Infectious Diseases 2021

Infectious Diseases 2021

Salmonella Infantis in Dutch broiler flocks

Veterinary Microbiology 258 (2021) 22 May, 2021

Since 2014, S. Infantis has been the most commonly isolated serovar in broilers in the Netherlands, accounting for 78% of all Salmonella isolates from broilers reported in 2018. Also Europe-wide, S. Infantis is currently the most common serovar in broilers (46–57 %) and broiler meat (37–51 %),and its prevalence has increased in breeding flocks as well. Moreover, S. Infantis ranked fourth among the serovars isolated from human salmonellosis cases in the Netherlands and in Europe in the past few years, after S. Enteritidis, S. Typhimurium and its monophasic variant. In 2014, a multi-drug resistant S. Infantis strain was identified in Israel carrying a mega-plasmid of approximately 300 Kb named pESI (plasmid of emerging S. Infantis).
Researchers from the Netherlands investigated the prevalence, genetic characteristics and risk factors for (pESI-carrying) S. Infantis in broilers. Faecal samples from 379 broiler flocks (in 198 farms with ≥3000 birds) in the Netherlands were tested. Sampling was performed in July 2018-May 2019, three weeks before slaughter. Fourteen flocks (in 10 farms) were S. Infantis-positive, resulting in a 3.7 % flock-level and 5.1 % farm level prevalence. All but one isolate carried a pESI-like mega-plasmid. The typical pESI-borne multi-resistance pattern to aminoglycosides, sulphonamide and tetracycline (93 %), as well as trimethoprim (71 %), was found. S. Infantis was found more often in flocks using salinomycin as coccidiostat, where flock thinning was applied or litter quality was poor, whereas employing external cleaning companies, wheat in feed, and vaccination against infectious bronchitis, were protective. Suggestive evidence for vertical transmission from hatcheries was found.