Page History

...

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

Genetic characteristics: Serovar Paratyphi A isolates have has been found to be resistant to flouroquinolones. A few isolates have been shown to be resistant to azithromycin polyphyletic with three lineages identified. Tanmoy et al. developed a genotyping tool, Paratype, based on single nucleotide polymorphisms (SNPs), which classifies Salmonella Paratyphi A into three main clades, nine sub-clades, and 18 genotypes. Each genotype is identified by a unique allele marker situated on an essential gene. Pereira-Dias et al. included a total of 117 serovar Paratyphi A isolates collected from an outbreak of enteric fever in Vadodara, India in their study, with the majority (72.6%) belonging to genotype 2.4.2, the predominant genotype worldwide. The remaining isolates were primarily genotype 2.3 (25.6%), while only two were identified as genotype 2.4.1. All outbreak isolates carried a single gyrA mutation linked to reduced fluoroquinolone susceptibility—74.35% had an S83F substitution, and the rest had an S83Y substitution. Rahman et al. studied serovar Paratyphi A isolated from enteric fever patients in Bangladesh from 2008 to 2018 and revealed that most serovar Paratyphi A isolates from Bangladesh (67.2%) belonged to the globally dominant lineage A, while the remaining isolates were distributed between lineages C (19.4%) and F (13.4%). The population structure exhibited minimal variation across different regions of the country. All Bangladeshi isolates carried point mutations in gyrA—either at codon 83 or 87—which are linked to reduced fluoroquinolone susceptibility. Additionally, they found a pHCM2-like cryptic plasmid closely related to plasmids found in Salmonella Typhi strains circulating in Bangladesh.

Jacob et al. suggested that genome degradation, gene acquisition, and loss are key drivers in the evolution of new serovar Paratyphi A lineages, with 10 pseudogene-forming mutations identified as potentially linked to lineage emergence. Pan-genome analysis highlights the insertion of P2/PSP3 phage in genotypes 2.3.2/2.3.3 and the acquisition of an IncX1 plasmid in genotype 1.2.2 as notable evolutionary events. Meanwhile, they identified six missense mutations in LPS biosynthesis genes, though structural predictions suggest these have minimal impact on lipopolysaccharide structure and likely do not affect vaccine effectiveness.

A review paper mentioned that unlike serovar Typhi, serovar Paratyphi A lacks the viaB locus and does not express the Vi capsule, instead evading antibody-mediated immunity through extended O-antigen chains. While SPI-1 expression and epithelial invasion are markedly reduced under aerobic conditions compared to microaerobic growth, serovar Paratyphi A uniquely exhibits enhanced SPI-2-dependent intracellular replication—a trait not observed in serovar Typhimurium. Genomic comparisons reveal distinct virulence gene profiles: SopE2 and CigR are exclusive to serovar Paratyphi A, whereas SteC, SifB, and SspH2 are specific to serovar Typhi.

Animal reservoir: Serovar Paratyphi A is host-restricted to humans.

...

1. https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(18)30685-6/fulltext
2. https://www.ncbi.nlm.nih.gov/books/NBK557513/
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC8609278/
4. https://wwwnc.cdc.gov/eid/article/23/5/15-1539_article
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC2798017/
6. https://pmc.ncbi.nlm.nih.gov/articles/PMC3367370/
7. https://www.cdc.gov/yellow-book/hcp/travel-associated-infections-diseases/typhoid-and-paratyphoid-fever.html#:~:text=In%202019%2C%20before%20the%20COVID,160%20cases%20of%20typhoid%20fever
8. https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2025.1547190/full
9. https://www.nature.com/articles/s41467-022-35587-6
10. https://pmc.ncbi.nlm.nih.gov/articles/PMC9973848
11. https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0009748
12. https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1010650
13. https://onlinelibrary.wiley.com/doi/10.1111/cmi.12939
14. https://www.sciencedirect.com/science/article/abs/pii/B9780128225219000319
15. https://pubmed.ncbi.nlm.nih.gov/37274527/
16. https://www.sciencedirect.com/science/article/pii/S0255085720301511?ref=pdf_download&fr=RR-2&rr=9426415809c0fbfb
17. https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0003859
18. https://pubmed.ncbi.nlm.nih.gov/24198224/
19. https://pmc.ncbi.nlm.nih.gov/articles/PMC6528785/
20. https://pubmed.ncbi.nlm.nih.gov/8714142/