The bacterium Vibrio vulnificus is both an under-reported problem and a bug that is often sensationalized - as A Flesh Eating Parasite! – in the media. While that isn’t really the truth and it is quite rare, it’s still a pretty nasty customer, with some types of infection having fatality rates of up to 50%.
What exactly is it and where would one find it?
V. vulnificus is one species of the Vibrio type of bacteria. There are hundreds of Vibrio species, but only 11 are known to cause illness is humans, one of the others being the charming one responsible for cholera. Like all Vibrio species, V. vulnificus is a gram negative, rod shaped bacterium, but it also has one other special characteristic – it is a halophilic organism - which basically means it is ‘salt-loving’. Due to this, it is found naturally in oceans, marine estuaries, salt marshes and other areas of brackish water.
It also likes a warm environment, thus it is usually only found in shallow coastal areas where the average yearly temperature does not become too cold. It is most common around the coast of America – particularly in the Florida and Gulf of Mexico area – but it can also be found on the Australian and eastern South American coast as well as in the marine areas of Southern Africa. There have been isolated cases in other areas such as the Mediterranean and Asia, but it is very rare there.
It was first documented as late as 1976, and the first reported case of human infection was in 1979. The fact that is a naturally occurring bacterium that does not necessarily reflect pollution or unsanitary conditions means it is very pervasive and is becoming a growing problem is places such as the US where it is now the leading cause of Vibrio related deaths.
What type of illness does it cause and how would one catch it?
The main type of illness associated with V. vulnificus is a form of gastroenteritis that arises from eating seafood contaminated with the bacteria. Oysters and shellfish are the main culprits as they are often eaten raw or very lightly cooked which means that the bacteria is not killed before consumption. A person who has eaten such food may begin to experience symptoms such as vomiting, diarrhoea, and abdominal pain within 16 hours from the meal.
The real danger here is for people with liver damage, such as cirrhosis or a history of heavy drinking and those with a suppressed immune system, for example those with AIDS. In people with either of these conditions, V. vulnificus usually enters the blood stream and causes primary septicaemia and only needs a dose of about 100 organisms to do so. This results in sceptic shock and the appearance of bullous skin lesions which is rapidly followed by death if not treated in time – in these cases the fatality rate is about 50%.
The second type of infection results from an open wound coming into contact with seawater containing the bacteria. The wound only has to be as small as a tiny skin deep cut to let in enough bacteria to cause illness. In this case, the first symptom would be cellulitis at the site of the wound, this includes red, inflamed skin and itching and breaking of the skin surface. Once the bacteria are firmly established under the skin surface it then enters the bloodstream, again resulting in septicaemia. However unlike with the ingested form, this happens to both healthy people as well as those with the medical conditions mentioned above.
At the site of the wound necrotizing fasciitis often sets in – this is where the bug has gotten its terrifying flesh-eating reputation from. This condition causes rapid destruction of the skin and flesh and can even spread to the underlying muscle. It spreads incredibly fast and one wound site can quickly spread the disease to many areas of the body. If left untreated, death usually results in 12 to 24 hours and even with treatment it is fatal about 70% of the time.
Prevention is better than cure
Because V. vulnificus only thrives in very warm water, infections are usually seasonal, with the highest number occurring in the warmer months, usually June to October in the Gulf area. Knowing when it is most prominent helps in its prevention – for example, in many coastal states the collection of oysters and shellfish is prohibited during these warm months as the animals are almost guaranteed to be infected.
Obviously, the best way to prevent food borne transmission of the illness would be not to eat raw seafood that contained the bacterium. However, since it does not change the smell, taste or appearance of the food, detecting it can be difficult. Also, a study done by the CDC showed that 85% of cases came from food eaten at a restaurant which complied with the restrictions on harvesting, and none came from self harvests, which shows that even the best efforts to only catch at safe times and in safe places is not enough.
Importantly, the bacteria can very easily be killed by cooking, however as seafood is usually supposed to be eaten in a raw or near-raw state this is not always desirable, but for those with liver or immune conditions it is the advised way.
Because the gastro caused by V. vulnificus is self-limiting and usually requires no treatment, cases of it are very underreported, because people get better after a few days and think nothing of it except an unlucky brush with food poisoning. Over the past 20 years, CDC records only show about 400 reported cases - which are diagnosed with a stool culture – however it is suspected that the real number is much much higher.
In cases of direct contact with seawater, again it is fairly obvious to note that one should not go swimming in such areas with an open wound. However as the wound does not need to be big and small cuts often go unnoticed this is no guarantee. Many of the reported cases are of fishermen who perhaps had a small cut on their hand and did no more than kneel down and wash their hands in the sea.
It is recommended that if one has been swimming in such an area and a cut becomes red or itchy soon after, one should report to a doctor immediately. The bacteria can easily be recognized by doing a blood or wound culture and if diagnosed early enough can be easily treated with antibiotics. The Florida Department of Health and Rehabilitative Services records that between 1981 and 1992 125 people with this type of infection were treated, this number has risen slightly over the past few years.
If the disease has progressed beyond this stage, hospitalization is required. The patient will be given antibiotics as well as intravenous liquids to try and counter fluid loss. Surgery will be performed to remove areas of infected skin. All lesions as well as their underlying flesh will be cut out, however as the bacteria spread so rapidly, amputations are often necessary to stop its progress. Those who were previously healthy have a chance of full recovery if caught in time, but those with liver damage are up to 200 times more likely to die.
So, on a final note, if you don’t really want to get it, here is a prevention summary:
- If you are in one of the high risk categories (liver damage, HIV/AIDS, diabetic, hemochromatosis, achlorohydria) do not eat raw shellfish or oysters!
- At Restaurants: Order oysters fully cooked.
- Cooking at Home:
- In the Shell: Cook live oysters in boiling water for three to five minutes after shells open. Use small pots to boil or steam oysters. Do not cook too many oysters in the same pot, because the ones in the middle may not get fully cooked. Discard any oysters that do not open during cooking. Steam live oysters for four to nine minutes in a steamer that’s already steaming.
- Shucked: Boil or simmer for at least three minutes or until edges curl. Fry in oil for at least three minutes at 375 °F. Broil 3 inches from heat for three minutes. Bake (as in Oysters Rockefeller) for 10 minutes at 450 °F.
- Avoid exposure of recent or healing wounds, cuts, punctures, or burns to warm seawater. When swimming or wading, temporarily cover wounds with watertight wrap
- Avoid cross-contamination of previously cooked shellfish with raw shellfish.
- Wear protective clothing (e.g., gloves) when handling raw shellfish.
- Vibrio Vulnificus Infections by Dr. Cris Jager - http://www.emedicine.com/derm/topic847.htm
- Toward Safer Oysters: A GENE TEST FOR A TROUBLED INDUSTRY by Frank Stephenson - http://mailer.fsu.edu/~research/RinR/oysters.html#vv
- FDA/CFSAN Bad Bug Book Vibrio vulnificus - http://vm.cfsan.fda.gov/~mow/chap10.html
- CDC - http://www.cdc.gov/ncidod/dbmd/diseaseinfo/vibriovulnificus.htm