Urbanized white ibises (Eudocimus albus) are carriers of Salmonella enterica: what is the significance to public health and wildlife?

Wild birds adapted to urban environments have different opportunities for pathogen exposure, infection, and transmission compared to their natural conspecifics. Food provisioning by people may influence these factors,... [ view full abstract ]

Wild birds adapted to urban environments have different opportunities for pathogen exposure, infection, and transmission compared to their natural conspecifics. Food provisioning by people may influence these factors, especially when high-density mixed species flocks aggregate. White Ibises (Eudocimus albus), an iconic Everglades species in decline in Florida, are becoming increasingly common in urbanized areas of south Florida where most are hand-fed. We examined the prevalence of Salmonella shedding by ibises to determine the role of landscape characteristics where ibis forage in shedding rates. We also compared Salmonella isolated from ibises to human isolates to better understand non-foodborne human salmonellosis. From 2010-2013, 13% (n=261) adult/subadult ibises and 35% (n=72) nestlings sampled were shedding Salmonella. The prevalence of Salmonella shedding by ibises significantly decreased as the percent of wetlands and grasslands increased, and increased as the proportion of parks, lawns, golf courses and similar land cover types increased, suggesting that natural ecosystem land cover types supported birds with a lower prevalence of infection. A high diversity of Salmonella serovars and strain types were shed by ibises, with 33% ranked in the top 20 of high significance for people. Importantly, 44% of the Salmonella Pulsed-Field Gel Electrophoresis patterns for ibis isolates (n=43) matched profiles in the CDC PulseNet USA database. Of these, 20% came from Florida in the same three years we sampled ibis. Most importantly, there was a negative relationship between the amount of emergent wetland and the number of Salmonella isolates from ibises that matched human cases in the PulseNet database. Together, our results indicate that ibises are good indicators of salmonellae strains circulating in their environment and they have both the potential and opportunity to transmit salmonellae to people. Finally, they may act as salmonellae carriers to natural environments where other more highly-susceptible groups (nestlings) may be detrimentally affected.