Final answer:
Typhoid fever is caused by S. typhi, a bacteria that can persist without symptoms in carriers, who then spread it through fecal contamination. Asymptomatic carriers often harbor the bacteria in their gallbladder or intestinal lining, leading to its continuous shedding and potential spread to others.
Step-by-step explanation:
The germ that causes Typhoid Fever can enter (and remain in) a carrier state because some individuals can become infected with S. typhi and carry the pathogen without showing any symptoms, making them asymptomatic carriers. These individuals may harbor the typhoid-causing bacteria within the gallbladder or intestinal epithelium. Asymptomatic carriers shed the bacteria continuously through their feces. This shedding can lead to the contamination of food or water if proper hygiene is not observed. When others consume contaminated substances, they can become infected with typhoid fever. This pathogen's ability to persist in the gallbladder or intestinal mucosa allows it to evade the immune system and be spread by carriers, as was the case with the infamous 'Typhoid Mary' in the early 1900s.
Furthermore, S. typhi can penetrate the intestinal mucosa and replicate within macrophages. Once transported to organs like the liver and gallbladder, it can lead to more severe systemic infections. In practice, careful hygiene, stringent sanitation measures, and vaccination are crucial in preventing the spread of typhoid fever, especially in parts of the world where the disease is common.