Vibrio parahaemolyticus

Vibrio parahaemolyticus is a curved, rod-shaped, Gram-negative bacterium found in brackish saltwater, which, when ingested, causes gastrointestinal illness in humans. V. parahaemolyticus is oxidase positive, facultatively aerobic, and does not form spores. This species is motile, with a single, polar flagellum.

Ingestion of raw or undercooked seafood is the most common cause of the acute gastroenteritis caused by V. parahaemolyticus. Infection can also occur from fecal-oral route as well as wounds.

Clinical isolates usually possess two pathogenicity islands which are acquired via horizontal gene transfer. The functions of PAI genes have not been elucidated although the pathogenicity islands have been sequenced. Two well-characterized virulence proteins are typically found in the pathogenicity islands, the thermostable direct hemolysin gene or the tdh-related hemolysin gene.

Coastal regions experience outbreaks most often, especially during the summer and early fall when water temperatures favor higher levels of bacteria. Seafood most often implicated includes squid, mackerel, tuna, sardines, crab, shrimp, and bivalves. There is about a 24 hour incubation period followed by explosive, watery diarrhea accompanied by nausea, vomiting, abdominal cramps, and sometimes fever. Symptoms usually resolve in 72 hours but can last up to 10 days in immunocompromised individuals. Most cases of food infection are self-limiting and usually don’t need treatment. In more severe cases fluid and electrolyte replacement might be needed.