Oral uptake of pathogen: A relatively large number of organisms (∼ 105) is needed to cause infection (high infective dose), unlike, e.g., in Shigella infection, where as few as ∼ 10 organisms suffice to infect the host.
Migration into the Peyer patches of the distal ileum: If the pathogen manages to reach the distal ileum, it migrates via M cells through the epithelium and into the Peyer patches.
Infection of macrophages → nonspecific symptoms
Spread from macrophages to the bloodstream → septicemia → systemic disease
Migration back to intestine → excretion in feces
Clinical features
Week 1
Body temperature rises gradually.
Relative bradycardia (not seen in children)
Physiologically, the heart rate increases in proportion to body temperature (for every degree Fahrenheit, the heart rate should increase ∼ 10 beats/min). In typhoid fever, this physiological response is typically reduced. Thus, the heart rate is only moderately increased despite a high fever, which is known as relative bradycardia.