Incubation period of measles –
**Core Concept**
Measles is a highly contagious viral infection caused by the measles virus, characterized by a prodromal phase, followed by a rash, and then recovery. The incubation period of measles is the time between exposure to the virus and the onset of symptoms.
**Why the Correct Answer is Right**
The incubation period of measles typically ranges from 7 to 14 days, with an average of 10-12 days. During this period, the virus replicates in the respiratory tract and spreads to lymphoid tissues, leading to a viremic phase. The prodromal symptoms, such as fever, cough, and conjunctivitis, appear as a result of the immune response to the virus. The rash, which is a hallmark of measles, is a manifestation of the immune system's attempt to eliminate the virus.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the incubation period of measles is typically longer than 5 days.
**Option B:** Incorrect because the incubation period of measles is not shorter than 7 days.
**Option C:** Incorrect because the incubation period of measles is not longer than 3 weeks.
**Clinical Pearl / High-Yield Fact**
The incubation period of measles can be reduced by the administration of measles vaccine, which provides immunity against the virus. The vaccine is typically administered in two doses, with the second dose given at least 28 days after the first dose.
**Correct Answer: D. 10-14 days.**