**Core Concept**
Hepatitis E is a viral liver infection primarily caused by the hepatitis E virus (HEV), which spreads through fecal-oral transmission. This involves the ingestion of contaminated food or water, leading to the entry of the virus into the host's gastrointestinal tract.

**Why the Correct Answer is Right**
The most common route of spread in hepatitis E is through the fecal-oral transmission of the virus. This typically occurs when individuals consume food or water contaminated with feces containing the HEV virus. The virus then enters the host's gastrointestinal tract and replicates, leading to the development of symptoms such as jaundice, fatigue, and abdominal pain. The contaminated food or water can be sourced from various places, including undercooked pork, wild boar, or other infected animals.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not correct as hepatitis E is not primarily spread through sexual transmission.
**Option B:** Although hepatitis E can be transmitted through blood transfusion, this is not the most common route of spread.
**Option C:** This option is incorrect as hepatitis E is not primarily spread through parenteral transmission, such as through IV drug use.

**Clinical Pearl / High-Yield Fact**
It is essential to note that hepatitis E is a self-limiting disease, and most individuals recover without specific treatment. However, pregnant women, especially in the third trimester, are at an increased risk of developing severe hepatitis E, which can be fatal in some cases.

**Correct Answer: D. Fecal-oral transmission.