Reported outbreaks of Vibrio parahaemolyticus have increased worldwide, particularly in regions of high seafood consumption. In Mozambique, seafood constitutes an important food resource and diarrheal diseases are common among its inhabitants. Edible clams were collected in Maputo Bay during both the dry and rainy seasons, with the results showing the number of viable counts of vibrios in clams to peak during the latter. Vibrio parahaemolyticus was the predominant species identified among the isolated strains. Although only one of 109 total strains carried the tdh virulence gene, 69% of isolates showed evidence of hemolytic capacity when subjected to a functional test. Similar virulence patterns and biochemical properties were found in strains isolated from Indian and Swedish marine waters. Antibiotic resistance was, however, more pronounced in strains isolated from these latter two environments.

During the summer of 2006, several wound infections - of which three were fatal caused by Vibrio cholerae were reported from patients who had been exposed to water from the Baltic Sea. Before these reports, we initiated a sampling project investigating the occurrence of potential human pathogenic V. cholerae, Vibrio vulnificus and Vibrio parahaemolyticus in The Sound between Sweden and Denmark. The Blue mussel (Mytilus edulis) was used as an indicator to follow the occurrence of vibrios over time. Molecular analyses showed high frequencies of the most potent human pathogenic Vibrio spp.; 53% of mussel samples were positive for V. cholerae (although none were positive for the cholera toxin gene), 63% for V. vulnificus and 79% for V. parahaemolyticus (of which 47% were tdh(+) and/or trh(+)). Viable vibrios were also isolated from the mussel meat and screened for virulence by PCR. The mortality of eukaryotic cells when exposed to bacteria was tested in vivo, with results showing that the Vibrio strains, independent of species and origin, were harmful to the cells. Despite severe infections and several deaths, no report on potential human pathogenic vibrios in this area had been published before this study.

Vibrio cholerae may cause diarrheal diseases and wound infections, both of which have the potential to be fatal. Transmission to humans is often linked to consumption of contaminated shellfish/drinking water or dermal exposure to water (e.g. when swimming). In this study, we investigated whether different isolates of Vibrio cholerae differ in terms of accumulation, persistence, and viability when encountering blue mussels (Mytilus edulis). Mussel uptake and elimination of three different V. cholerae strains were compared: one fatal clinical non-O1/O139 isolate, one highly potent El Tor biotype, and one marine strain isolated from blue mussels. The results showed that the uptake of the marine strain was significantly higher than the clinical strain, but the elimination process of the marine strain was also more efficient. The El Tor strain was not at all ingested by the mussels. In addition, the survival of bacteria when incubated together with M. edulis hemocytes was tested in vitro. The viability of clinical strains was unaffected by the presence of hemocytes, and the marine strains were even more resistant and able to multiply. We conclude that the highly virulent El Tor biotype was not taken up by the mussels and could thereby escape the mussels' elimination process. The potentially fatal non-O1/O139 V. cholerae strain may accumulate in low numbers, but could be very persistent in mussels.