**Core Concept**
Poliomyelitis, caused by the poliovirus, is a highly infectious disease that can lead to severe consequences, including death. The virus primarily affects the motor neurons in the spinal cord, resulting in muscle weakness and paralysis. In severe cases, respiratory failure can occur due to involvement of the muscles that control breathing.

**Why the Correct Answer is Right**
Death in poliomyelitis is usually due to respiratory failure, which can occur as a result of paralysis of the diaphragm and accessory respiratory muscles. This can lead to hypoxia and eventually cardiac arrest. The virus's ability to invade and destroy motor neurons in the spinal cord is the primary mechanism leading to respiratory failure.

**Why Each Wrong Option is Incorrect**
**Option A:** While respiratory failure is a common cause of death in poliomyelitis, other options listed are not the primary cause of death. Therefore, this option is incorrect.
**Option B:** Cardiovascular collapse is not a direct result of poliovirus infection, making this option incorrect.
**Option C:** While poliomyelitis can lead to paralysis, this is not the direct cause of death, making this option incorrect.

**Clinical Pearl / High-Yield Fact**
In poliomyelitis, paralysis of the diaphragm and accessory respiratory muscles can lead to respiratory failure, which is a medical emergency requiring prompt respiratory support.

**Correct Answer: A. Respiratory failure.**