Typhoid toxin: reframing enteric fever

SUMMARYSalmonella enterica serovars Typhi and Paratyphi A cause enteric (typhoid/paratyphoid) fever, a systemic disease that remains a major source of morbidity and mortality worldwide. The most distinctive clinical manifestations, such as sustained fever with relative bradycardia, leukopenia, neuropsychiatric symptoms/encephalopathy, and ileal perforation, have long lacked a unifying mechanistic explanation. Over the past two decades, studies of typhoid toxin have reframed how we understand this disease. Typhoid toxin is a human-adapted, chimeric A₂B₅ exotoxin assembled exclusively inside infected cells. It couples an ADP-ribosyltransferase (PltA) and a DNase I-like nuclease (CdtB) on a pentameric delivery ring (PltB or the alternate, PltC), that recognizes N-acetylneuraminic acid (Neu5Ac)-terminated human sialoglycans. The toxin is produced by bacteria residing within the Salmonella-containing vacuole (SCV), secreted across the bacterial envelope into the SCV lumen by a phage-derived pathway now classified as type 10 secretion system, sorted for export by the host CI-M6PR/COPII trafficking machinery, and then re-enters distant target cells via retrograde transport to the endoplasmic reticulum (ER). Recent work has linked typhoid toxin to leukopenia, blood-brain barrier disruption causing encephalopathy, gut-vascular and immune dysfunction leading to intestinal perforation, and hepatobiliary injury. The discovery of an alternate B-subunit (PltC) established a paradigm of modular B-subunit exchange that diversifies receptor usage, tissue tropism, and biology. Collectively, these insights redefine typhoid fever as a toxin-driven immunovascular disease and identify actionable targets for neutralizing antibodies and barrier-protective therapies.