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Recent studies reveal that the Rab GTPase Rab32 and its guanine nucleotide exchange factor BLOC-3 form a conserved pathway that both restricts Salmonella Typhi to human hosts and mediates its killing in macrophages of non-susceptible species. These proteins, previously recognized for their role in intracellular membrane trafficking—particularly in melanin synthesis through enzyme transport to melanosomes—are now identified as central players in innate immunity against typhoidal Salmonella. Following intestinal invasion, serovar Typhi effectively evades host defenses through multiple mechanisms: it avoids TLR4 recognition, escapes the classical complement pathway, and resists oxidative killing—primarily through production of its protective Vi capsular polysaccharide.  More specifically, the TviA regulatory protein orchestrates key virulence strategies through its dual regulatory function: (1) suppressing flagellin-induced inflammatory responses and (2) activating expression of the immunoevasive Vi capsular polysaccharide. These virulence factors are encoded within SPI-7, which harbors the viaB locus (Vi capsule genes) along with additional pathogenicity determinants including type III secretion system, SopE and a type IVB pilus assembly system.

Animal reservoir: Salmonella Typhi is a human-restricted serovar.

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