Infectious Diseases 2023

There were 2,404 isolations of Salmonella from chickens in 2022 an increase of 43.9 % compared with 2021 (1,671 isolations) and the highest number of isolations since before 2009. Salmonella isolations from chickens increased substantially between 2018-2020 compared to the previous years (approximately 50% year on year). This overall rise was primarily the result of increased isolations in the broiler sector and is possibly linked to the ban on using formaldehyde based products in animal feed production since January 2018, across the EU and more recently in retained Great Britain legislation, as well as emergence of strains that are more persistent in farms and hatcheries.
Forty-five different Salmonella serovars were isolated in 2022, accounting for 2,356 of the 2,404 isolations. Forty-eight isolations involved untypable Salmonella cultures (including 18 rough strains).
Salmonella Mbandaka was the most frequently isolated serovar in 2022 (695 isolations, 28.9% of all chicken isolations) having increased by over two-fold compared to 2021 (294 isolations). Isolations of S. Mbandaka, which is a feed related serovar associated with soya products, had been generally increasing since 2010 peaking in 2018 (472 isolations, 25.7% of all chicken isolations) when it was the most frequently isolated serovar.
There were 460 isolations of S. Montevideo in 2022 accounting for 19.1% of all chicken isolations and the second most frequently isolated serovar compared to the most frequently isolated in 2021 (403 isolations, 24.1% of all chicken isolations).
In 2022 there were 343 isolations of Salmonella 13,23:i:- accounting for 14.3% of all Salmonella isolations and making it the third most frequently isolated serovar, consistent with 2021. There is increasing evidence that Salmonella 13,23:i:- strains represent a monophasic variant of S. Idikan with a mutation that prevents expression of the phase 2 flagella antigens. This serovar is associated with contaminated feed mills and can also become established and persistent in hatcheries and on poultry farms. Isolations of S. Agona from chickens increased by more than three-fold in 2022 (128 isolations) compared to 2021 (34 isolations). This is the highest number of isolations of this serovar ever reported.
Other notable increases in serovars isolated from chickens in 2022 compared with 2021 included S. Infantis (98 versus 42 isolations), S. Enteritidis (23 versus 9 isolations), the monophasic Salmonella Typhimurium variant Salmonella 4,5,12:i:- (18 versus 8 isolations).
The National Control Programme (NCP) for Salmonella in laying hen flocks:
The NCP for Salmonella in laying flocks includes all commercial egg laying holdings with 350 or more birds. Five adult flocks from 4 separate holdings tested positive for S. Enteritidis. Five adult flocks, from 4 separate holdings, tested positive for S. Typhimurium. The prevalence of all the serovars was 1.13%, and it was 0.27% for the regulated serovars. In 2022 the most common Salmonella serovar in adult laying hen flocks was S. Mbandaka accounting for 14.3% of total isolations, followed by S. Enteritidis (11.9%) and S. Typhimurium (11.9%).