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Background: Salmonella enterica subsp. enterica serovar Virchow (antigenic formula 6,7,14:r:1,2) is a serovar of the O:7 (C₁) serogroup. S. Virchow is a serovar adapted to poultry, but also isolated from foodborne outbreaks not directly traced back to chicken products. A 2010 report from Switzerland reported that S. Virchow was one of the 5 most common Salmonella serovars in Europe, with reports of 3^rd-generation cephalosporin- and fluoroquinolone-resistance. Most often, S. Serovar Virchow was first isolated from a patient with a typhoid-like illness in 1930 by Kaufmann. This serovar has been reported to infect a infant that was transmitted by the household dogs. The ranking of serovar Virchow compared to other Salmonella serovars ranged from 4th to 8th place in Switzerland. Annual incidence rates demonstrated minor change during this period, declining from 0.45 per 100,000 people in 2004 to 0.40 per 100,000 in 2009. Children under 5 years of age showed a seven times higher Salmonella Virchow infection rate compared to those above 5 years. In South-East Asia, Europe, and Oceania, serovar Virchow is consistently found within the top 20 Salmonella serovars. Most often,serovar Virchow infection causes gastrointestinal illness, but a 1984 report from Essex, England identified septicemic patients who suffered from neurological symptoms. The clone corresponding to the 2017 multi-country outbreak has been circulating in the EU poultry meat production chain at least in France, Germany, Ireland, and the Netherlandshowever, in Israel and other countries including US, human infections occur infrequently but demonstrate a high propensity for invasive manifestations.

NCBI PD link for serovar Virchow: https://www.ncbi.nlm.nih.gov/pathogens/isolates/#(taxgroup_name:%22Salmonella%20enterica%22)%20AND%20computed_types:(%22serotype=Virchow%22)

Genetic characteristics: Serovar Virchow has been found to be polyphyletic with two lineages identified. Weinberger et al. revealed that only 6% of serovar Virchow isolates in their study were sensitive to all ten antibiotics evaluated. Resistance patterns varied, with 34% resistant to one antibiotic, 54% resistant to one to three agents, and 40% resistant to four to six agents. Notably, a substantial proportion of isolates showed resistance to nalidixic acid (89%), streptomycin (56%), tetracycline (43%), trimethoprim-sulfamethoxazole (38%), and chloramphenicol (28%). However, none exhibited resistance to ciprofloxacin or ceftriaxone. Similarly, a Swiss study found that 48 serovar Virchow isolates (32%) showed resistance to 1-3 antibiotics, with a higher proportion (54 isolates, 36%) displaying resistance to more than three drugs. Resistance patterns remained stable throughout the study period (2004-2009). Nalidixic acid resistance was prevalent (62%), strongly suggesting concurrent decreased fluoroquinolone susceptibility. Ciprofloxacin showed intermediate resistance, and ESBL production was rare (2 isolates).

In an in-vivo study, after oral infection of 7-day-old chicks, Salmonella Virchow colonized both the gut and spleen. This infection triggered increased specific IgA, IgG, and IgM antibodies, along with changes in leukocyte populations (CD3, CD4, CD8α, CD8β, MHC II, KuL01, γδ TCR positive cells) locally and systemically. Elevated expression of the pro-inflammatory cytokines IL-1β and IL-6 and the chemokine CXCLi2 was also observed. While primary infection of S. Virchow provided limited systemic protection against re-infection with itself or S. Typhimurium, it failed to protect against cecal colonization.

Wang et al. used whole-genome sequencing and identified the emergence of monophasic Salmonella Virchow variant (serotype 6,7,14:r:-). This phenotype resulted from replacement of the fljAB operon with a 4.8-kb E. coli cassette, abolishing phase-2 flagellar antigen expression. Compared to 16 published serovarVirchow genomes, these two isolates possess a unique CRISPR type (VCT12) and show closest genetic relatedness to serovarVirchow strains BCW_2814 (Denmark) and BCW_2815 (China). Additionally, acquisition of Salmonella Genomic Island 2 (SGI2) harboring an antimicrobial resistance gene cassette conferred multidrug resistance to chloramphenicol, tetracycline, trimethoprim, and sulfamethoxazole.

Animal reservoir: Poultry is the main reservoir for serovar Virchow.

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³ This recall was caused by a multistate outbreak described above. Garden of Life, LLC extended its recall of RAW Meal Organic Shake & Meal chocolate, original, vanilla, and vanilla chai products on February 12, 2016, adding more lots to the list.

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