**Core Concept**
Hepatitis B virus (HBV) is a major cause of perinatal transmission, leading to chronic infection in the newborn. This transmission occurs when an infected mother passes the virus to her child during delivery.

**Why the Correct Answer is Right**
HBV has a unique ability to be transmitted vertically from mother to child, particularly during delivery. This transmission is mediated by the virus's ability to replicate in the liver and produce viral particles that can be shed in bodily fluids, including maternal blood and vaginal secretions. The newborn's immune system is not yet mature enough to mount an effective response to the virus, leading to a high risk of chronic infection. The transmission rate of HBV from mother to child can be as high as 90% if the mother is positive for the hepatitis B surface antigen (HBsAg) and not receiving antiviral prophylaxis.

**Why Each Wrong Option is Incorrect**
**Option A:** Hepatitis E virus (HEV) is primarily transmitted through the fecal-oral route, often through contaminated water or food, and is not typically associated with perinatal transmission.
**Option B:** Hepatitis C virus (HCV) can be transmitted vertically, but the transmission rate is significantly lower than HBV, around 5-6%.
**Option D:** Hepatitis A virus (HAV) is primarily transmitted through the fecal-oral route and is not typically associated with perinatal transmission.

**Clinical Pearl / High-Yield Fact**
The hepatitis B vaccine is highly effective in preventing perinatal transmission of HBV. All newborns should receive the first dose of the hepatitis B vaccine within 24 hours of birth, and the mother should receive post-exposure prophylaxis with hepatitis B immune globulin (HBIG) if she is HBsAg-positive.

**✓ Correct Answer: C. Hepatitis B virus**