Which of the following correctly lists the steps in the chain of infection in the proper order?

• A. Infectious agent → Reservoir → Portal of exit → Mode of transmission → Portal of entry → Susceptible host
• B. Reservoir → Infectious agent → Portal of entry → Mode of transmission → Portal of exit → Susceptible host
• C. Portal of exit → Infectious agent → Reservoir → Susceptible host → Mode of transmission → Portal of entry
• D. Mode of transmission → Portal of entry → Reservoir → Infectious agent → Portal of exit → Susceptible host

Answer: (A)

Verified step by step guidance

1. Step 1: Understand that the chain of infection describes the sequence of events that allows an infectious disease to spread from one host to another.
2. Step 2: Identify the first link as the 'Infectious agent,' which is the pathogen (such as bacteria, virus, or fungus) that causes the disease.
3. Step 3: Recognize the 'Reservoir' as the place where the infectious agent normally lives and multiplies, such as humans, animals, or the environment.
4. Step 4: Determine the 'Portal of exit,' which is the path by which the infectious agent leaves the reservoir (e.g., respiratory tract, blood, or skin).
5. Step 5: Follow with the 'Mode of transmission,' which is how the infectious agent is transferred from the reservoir to a new host (e.g., direct contact, airborne, or vector-borne).
6. Step 6: Next is the 'Portal of entry,' the route through which the infectious agent enters the new host (e.g., mucous membranes, broken skin).
7. Step 7: Finally, the 'Susceptible host' is the individual who can become infected due to lack of immunity or other factors.
8. Step 8: Putting these steps in order gives the correct chain of infection: Infectious agent → Reservoir → Portal of exit → Mode of transmission → Portal of entry → Susceptible host.