Typhoid fever, a water-borne disease, is caused by:

Concept

Infectious diseases are classified by the biological type of their causative agent, such as a virus, bacterium, protozoan, or helminth.

Typhoid is acquired mainly through the faecal–oral route when food or water is contaminated by an infected person or carrier.

Application

1. Identify the named disease: typhoid fever.

2. Recall its causative organism: Salmonella enterica serovar Typhi, commonly called Salmonella Typhi.

3. Classify that organism: Salmonella Typhi is a bacterium, so the required agent category is bacteria.

Contrast

• Viruses are acellular infectious agents; waterborne viral illnesses include hepatitis A and norovirus infection.

• Protozoans are single-celled eukaryotic parasites; Giardia and Entamoeba can spread through contaminated water.

• Helminths are multicellular parasitic worms; their diseases have different causative organisms from Salmonella Typhi.

Result

Therefore, typhoid fever is caused by bacteria, specifically Salmonella Typhi.