## **Core Concept**
The question tests the understanding of the carrier state in various infectious diseases, particularly focusing on the types of diseases where healthy carriers are commonly found. Healthy carriers are individuals who harbor a pathogen but do not display symptoms of the disease and can transmit the pathogen to others.

## **Why the Correct Answer is Right**
Diphtheria is caused by *Corynebacterium diphtheriae*. Healthy carriers of diphtheria are a significant reservoir for the bacteria, and they play a crucial role in the spread of the disease. The carrier state is well-documented in diphtheria.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Typhoid - *Salmonella Typhi* can cause a carrier state in some individuals, notably the famous "Typhoid Mary," who was a healthy carrier.
* **Option B:** Hepatitis B - Hepatitis B virus (HBV) infection can lead to a chronic carrier state, and these carriers are a significant source of transmission.
* **Option C:** Measles - Measles is not typically associated with a healthy carrier state. The virus causes a clinically apparent illness, and there is no known asymptomatic carrier state for measles.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that for many viral infections like measles, the individual is infectious before the onset of rash and symptoms, but this does not equate to a "healthy carrier" state as seen with bacterial or chronic viral infections.

## **Correct Answer:** . Measles