**Core Concept**
Poliovirus is a highly infectious agent that causes poliomyelitis, primarily affecting the gastrointestinal tract and the nervous system. The virus enters the body through a specific route, which is crucial for its transmission and pathogenesis.

**Why the Correct Answer is Right**
The portal of entry for poliovirus is mainly through the oral-fecal route, where the virus is ingested through contaminated food or water. Once ingested, the virus replicates in the enteric mucosa, particularly in the small intestine, where it attaches to the intestinal epithelial cells via its attachment proteins. This attachment is facilitated by the presence of the poliovirus receptor, CD155, which is expressed on the surface of these cells. The virus then undergoes replication and spreads to the regional lymph nodes, from where it enters the bloodstream and eventually reaches the central nervous system.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because while poliovirus can also enter the body through other routes, such as through cuts or abrasions on the skin, the primary portal of entry is through the oral-fecal route.
* **Option B:** This option is incorrect because while the respiratory tract can be a site of poliovirus replication, it is not the primary portal of entry for the virus.
* **Option C:** This option is incorrect because while poliovirus can attach to and replicate in various cell types, the primary attachment site is the enteric mucosa of the small intestine.

**Clinical Pearl / High-Yield Fact**
The oral-fecal route of transmission for poliovirus highlights the importance of proper hand hygiene and sanitation in preventing the spread of the disease.

**Correct Answer: D. Oral-fecal route.**