested talking to local fishermen about which fish are safe as they will know best.
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Nearly eight months later, I still get recurrences. I no longer worry about my hands becoming permanently paralysed or that it might be fatal, as I did on the first day. Instead, I laugh about my freaky fish poisoning and marvel at how little we know, as eaters, about what we consume, particularly while travelling. Even armed with my newfound knowledge about ciguatera, I realise that still none of this would have helped me. I didn't know what fish I was eating. I didn't know where it came from. All I knew was that it was good, and I know now that I'd probably do it again. Of course, since getting ciguatera once makes you more susceptible to the toxin, I probably will get it again.
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