Modes of Vibrio vulnificus Infection
Vibrio vulnificus Bacteria
Vibrio vulnificus is a gram- negative, motile, halophilic, straight or curved rod-shaped bacterium. It is a natural inhabitant of marine environments, especially areas with low salinity (0.5 to 2.0% sodium chloride) i.e., near shorelines and in estuaries where freshwater from rivers mixes with saltwater from oceans. The presence of the bacteria is neither a result of chemical or biological pollution.
V. vulnificus bacteria prefer a warm environment and reproduce rapidly when water temperatures are 86°F to 95°F and salinity levels are approximately 0.5% sodium chloride. During warm weather months in the Gulf of Mexico, levels of bacteria can reach 100 to 1,000 cells/ml seawater, 10,000 cells/gm sediment, and 100,000 cells/gm oyster meat (1). In the United States, the highest seawater concentrations of the bacteria are found in the Gulf of Mexico from April to October. The bacteria are present, but at much lower levels, in other U.S. coastal waters and have also been detected in seawater and shellfish in other countries (2, 3, 4, 5, 6).
More than 100 different strains of V. vulnificus have been isolated from oyster meat (1). However, not all strains are pathogenic. Once pathogenic V. vulnificus bacteria are ingested, they use hair-like structures called pili to attach to mucosa epithelium cells and invade the body. One trait that affects virulence is the presence of a polysaccharide capsule, which may enable the bacteria to evade host defenses (7). When isolated using laboratory techniques, these V. vulnificus bacteria appear as opaque colonies on agar (1).
In addition to entering the body through the gastrointestinal tract, V. vulnificus bacteria may also gain access through open wounds or sores exposed to ocean water containing the bacteria. Once inside the body, V. vulnificus bacteria reproduce rapidly. The bacteria secrete proteases, lipases and other enzymes that lyse host cells, causing extensive necrosis in tissues around wounds and in the lower extremities through fluid leakage through capillaries. High-risk patients who develop septicemia from a V. vulnificus infection may die within 24 hours of ingesting raw shellfish.
The infectious dose of V. vulnificus bacteria for healthy people is unknown. However, less than 100 total organisms can cause illness in high-risk patients. Other less virulent marine-related pathogenic species from the Vibrio family include V. parahaemolyticus, V. cholerae, V. alginolyticus, V. fluvialis, V. hollisae, and V. metschinikovii.
Infections from Raw Shellfish Consumption
Approximately 40% of all V. vulnificus cases reported in the U.S. from 1998 to 2004 were caused by consumption of raw or undercooked molluscan shellfish (oysters, clams, or mussels). During this seven-year period, the number of shellfish cases reported each year ranged from 28 to 41 (refer to bar graph). A statistical analysis of shellfish cases from 1993 to 2003 showed that 94% of cases were associated with raw oysters, 4% with under-cooked oysters, and 2% with hard clams or other shellfish (8).
U.S. V. vulnificus Cases by Year 1998 - 2004
Healthy patients usually do not contract V. vulnificus infections from eating raw shellfish. However, high-risk patients are much more susceptible to V. vulnificus infection and are likely to develop serious symptoms that can lead to septicemia and/or death.
Wounds infected with V. vulnificus bacteria account for approximately 60% of all U.S. cases. V. vulnificus infections may occur in healthy and high-risk patients when pre-existing open wounds or sores are exposed to seawater containing the bacteria or when an individual receives a wound while engaging in a marine-related activity. Coastal recreational activities that may produce wound infections include swimming, wading, boating, fishing, and shellfish harvesting/shucking. Occupational marine or food-related activities that may cause wound infection include harvesting or handling Gulf of Mexico seafood, shucking Gulf oysters, and picking crab meat from Gulf coast crabs. In addition, cases of wound infections have been reported from marine-related activities in the mid and south Atlantic coastal regions of the U.S.
Contact with flood waters caused by hurricanes in the Gulf of Mexico has also resulted in V. vulnificus wound infections. The Centers for Disease Control and Prevention (CDC) reported 14 wound-associated cases (three fatal) among Mississippi and Louisiana residents exposed to floodwaters after Hurricane Katrina made landfall on August 29, 2005 (9).
During September 2005 the CDC issued a Health Advisory on V. vulnificus cases in Hurricane Katrina evacuees10 and updated information on emergency wound management with special consideration to flood conditions11.
Photo Credit: Food and Drug Administration
The severity of wound infections depends on the patient's health status. Healthy and high-risk patients may develop cellulitis. However, in high-risk patients, wound infection may also result in septicemia and/or death.
Unusual Modes of Infection
Other, uncommon modes of V. vulnificus infection have been reported. One unusual case involved necrotizing cellulitis that developed after an Israeli traditional folk healer treated a chronic leg ulcer by spraying it with fresh fish blood12. Another atypical case involved a man who was struck by lightning while windsurfing and was found without a pulse in the ocean13. Although the exact entry of V. vulnificus bacteria was never determined with certainty, the authors suggested that ingestion of seawater or small, incidental, cutaneous injuries were possible modes of infection. Finally, corneal ulcers resulting from ocular contamination with V. vulnificus were documented in a case study of a man who was employed as an oyster shucker in a seafood processing plant13. Oyster shell fragments that had lodged in his eyes were the cause of the infection.
- Tamplin, M., R. Hammond, P. Gulig, and R. Baker. 2001. Vibrio vulnificus, a hidden risk in raw oysters (video). A clinician's guide to V. vulnificus infection and treatment. (Request via Interstate Shellfish Sanitation Conference order form.)*
- Arias, C.R., M.C. Macian, R. Aznar, E. Garay, and M.J. Pujalte. 1999. Low incidence of Vibrio vulnificus among Vibrio isolates from sea water and shellfish of the western Mediterranean coast. Journal of Applied Microbiology. 86:125-134.>
- Cavallo, R.A., and L. Stabili. 2002. Presence of vibrios in seawater and Mytilus galloprovincialis (Lam.) from the Mar Piccolo of Taranto (Ionian Sea). Water Research. 36:3719-3726.
- Hervio-Heath, D., R.R. Colwell, A. Derrien, A. Robert-Pillot, J.M. Fournier, and M. Pommepuy. 2002. Occurrence of pathogenic vibrios in coastal areas of France. Journal of Applied Microbiology. 92:1123-1135.
- Jaksic, S., S. Uhitil, T. Petrak, D. Bazulic, and L. Gumhalter Karolyi. 2002. Occurrence of Vibrio spp. in sea fish, shrimps and bivalve molluscs harvested from Adriatic Sea. Food Control. 13:491-493.
- Thampuran, N., P.K. Surendran. 1998. Occurrence and distribution of Vibrio vulnificus in tropical fish and shellfish from Cochin (India). Letters in Applied Microbiology 26(2):110-112.
- Yoshida, S, M. Ogawa, Y. Mizuguchi. 1985. Relation of capsular materials and colony opacity to virulence of Vibrio vulnificus. Infectious Immunity. 47:446-451.
- Bashin, M. 2004. Vibrio vulnificus Case Analysis 1993 - 2003 (unpublished report). Interstate Shellfish Sanitation Conference.
- Vibrio illnesses after Hurricane Katrina -- multiple states, August -- September 2005 [Internet]. Atlanta (GA): Centers for Disease Control and Prevention, MMWR 54 (Dispatch); 1-4 [2005 September 14; cited 2005 October 26]. Available from: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm54d914a1.htm
- Cases of Vibrio vulnificus identified among Hurricane Katrina evacuees [Internet]. Atlanta (GA): Centers for Disease Control & Prevention, Health Advisory no. 233. [2005 September 7; cited 2005 September 10]. Available from: http://www2a.cdc.gov/HAN/ArchiveSys/ViewMsgV.asp?AlertNum=00233
- Emergency wound management for healthcare professionals [Internet].
- Tal, S, V. Guller, O. Zimhony, S. Levi, M. Greenshpun, A. Gurevich. 2004. A "fishy remedy": an unusual transmission of Vibrio vulnificus infection. Southern Medical Journal 97(2): 205-207.
- Ulusarac, O and E. Carter. 2004. Varied clinical presentations of Vibrio vulnificus infections: a report of four unusual cases and review of the literature. Southern Medical Journal 97(2): 163-168.