Which Salmonella serotype is found exclusively in humans?

• A. Typhi
• B. Paratyphi A
• C. Enteritidis
• D. Typhimurium

Answer: (A)

Salmonella Typhi is the serotype that is found exclusively in humans because it is adapted to the human host and has no significant animal reservoir. It causes typhoid fever, a systemic illness transmitted mainly from person to person through the fecal-oral route, which is why you don’t see this serotype circulating in animals.

In contrast, the other serotypes listed are associated with a wide range of animal hosts and typically cause gastroenteritis in humans when they are transmitted, often through contaminated food or water from animal sources. This difference in host range—human-restricted for Typhi versus zoonotic for the others—explains why Typhi is the correct choice for an exam asking which serotype is found exclusively in humans.