**Core Concept**
Poliomyelitis is a highly infectious disease caused by the poliovirus, primarily affecting the nervous system. The transmission of poliomyelitis is mainly through the fecal-oral route, where the virus is shed in the feces of infected individuals and ingested by others.

**Why the Correct Answer is Right**
The correct answer is through fecal-oral transmission, where the poliovirus is ingested through contaminated food, water, or hands that have come into contact with feces containing the virus. This route of transmission is facilitated by poor hygiene and sanitation practices. The virus then enters the body through the gastrointestinal tract and multiplies in the gut, eventually invading the central nervous system and causing paralysis in some cases.

**Why Each Wrong Option is Incorrect**
**Option A:**
* This option is incorrect because while poliovirus can also be transmitted through direct contact with an infected person, fecal-oral transmission is the main route of transmission.

**Option B:**
* This option is incorrect because poliovirus is not transmitted through the air, unlike some other viral infections such as measles or influenza.

**Option C:**
* This option is incorrect because poliovirus is not transmitted through vectors such as mosquitoes or ticks, unlike some other diseases such as malaria or Lyme disease.

**Clinical Pearl / High-Yield Fact**
It's essential to note that poliomyelitis can also be transmitted through contaminated food and water, particularly in areas with poor sanitation and hygiene practices. This highlights the importance of proper hygiene and sanitation measures in preventing the spread of the disease.

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