Table 1.
Summary of the differences between NTS and typhoidal serovars associated with disease in humans.
| NTS serovars | Typhoidal serovars | |
|---|---|---|
| Serovars | Represented by the ubiquitous serovars Typhimurium and Enteritidis, but ∼1500 other serovars of S. enterica ssp. I are known | Typhi, Paratyphi, and Sendai |
| Host range | Broad | Human-restricted |
| Epidemiology | Worldwide | Endemic in developing countries especially Southeast Asia, Africa, and South America |
| Reservoirs | Farm animals, produce, pets | None, human to human transmission |
| Clinical manifestations | Self-limiting gastroenteritis in immunocompetent individuals (diarrhea, vomiting, cramps)In immunocompromised patients (including patients with inherited deficiency of the IL-12/IL-23 system and HIV), disease is associated with invasive extraintestinal infections | Invasive, systemic disease in immunocompetent individuals (fever, chills, abdominal pain, rash, nausea, anorexia, hepatosplenomegaly, diarrhea or constipation, headache, dry cough) |
| Disease course | Short incubation period (6–24 h) Brief duration of symptoms (less than 10 days) Long-term carriage has not been observed | Long incubation period (7–21 days) Extended duration of symptoms (up to 3 weeks) One to four percent of infected individuals become long-term (≥1 year) carriers |
| Human immune response | Robust intestinal inflammation, neutrophil recruitment, Th1 response | Minimal intestinal inflammation, leukopenia, Th1 response |
| Genetic basis of disease differences and host specificity | Low degree of genome degradation Able to use terminal electron acceptors for anaerobic respiration in the inflamed gut Unique virulence factors (e.g., fimbriae, SPI-14) | ∼5% of the genome is degraded (e.g., inactivated metabolic and virulence factor genes) Unique virulence factors and pathogenicity islands (e.g., Vi antigen, SPIs 7, 15, 17, and 18) |
| Vaccination | No vaccine available for humans | (i) killed whole cell parenteral vaccine, (ii) live attenuated oral vaccine (Ty21a), (iii) Vi polysaccharide capsule-based vaccine |
| Animal models of human disease | Streptomycin-pretreated mice Calves Non-human primates | Mouse infection with S. Typhimurium Tlr11-/- mice Humanized mice |