Abstract / Description of output
Passerine salmonellosis is a well-recognised disease of birds in the order Passeriformes, including common songbirds such as finches and sparrows, caused by infection with Salmonella enterica serovar Typhimurium. Previous research has suggested that some subtypes of S. Typhimurium - definitive phage types (DT) 40, 56 variant, and 160 - are host-adapted to passerines, and that these birds may represent a reservoir of infection for humans and other animals. Here, we have used whole genome sequences of 11 isolates from British passerines, five isolates of similar DTs from humans and a domestic cat, and previously published S. Typhimurium genomes including similar DTs from other hosts to investigate the phylogenetic relatedness of passerine salmonellae in comparison with other S. Typhimurium, and investigate possible genetic features of the distinct disease pathogenesis of S. Typhimurium in passerines. Our results demonstrate that the 11 passerine isolates and 13 other isolates, including those from non-passerine hosts, were genetically closely related, with a median pairwise single nucleotide polymorphism (SNP) difference of 130 SNPs. These 24 isolates did not carry antimicrobial resistance genetic determinants or the S Typhimurium virulence plasmid. Although our study does not provide evidence of Salmonella transmission from passerines to other hosts, our results are consistent with the hypothesis that wild birds represent a potential reservoir of these Salmonella subtypes, and thus, sensible personal hygiene precautions should be taken when feeding or handling garden birds.
IMPORTANCE: Passerine salmonellosis, caused by certain definitive phage types (DTs) of Salmonella Typhimurium, has been documented as a cause of wild passerine mortality since the 1950s in many countries, often in the vicinity of garden bird feeding stations. To gain better insight into its epidemiology and host-pathogen interactions, we genome-sequenced a collection of eleven isolates from wild passerine salmonellosis in England and Wales. Phylogenetic analysis showed these passerine isolates to be closely related to each other and to form a clade distinct from other strains of S Typhimurium, which included a multidrug resistant isolate from invasive non-typhoidal Salmonella disease which shares the same phage type as several of the passerine isolates. Closely related to wild passerine isolates and within the same clade were four S Typhimurium isolates from humans as well as isolates from horses, poultry, cattle, an unspecified wild bird, and a domestic cat and dog with similar DTs and/or multi-locus sequence types. This suggests the potential for cross-species transmission and the genome sequences provide a valuable resource to investigate passerine salmonellosis further.