zoonoses and communicable diseases common to ... - PAHO/WHO

138 BACTERIOSESFOOD POISONING CAUSED BYVIBRIO PARAHAEMOLYTICUSICD-10 A05.3 foodborne Vibrio parahaemolyticus intoxicationEtiology: Vibrio parahaemolyticus, belonging to the family Vibrionaceae, is agram-negative, motile, curved or straight bacillus that does not produce spores. It isa halophile that develops best in media with 2% to 3% sodium chloride but can multiplyin an 8% concentration of this salt. In most cases, isolated strains are ureasenegative, but urease-positive strains are also found; this difference may serve as anepidemiological marker.Based on O (somatic) and K (capsular) antigens, 20 O groups and 65 K serotypesare serologically distinguished. Most clinical strains can be typed, but environmentalstrains cannot.Many clinical strains of V. parahaemolyticus cultured in Wagatsuma agar (whichcontains human red blood cells) are beta-hemolytic, while environmental isolatesfrom water are not. This has been called the Kanagawa phenomenon or test. Giventhe difference in hemolytic capacity between clinical and environmental strains, itwas assumed that hemolysin is a virulence factor. This toxin is called thermostabledirect hemolysin (TDH). However, it has been demonstrated that TDH-negativestrains can cause disease and produce an immunologically related toxin, thermostablerelated hemolysin (TRH), with very similar properties. The twohemolysins are coded by two different genes. In some strains, it was possible to findboth hemolysins. Of 112 V. parahaemolyticus strains studied, 52.3% had the TDHgene alone, 24.3% had the TRH gene, and 11.2% had both genes (TDH and TRH).It can thus be stated that TDH and TRH are important factors in virulence (Shirai etal., 1990). In addition, strains from diarrhea patients producing TRH were comparedwith environmental strains of V. parahaemolyticus (isolated from seawater orseafood) producing TRH. The results show that they were indistinguishable (Yoh etal., 1992).Pili are another important factor in intestinal colonization and thus in virulence.Various researchers have shown that pili attach to rabbit intestinal epithelium andthat adhesive capacity is blocked by treating the vibrios with anti-pilus antibodies(Fab fraction). This does not produce an antihemolysin serum (Nakasone andIwanaga, 1990 and 1992; Chakrabarti et al., 1991).Geographic Distribution: V. parahaemolyticus has been isolated from sea andestuary waters on all continents. The agent’s distribution shows marked seasonalvariations in natural reservoirs. During cold months, it is found in marine sediment;during warm months, it is found in coastal waters, fish, and shellfish (Benenson,1990). There have been a few reports of the isolation of V. parahaemolyticus fromcontinental waters and fish in rivers or lakes. It is assumed that these waters had ahigh concentration of sodium chloride, which would allow the agent to survive(Twedt, 1989). The factors that determine the abundance of the bacteria includewater temperature, salinity, and plankton, among other factors.The countries most affected by the disease are Japan, Taiwan, and other Asiancoastal regions, though cases of disease have been described in many countries andon many continents.