**Core Concept**
Acute appendicitis is a clinical condition characterized by inflammation of the vermiform appendix, often resulting from luminal obstruction. The earliest symptom is typically related to peritoneal irritation due to the release of inflammatory mediators.

**Why the Correct Answer is Right**
The earliest symptom of acute appendicitis is often **non-specific abdominal pain**. This type of pain is usually diffuse and can be localized to the periumbilical region, which is a result of the initial release of histamine and bradykinin, leading to vasodilation and increased vascular permeability. As the inflammation progresses, the pain typically migrates to the right lower quadrant (RLQ) due to the referred pain from the parietal peritoneum.

**Why Each Wrong Option is Incorrect**
* **Option A:** Nausea and vomiting are common symptoms of acute appendicitis but are not the earliest symptom. They usually occur after the onset of abdominal pain.
* **Option B:** Loss of appetite is not a specific or early symptom of acute appendicitis. It can be seen in various gastrointestinal disorders.
* **Option C:** Fever is a late symptom of acute appendicitis, typically occurring after the onset of abdominal pain and localized tenderness.

**Clinical Pearl / High-Yield Fact**
In cases of suspected acute appendicitis, it is essential to note that the pain often starts as non-specific and later localizes to the RLQ, a phenomenon known as **Rovsing's sign**. This sign is a classic clinical correlation in diagnosing appendicitis.

**Correct Answer: C. Fever is a late symptom of acute appendicitis, typically occurring after the onset of abdominal pain and localized tenderness.