Option 1: Varicella zoster is not a bacterium that causes disease in the human body. Instead, it is a virus that causes chickenpox and shingles.

Option 2: Trypanosoma gambiense is also not a bacterium. It is a parasite that causes African trypanosomiasis, also known as sleeping sickness.

Option 3: Salmonella typhi is the correct answer. It is a bacterium that causes typhoid fever in humans. It is usually transmitted through contaminated food and water.

Option 4: Plasmodium falciparum is not a bacterium either. It is a parasite that causes malaria.

In conclusion, out of the given options, option 3, Salmonella typhi, is the bacterium that causes disease in the human body, specifically typhoid fever.