About 12 species of Vibrio bacteria cause sickness in humans, the CDC says
Warmer waters may be leading to an increase in infections, experts say
There have been a number of recent reports warning the public of the dangers of Vibrio bacteria from eating certain foods or swimming at the beach. An infection can result in gastrointestinal issues, the loss of limbs and even death. But what are these bacteria?
“These are interesting organisms and range in scale from massive global epidemics – cholera – to infrequent but lethal infections – Vibrio vulnificus,” said Rita Colwell, a professor in the University of Maryland’s Department of Cell Biology & Molecular Genetics and former director of the National Science Foundation.
There are about 12 species of Vibrio bacteria that cause sickness in humans, known as vibriosis, according to the US Centers for Disease Control and Prevention. About 80% of infections happen between May and October, when waters are warmer, and usually after a person eats infected shellfish.
Vibrio parahaemolyticus, Vibrio vulnificus and Vibrio alginolyticus are the three most common species that cause illness in the United States, reports the CDC. Another notable strain, Vibrio cholerae, is not widespread in the US.
Symptoms of Vibrio infection include watery diarrhea, abdominal cramping, nausea, vomiting, fever and chills. Treatment is not always needed, and severe illness is rare, but doctors prescribe antibiotics in more persistent cases, the agency says.
Vibrio parahaemolyticus is the most commonly reported species, responsible for 45,000 of the 80,000 Vibrio illnesses per year in the United States, the CDC says.
“It’s associated with ingesting seafood that has not been properly cooked, or properly stored and then not properly cooked,” Colwell said. “And also by taking oysters or seafood from contaminated areas, which sometimes people do, especially in Florida or in the Gulf, where there’s a sign that says ‘fishing prohibited’ but the oysters grow big and fat. And they look good, so they eat them.”
Vibrio alginolyticus typically causes ear infections and swimmer’s ear, said James D. Oliver, a professor of microbiology in the Department of Biological Sciences at the University of North Carolina at Charlotte.
“Personally, it’s not something I worry about at all,” said Oliver, who is also a fellow in the American Academy of Microbiology.
Vibrio vulnificus, however, is an infection to be wary of, he said.
The bacteria reside in seafood and brackish (mixed fresh and salt) water. They can cause a skin infection when open cuts and sores are exposed to tainted water. There are about 205 infections per year, the CDC says, but one in four people with this infection dies, and some must have limb amputations to stop the spread of infected tissue. Vibrio vulnificus is occasionally mislabeled as “flesh-eating” bacteria, though it actually damages the skin.
Vibrio vulnificus is very responsive to antibiotics, but the medication must be administered quickly, within a day or so, Oliver said. If there is any indication of infection like redness and swelling, a person should seek medical attention, he said.
The very young, the very old and individuals who have suppressed immune systems or high levels of iron in the body are particularly at risk, Colwell said.
“In people who’ve got liver disease – that could be hepatitis or cirrhosis or another liver disease – those are chronic damaging situations of the liver,” Oliver said. “Its cells are being destroyed, releasing iron into the bloodstream, and that released iron exceeds the capacity of your blood to sequester it away. So you in essence get free iron in the blood, and that allows these bacteria to proliferate very, very rapidly.”
Paul A. Gulig, a professor in the Department of Molecular Genetics and Microbiology at the University of Florida, noted that “for the raw oysters, by far most of the people who get seriously ill from that have the predisposing conditions. But … you can be otherwise healthy and get the wound infection because you’re introducing the bacteria right into your tissue.”
The CDC’s recommendations for lowering the risk of any form of Vibrio infection include not eating raw or undercooked shellfish, particularly oysters, and avoiding swimming in brackish and estuarial water if you have any broken skin (or at least wearing a waterproof bandage).
Though Vibrio cholerae is not a major health concern in the United States, there are 1.3 million to 4 million cases of the disease cholera and up to 143,000 deaths from it annually around the world, the World Health Organization says.
“If people travel to places where it’s endemic, they can pick it up and bring it back,” Gulig said. “But it’s not a disease that people pick up when they’re in the United States. We don’t have it in our water and our food. It’s mainly a disease of developing countries from poor sanitation and poor water hydration.”
Most people who are infected have no symptoms or mild to moderate ones. Cholera also causes a watery diarrhea that can be treated by replacing fluid loss with water and electrolytes and occasionally antibiotics. If left untreated, severe dehydration can lead to death within hours.
“For cholera, I would say people going to endemic areas, traveling overseas, they should look and see what the recommendations from the CDC is on vaccination, because there are new vaccines,” Gulig said.
Changes in recent years in Vibrio testing, moving from bacterial cultures to newer tests that may offer less information about the specific strain of Vibrio causing an infection, have made it difficult for the CDC to compare changes from year to year, said Dr. Karen Wong, a medical officer at the agency.
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“But we have noticed that over the years, we’ve seen Vibrio infections in places that we haven’t seen them before,” Wong said, pointing to infections in more northern areas of the country.
Some experts argue that warmer climates explain the increase in infections, calling it the microbial equivalent of a canary in a coal mine.
“With warmer temps, the Vibrios proliferate,” Colwell said. “They become more numerous, and they outgrow their competitors which at lower temperatures would keep them in check.”