**Core Concept**
Nasal myiasis is a rare condition characterized by the infestation of nasal passages with fly larvae (maggots). This condition typically occurs in individuals with compromised nasal mucosa, such as those with nasal trauma, surgery, or underlying chronic rhinitis.

**Why the Correct Answer is Right**
The presenting symptom of nasal myiasis is severe irritation with sneezing, which is due to the mechanical and chemical irritation caused by the fly larvae. As the maggots feed on the nasal secretions and tissues, they release enzymes that break down the tissue, leading to intense irritation and inflammation. This irritation triggers a strong allergic response, resulting in sneezing, which is often the initial symptom reported by patients. The nasal mucosa's response to the foreign invasion by the maggots leads to increased mucus production, nasal congestion, and sneezing.

**Why Each Wrong Option is Incorrect**
**Option B:** While maggots are indeed the causative agents of nasal myiasis, they are not typically the presenting symptom. Instead, patients may report symptoms such as irritation, sneezing, or nasal discharge before noticing the presence of maggots.

**Option C:** Nasal pain is a possible symptom of nasal myiasis but is not the most common presenting symptom. The intense irritation and inflammation caused by the maggots can lead to pain, but this is often secondary to the initial symptom of severe irritation with sneezing.

**Option D:** Impaired olfaction (loss of smell) can be a consequence of nasal myiasis due to the tissue damage and inflammation caused by the maggots. However, this is not the presenting symptom, and patients may initially report symptoms such as severe irritation with sneezing.

**Clinical Pearl / High-Yield Fact**
Nasal myiasis is a medical emergency that requires prompt treatment. Early recognition and removal of the maggots are essential to prevent further tissue damage and potential complications, such as secondary infections or nasal septal perforation.

**✓ Correct Answer: A. Severe irritation with sneezing**