**Core Concept**
Hepatitis E virus (HEV) is a zoonotic pathogen primarily transmitted through the fecal-oral route, often associated with contaminated water and poor sanitation. This mode of transmission is particularly common in developing countries with inadequate waste management.

**Why the Correct Answer is Right**
The correct answer is related to the fecal-oral route of transmission, where the virus is shed in the feces of infected individuals, contaminating water sources or food. This mode of transmission is facilitated by poor hygiene and sanitation, allowing the virus to spread. The fact that the patient's family member also had the same symptoms, diagnosed as hepatitis E, suggests a possible household transmission through contaminated water or food.

**Why Each Wrong Option is Incorrect**
* **Option A:** Blood transfusion is not a common mode of transmission for hepatitis E virus, as it is not typically found in blood. This option is incorrect because HEV is not a bloodborne pathogen.
* **Option B:** Sexual transmission is not a recognized mode of transmission for hepatitis E virus. This option is incorrect because HEV is not a sexually transmitted infection.
* **Option C:** Vertical transmission (mother-to-child) is not a significant mode of transmission for hepatitis E virus. This option is incorrect because HEV is not typically transmitted from mother to child during pregnancy or childbirth.

**Clinical Pearl / High-Yield Fact**
Hepatitis E is often associated with contaminated water and poor sanitation, particularly in developing countries. The virus can also be transmitted through undercooked meat, especially pork and game meats.

**Correct Answer:** C.