A one health approach in the epidemiology of campylobacter and salmonella: the continnum seabirds - humans
- Autores: Elisabet Moré Mir
- Directores de la Tesis: Marta Cerdà Cuéllar (dir. tes.), Joaquim Segalés Coma (tut. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Natàlia Majó i Masferrer (presid.), Virginia Aragón Fernández (secret.), Carlos Balsalobre Parra (voc.)
- Programa de doctorado: Programa de Doctorado en Medicina y Sanidad Animales por la Universidad Autónoma de Barcelona
- Materias:
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- Resumen
Zoonotic thermophilic Campylobacter spp. and nontyphoidal Salmonella enterica are a major cause of foodborne human gastroenteritis worldwide. Both bacteria are able to infect a broad range of domestic and wild animals. A wide variety of wild birds, especially gulls, have been reported as asymptomatic carriers of these zoonotic agents in Europe, America and Australia. However, there is scarce information about these reservoirs in Africa and remote regions of the Southern Ocean, and the role of wild birds in the epidemiology of these pathogens is not fully understood. Thus, within the framework of this PhD thesis we have investigated the occurrence, antimicrobial susceptibility, virulence potential and population structure or genetic diversity of Campylobacter and Salmonella spp. in seabird species along the western coast of South Africa (near the Benguela Upwelling Region) and across the Antarctic and Subantarctic region. We have also analysed the genetic relation and virulence potential of isolates of Salmonella serovars from seabirds, poultry and humans, to assess whether common strains are circulating among different niches in Southwestern Europe.
In Western Cape (South Africa), we detected thermophilic Campylobacter spp., mainly C. jejuni, in kelp gulls and greater crested terns with similar prevalences. Most C. jejuni sequence types (ST)s belonged to the clonal complex (CC)-1275, which is mainly related to aquatic environments and wild birds. On the contrary, a higher occurrence of Salmonella was observed in kelp gulls than in greater crested terns, which seems to be related to the scavenging feeding habits of the former. Anatum, Enteritidis and Hadar were the most frequent Salmonella serovars, although a great diversity of other zoonotic serovars were found, especially in gull colonies near urban areas. The same or highly similar pulsed-field gel electrophoresis genotypes (pulsotypes) were detected in some Salmonella isolates from seabirds and humans presenting with salmonellosis in Cape Town hospitals. Most S. Enteritidis and S. Typhimurium isolates belonged to ST-11 and ST-34, respectively, which are genotypes globally distributed in a broad range of hosts. In addition to virulence potential, both Campylobacter and Salmonella isolates exhibited antimicrobial resistance to several agents, including critically important antimicrobials (quinolones, tetracyclines and β-lactams), and multidrug resistance in Salmonella serovars from kelp gulls.
Thermophilic Campylobacter spp. were also found in all sampled Antarctic and Subantarctic islands, mainly C. lari, but also C. jejuni, specially in brown skuas, one of the main opportunistic seabird species in the Southern Ocean region. It is noteworthy that C. jejuni CC-21, CC-45 and CC-206, associated to domestic animals and human infections, were isolated. However, Salmonella (mainly S. Enteritidis ST-11) was only isolated from a few seabirds at Livingston Island (Antarctic Peninsula) suggesting this bacterium is not indigenous to the region. The presence of C. jejuni and S. Enteritidis genotypes commonly found in humans and domestic animals, suggests reverse zoonosis (from humans to seabirds) probably through tourism and scientific activities. Nevertheless, this pathogens introduction to remote regions by other sources, such as the migration movements of seabirds, cannot be ruled out. We also show further spread of the bacteria among Antarctic wildlife is facilitated by substantial connectivity among populations of opportunistic seabirds, notably skuas.
On the other hand, in seagulls from Southwestern Europe we identified a high diversity of exclusive Salmonella pulsotypes (mainly S. Typhimurium) compared to the more predominant pulsotypes from poultry and humans, which likely indicates that seagulls are exposed to a higher variety of contamination sources. However, we detected 30 pulsotypes in common among isolates from two or three different host niches belonging to 12 different serovars: Bredeney, Derby, Enteritidis (ST-11), Grumpensis, Hadar, Infantis, Kentucky, Kottbus, Mikawasima, Rissen, Typhimurium (ST-19 and ST-34) and Virchow. This finding suggests the existence of generalist Salmonella strains circulating among different compartments. In addition, the presence of a wide repertoire of virulence-associated genes, regardless of the host of origin, may increase the capacity of these strains to infect different hosts and to adapt to new environments.
Our results demonstrate that seabirds can be carriers of Campylobacter and Salmonella strains of anthropogenic origin, some of them showing antimicrobial resistance and an important virulence potential. Our findings support that seabirds contribute to the amplification and maintenance of these pathogens in the environment. In addition, given the foraging and migratory movements of seabirds, they may play an important role in the spread of these zoonotic agents, but also of resistance and virulence genes by mobile genetic elements, to remote geographical areas and new animal hosts. It is necessary to increase the surveillance systems to wildlife, especially in seabirds, and to establish stricter environmental policies for the management of human wastes to limit the access of these birds to anthropogenic sources of contamination, which may help to control the dissemination of strains with potential hazard for the public and animal health.
