S. Weltevreden¶

At a Glance


Antigenic Formula	`3,{10}{15}:r:z6`
Serogroup	O:3,10 (E1)
NCBI Pathogen Detection	View isolates

Background Information¶

Salmonella enterica subsp. enterica serovar Weltevreden (antigenic formula 3,{10}{15}:r:z₆) is a serovar of the O:3,10 (E₁) serogroup. Serovar Weltevreden has been reported to cause myocarditis in a case from South India. In Malaysia, serovar Weltevreden became a more frequent cause of human gastroenteritis, representing 31% of all detected serovars from 1989 to 1994. Tran et al. reported a low prevalence of serovar Weltevreden in domestic chickens, ducks, and pigs in the Mekong Delta. The rising association between serovar Weltevreden and human salmonellosis cases in Southeast Asia aligns with its frequent isolation in the region's seafood.

Genetic Characteristics¶

Serovar Weltevreden has been found to be monophyletic. A clonal group of serovar Weltevreden isolated in farmed shrimp from Vietnam’s Mekong Delta showed susceptibility to most tested antimicrobials, though some isolates exhibited resistance to florfenicol, chloramphenicol, sulfamethoxazole, or trimethoprim. However, all serovar Weltevreden isolates (100%) collected from wild geckos in Cambodia, Thailand and Vietnamwere were pan-susceptible. An India study found that all Salmonella Weltevreden strains isolated in their study carried virulence genes associated with Salmonella Pathogenicity Islands (SPIs), including invA/E, orgA, ttrC, ssaQ, mgtC, misL, and spi4D), as well as the enterotoxin gene (stn) and the hyperinvasive locus gene (hilA). With the exception of erythromycin resistance, all strains showed susceptibility to standard antimicrobials used in diarrhea treatment.

All sequenced serovar Weltevreden isolates in a Danish study collected from cultured shrimp and tilapia in Vietnam and China belonged to ST365 and carried key virulence genes located within SPI 1–5. Ten isolates possessed the IncFII(S) plasmid, similar to the virulence-associated plasmid pSPCV found in S. Paratyphi C, while one isolate contained an IncQ1 plasmid co-located with resistance genes (strA/B, sul2, tetA), similar to the IncQ1-type plasmid pNUC in S. Typhimurium. Pangenome analysis identified 7,891 genes, with a core genome of 4,892 genes, showing highly similar accessory genomes between clinical and environmental isolates. Additionally, serovar Weltevreden featured unique genomic regions containing glpX (class II fructose-1,6-bisphosphatase), rfbC (dTDP-4-dehydrorhamnose 3,5-epimerase), and cmtB (mannitol-specific PTS enzyme IIA component), which are involved in carbohydrate biosynthesis pathways.

Zhang et al. revealed that most serovar Weltevreden strains from diarrheal patients in China (97.92%, 94/96) and other global regions (94.97%, 189/199) belonged to ST 365. The remaining strains in their study were identified as ST3771 (n=3), ST22 (n=1), ST155 (n=1), and ST684 (n=1). Additionally, ST365 was commonly found in animals, food, and environmental samples worldwide. These serovar Weltevreden strains harbored multiple virulence genes, and a 100.03-kb IncFII(S) plasmid was frequently present. Removing this plasmid reduced the bacteria's ability to infect Caco-2 cells and C57BL/6 mice. Interestingly, a study found that serovar Weltevreden exhibits higher expression of the enterotoxin stn gene when cultured in seafood.

Animal Reservoir¶

Wild geckos are likely to be the reservoir for serovar Weltevreden. Serovar Weltevreden was also frequently reported from seafood.

Geographical Distribution¶

Serovar Weltevreden has been found worldwide. Over the past 20 years, Salmonella Weltevreden has become a predominant serovar, particularly in Southeast Asia, including countries such as Oman, Singapore, China, Thailand, Vietnam, and India.

Human/Animal Outbreaks¶

Year	Location	Associated source	Number of cases
2021	US: multistate	Frozen pre-cooked shrimp	9
2019	Australia	Frozen microwave meals	46
2017-2018	US: multistate	Kratom¹	199
2015	US: multistate	Frozen tuna	65²
2015	Oman	Hummus (likely)	101
2010	India	Food comprising milk, rice, sprouted pulses and curd	150 (8 confirmed)
2007	France	Unknown	26
2007	Europe: multinational	Alfalfa sprouts	45

¹ Multiple serovars including Salmonella I 4,[5],12:b:-, Heidelberg, Javiana, Okatie, Weltevreden, and Thompson were involved in this outbreak. The case number here does not reflect the number of infections linked to Salmonella Weltevreden only.

² Sixty-five individuals across 11 states were reported infected with outbreak strains, including 64 cases of Salmonella Paratyphi B variant L(+) tartrate(+) and 1 case of Salmonella Weltevreden.

Border Rejections¶

There have been no recent border rejections linked to this serovar.

Recalls¶

Year	Location	Recalled product	Type
2024	Finland	Turmeric powder from India	Herbs and spices
2023	US: multistate	Black fungus¹	Other food product / mixed
2023	Germany	Dried Mu-Err mushrooms from Vietnam, via Czech Republic	Other food product / mixed
2021	US: multistate	Frozen pre-cooked shrimp²	Crustaceans and products thereof
2019	Australia	Frozen microwave meals³	Other food product / mixed
2007	Denmark, Norway, Finland	Alfalfa sprouts⁴	Fruits and vegetables

¹ Multiple Salmonella serovars including Salmonella Javiana, Mgulani and Weltevreden were found. AH USA Group Inc. issued a recall of its Black Fungus (Nam Meo) product.

² This recall was caused by a multistate outbreak described above. Avanti Frozen Foods of India expanded its voluntary recall of frozen cooked shrimp on August 13, 2021. The expansion now includes products imported into US from November 2020 through May 2021.

³ This recall was caused by a multistate outbreak described above. Core Ingredients issued a recall for eight frozen pre-prepared meals with best-before dates ranging from March 5, 2020, to October 4, 2020.

⁴ This recall was caused by a multi-country outbreak described above.