Apparent expansion of virulent Vibrio parahaemolyticus in humans and sea otters

Vibriosis is the most important public health threat from seafood consumption and marine recreation. Pathogenic Vibrio spp. employ virulence factors, including hemolysins and secretion systems, frequently detected in human cases, but virulence data in northern and southern sea otters (Enhydra lutris kenyoni and E. l. nereis, respectively) are limited despite their potential as marine bioindicators. Genomic epidemiology was used to characterize virulence factors of Vibrio spp. genomes (n = 570), including V. alginolyticus (n = 55), V. diabolicus (n = 52), non-O1/O139 V. cholerae (n = 163), and V. parahaemolyticus (n = 287) collected in North America (2000–2019). Virulence factors of V. parahaemolyticus were compared between isolation sources: bivalves, environment, humans, and southern and northern sea otters. Hemolysins (tdh, trh) and type III secretion system 2 (T3SS2) gene prevalences were lowest in environmental isolates, while tdh and T3SS2 gene prevalences were higher in human and northern sea otter isolates than those from southern sea otters. A hemolysin allele (trh1) was detected almost exclusively in human and sea otter isolates. Despite V. parahaemolyticus genomic diversity, detected genomic clusters were comprised of highly related and tdh+/trh+ genomes from nonenvironmental sources including humans and sea otters. Observed pathology in Vibrio spp. positive sea otters frequently included septicemia, enteritis, and moderate-to-severe melena. Co-occurrence of T3SS2 and T6SS1 in V. parahaemolyticus was associated with pathological findings and ampicillin-susceptible genotypes, suggesting a trade-off between virulence and antimicrobial resistance. Based on these findings, V. parahaemolyticus undergoes selection pressures resulting in apparent expansion, i.e. genomic clustering, of tdh+/trh+ virulent strains infecting humans and sea otters.