**Core Concept**
Vectors play a crucial role in the transmission of infectious diseases. They can transmit pathogens through various mechanisms, including mechanical transmission, biological transmission, and viral transmission. Understanding the methods by which vectors transmit infection is essential for disease prevention and control.

**Why the Correct Answer is Right**
Vectors primarily transmit infection through mechanical means, where the pathogen is carried on the vector's body or mouthparts. Regurgitation and rubbing of infected faeces are examples of mechanical transmission, as the pathogen is directly deposited onto a susceptible host. Contamination with body fluids can also occur through mechanical transmission. In contrast, ingestion is not a primary method of transmission for vectors, as they do not typically ingest pathogens and then transmit them to hosts.

**Why Each Wrong Option is Incorrect**
**Option B:** Regurgitation is indeed a method of transmission for vectors, particularly for pathogens like Plasmodium, which is transmitted through the regurgitation of the Anopheles mosquito.

**Option C:** Rubbing of infected faeces is also a valid method of transmission for vectors, as seen in the case of certain species of flies that transmit pathogens through their faecal-oral route.

**Option D:** Contamination with body fluids can occur through mechanical transmission, as vectors may come into contact with infected body fluids and then transfer them to a susceptible host.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the mode of transmission for a particular disease is often specific to the vector involved. Understanding the vector's behavior, habitat, and feeding habits can help identify the most likely method of transmission.

✓ Correct Answer: A. Ingestion