Transmission of hepatitis A virus occurs -a) One week before and one week after onset of symptomb) 2 weeks before onset of symptomsc) 2 weeks after onset of symptomsd) 1 week after onset of symptoms

**Core Concept**
Hepatitis A virus (HAV) is primarily transmitted through the fecal-oral route, where the virus is shed in the stool of infected individuals and ingested by others, often through contaminated food or water. The virus has a relatively short incubation period, during which the individual may not be symptomatic but can still infect others.

**Why the Correct Answer is Right**
The correct answer is **B) 2 weeks before onset of symptoms**. This is because HAV has an incubation period of approximately 14-28 days, during which the individual is asymptomatic but can still shed the virus in their stool. The virus is most contagious during the 2 weeks preceding the onset of symptoms, making this period the most likely time for transmission to occur.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the period of 1 week before and 1 week after the onset of symptoms is too narrow to account for the entire incubation period of HAV.
* **Option C:** This option is incorrect because the virus is most contagious before the onset of symptoms, not after.
* **Option D:** This option is incorrect because the virus is shed in the stool for a longer period before the onset of symptoms, making it more likely to be transmitted during this time.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that HAV is primarily transmitted through the fecal-oral route, and the virus is most contagious during the 2 weeks preceding the onset of symptoms. This knowledge can help clinicians and public health officials develop targeted interventions to prevent the spread of the virus.

**Correct Answer: B. 2 weeks before onset of symptoms.**