You’ve probably seen headlines like this before (“Raw oysters linked to two deaths”): This isn’t the first time doctors have warned people against eating raw oysters. Oysters, like mussels, scallops, sponges, krill, baleen whales and others, are known as “filter feeders.” They feed by eating plankton and extracting nutrients from the water, and they’re very good at it. Bivalves (the species to which oysters belong) are high in protein and have been a staple of our diet for the past 165,000 years. The problem comes when our planet’s climate changes and the habits and systems that work in harmony with each other become deadly.

As filter feeders, oysters are the sponge of the ocean. Eating them raw means spinning the wheel of fortune for ocean diseases that you could potentially catch with your next bite. A recent study in Nature found that cases of Vibrio vulnificus, a type of deadly bacteria found in oysters, have increased eightfold in the eastern U.S. since 1988 due to warming oceans, and the affected areas are expanding rapidly. The same study estimates that Vibrio cases will double between 2041 and 2060 at the rate our planet is warming. According to NASA, Vibrio bacteria thrive in warmer oceans, and with a warming planet, you can expect oysters to become more dangerous to eat, especially in warmer seasons.

According to the Centers for Disease Control and Prevention (CDC), about 80,000 people are infected with vibriosis, the disease caused by the Vibrio bacteria, and 100 people die from it each year in the U.S. (including from contracting open wounds in the ocean and other means), making it the leading cause of seafood-related death. The FDA reports that infection with one type of Vibrio, Vibrio vulnificus, has a mortality rate of up to 50% in people at high risk. (For reference, estimated COVID mortality rates worldwide have been as low as 5%).

An oyster that contains Vibrio bacteria will not look, smell or taste any different. If you eat one, you may experience mild illness including diarrhea and vomiting. In rare cases, you may become very ill and possibly die from bloodstream infections, severe skin blistering or limb amputation due to Vibrio vulnificus, the CDC says.