Which of the following is NOT a normal portal of exit for an infectious disease?

• A. Cerebrospinal fluid
• B. Blood
• C. Saliva
• D. Urine

Answer: (A)

Verified step by step guidance

1. Understand the concept of 'portal of exit' in infectious diseases: it refers to the route through which a pathogen leaves the host to spread to others.
2. Identify common normal portals of exit, which typically include bodily fluids and secretions such as blood, saliva, urine, feces, respiratory droplets, and skin lesions.
3. Evaluate each option given: blood, saliva, and urine are all common fluids through which pathogens can exit the body and spread infection.
4. Consider cerebrospinal fluid (CSF): it is normally contained within the central nervous system and is not typically exposed or released outside the body under normal conditions, so it is not a usual portal of exit.
5. Conclude that cerebrospinal fluid is NOT a normal portal of exit for infectious diseases because it does not normally leave the body to transmit infection.