**Core Concept**
Pediculus humanus, commonly known as the human louse, is a ectoparasite that infests human hair and feeds on human blood. As a vector, it plays a significant role in the transmission of various diseases.

**Why the Correct Answer is Right**
The primary mechanism of disease transmission by Pediculus humanus involves the ingestion of infected blood while feeding on human hosts. Once ingested, the pathogens are then transmitted to the louse, which can then excrete them in its feces. Humans become re-infected by scratching the affected area and introducing the contaminated feces into their skin. The most notable diseases transmitted by Pediculus humanus include epidemic typhus (caused by Rickettsia prowazekii), pediculosis (caused by various bacteria and fungi), and trench fever (caused by Bartonella quintana). The louse's ability to transmit these diseases is facilitated by its ability to feed on infected blood and its close association with humans.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately represent a disease transmitted by Pediculus humanus.
**Option B:** This option is incorrect because it is not a disease known to be transmitted by Pediculus humanus.
**Option C:** This option is incorrect because it is not a disease known to be transmitted by Pediculus humanus.

**Clinical Pearl / High-Yield Fact**
Pediculus humanus is a significant vector of disease transmission, particularly in areas with poor hygiene and overcrowding. Recognizing the importance of louse-borne diseases is crucial for public health interventions and disease prevention.

**Correct Answer: D. Epidemic typhus**