By: Sean McNulty

Summer is drawing to a close – it’s past Labor Day, you can’t wear white anymore, and the days will soon begin to get shorter. If you’re feeling peckish and looking to slurp some raw oysters on a warm late-September night, however, you should be careful – we’re still in the season for vibrio, and those oysters could give you a set of nasty flu-like symptoms.

What is Vibrio?

Vibrio is a kind of bacteria that breeds in salt water. There’s a whole genus of them, of about which twelve different kinds can make you sick. The bacteria that causes cholera is a kind of vibrio. The vibrio we’ll be discussing here, however, isn’t Vibrio cholerae – it’s Vibrio parahaemolyticus, a cousin from the same genus.

Vibrio parahaemolyticus loves warm water. Population numbers soar between May and October, when the ocean is warmest. According to an article published by Quartz, recent research in the Proceedings of the National Academy of the Sciences has linked higher populations of vibrio to climate change slowly cooking our seas.

During the high season, vibrio accumulates in delicious marine life like shrimp, crab, and oyster. Sometimes, there’s enough vibrio in these foods to make you sick. Raw oysters in particular are notorious.

What the CDC Says

The CDC offers some pithy advice on the issue of seafood preparation: “The only way to kill harmful bacteria in oysters is to cook them properly. Hot sauce and lemon juice don’t kill Vibrio bacteria. Drinking alcohol while eating oysters doesn’t kill vibrio bacteria either. Cooking oysters properly kills harmful bacteria.” If you’re eating raw oysters, in other words, you’re putting yourself at risk for a bout with vibrio.

If you swallow enough contaminated saltwater or eat shellfish that hasn’t been prepared properly, vibrio can cause an upset stomach and diarrhea. The elderly and sick are at risk of a more serious infection, where vibrio moves to the bloodstream and can progress into a life-threatening illness.

That means to be careful with vibrio if you have problems with your liver, if you’re undergoing chemo, or if you have a condition like AIDS that might compromise your immune system. Once vibrio hits the bloodstream, it can cause sepsis and other horrifying conditions. You might lose a limb, or worse – if you get to this stage and you haven’t yet, seek care from a medical professional immediately.

There’s another way for vibrio to enter the bloodstream. If you go swimming in salty or brackish water with an open wound, there’s a possibility that vibrio can slip past your body’s defenses and cause an ugly infection – sometimes bringing rashes of ugly sores that swell with pus. Because of these symptoms, vibrio has sometimes been dubbed a “flesh eating bacteria” in the press.

That epithet is a touch sensationalist. Vibrio doesn’t eat flesh in the sense that it’ll chew through your skin if you’re to come in contact with it. It has to find a way in first, which is usually through a cut, scrape, or lesion. Taking care to avoid salty water between May and October if you’ve got a cut that’s still healing is the best way to avoid infection. Additionally, you should keep an eye on the websites of local authorities (such as public health or fisheries agencies), who will inform you if there are higher levels of vibrio than normal.

Vibrio Facts

How do we know how much vibrio is in the ocean, anyways? National Geographic reported that the study we mentioned up top – the one where warmer seas were linked to higher vibrio populations – drew from a massive shellfish survey. Trawlers in the North Atlantic have been scooping up sea creatures coated in vibrio for half a century. By putting vibrio levels next to rising sea temperatures, researchers found vibrio populations increasing two or sometimes threefold as the ocean grew warmer.

More vibrio means more cases of people getting sick. In 2013, a vibrio outbreak in Atlantic seafood sickened more than a hundred people and sent six to the hospital. Another, in 2006, affected 117. Other outbreaks reported in the CDC’s journal of infectious diseases occurred in 1996 and 1998. The others of that report noted a “increasing number of infections” from Vibrio parahaemolyticus and Vibrio vulnificus, its deadly cousin.

Another report published in the Nature Climate Change journal in 2012 connected rising vibrio measurements taken in the Baltic Sea and increasing cases of vibrio infections reported in northern Europe. Peaks in sea temperature translated to corresponding spikes in vibrio populations and the numbers of people sickened.

Vibrio has also started to appear more in colder and more temperate waters, such as the oceans off of the Pacific Northwest, Chile, and Spain. According to Reuters, the authors of the Nature Climate Change report thought that these rarer high-latitude populations of vibrio were also likely linked to warming oceans. So far, little research has been done on bacteria so far from the equator.

There are more climate-change related factors complicating the situation than rising sea temperatures. As the globe gets hotter, more water will evaporate into moisture and condense in the air. That added moisture drives rainfall, making it more frequent and more intense. A good portion of that water flows through coastal estuaries, lowlands, and marshes – the environments in which Vibrio bacteria like to live.

All that freshwater lowers the salt content of these environments. That makes them more amenable to vibrio, which prefer saltwater with a lower salinity content. As the seas get warmer and the marshes get less salty, their number will likely continue to rise



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