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. Like other members of the genus Vibrio, this species is motile, with a single, polar flagellum.

Pathogenesis
While infection can occur via the fecal-oral route, ingestion of bacteria in raw or undercooked seafood, usually oysters, is the predominant cause the acute gastroenteritis caused by V. parahaemolyticus. Wound infections also occur, but are less common than seafood-borne disease. The disease mechanism of V. parahaemolyticus infections has not been fully elucidated.

Clincal isolates usually possess two pathogenicity islands (PAI), which are acquired via horizontal gene transfer. Although the pathogenicity islands have been sequenced, the functions of many of the PAI genes have not been elucidated. Each pathogenicity island contains a genetically-distinct Type III Secretion System, which is capable of injecting virulence proteins into host cells to cause disease. Additionally, two well-characterized virulence proteins are typically found in the pathogenicity islands, the thermostable direct hemolysin gene (tdh) or the tdh-related hemolysin gene (trh). Strains possessing the hemolysins exhibit beta-hemolysis on blood agar plates.

Epidemiology
Outbreaks tend to be concentrated along coastal regions during the summer and early fall when higher water temperatures favor higher levels of bacteria. Seafood most often implicated includes squid, mackerel, tuna, sardines, crab, shrimp, and bivalves like oysters and clams. The incubation period of ~24 hours is followed by explosive, watery diarrhea accompanied by nausea, vomiting, abdominal cramps, and sometimes fever. Vibrio parahaemolyticus symptoms typically resolve with-in 72 hours, but can persist for up to 10 days in immunocompromised individuals. As the vast majority of cases of V. parahaemolyticus food infection are self-limiting, treatment is not typically necessary. In severe cases, fluid and electrolyte replacement is indicated.

Additionally, swimming or working in affected areas can lead to infections of the eyes or ears and open cuts and wounds. Following Hurricane Katrina, there were 22 vibrio wound infections 3 of which were caused by V. parahaemolyticus and 2 of these led to death.

Hosts
Hosts of Vibrio parahaemolyticus include:
 * Clithon retropictus
 * Nerita albicilla