**Core Concept**
The bubonic plague, caused by Yersinia pestis, is a zoonotic disease that primarily affects rodents and their fleas. In humans, it is transmitted through the bites of infected fleas or direct contact with infected animals. The term "dead-end host" refers to a host species that cannot maintain the disease cycle, meaning the pathogen cannot be transmitted to another host within that species.

**Why the Correct Answer is Right**
Humans are considered dead-end hosts for the bubonic plague because Yersinia pestis cannot complete its life cycle in humans. The bacterium can infect and multiply within the fleas that feed on infected rodents, but it cannot be transmitted from human to human or from human to flea. This is in contrast to other diseases, such as malaria, which can be transmitted between humans through the bite of an infected mosquito.

**Why Each Wrong Option is Incorrect**
**Option A:** Malaria is not transmitted between humans; it requires an intermediate host (the mosquito) to complete its life cycle. Humans are not considered dead-end hosts for malaria.
**Option B:** Typhoid is a disease that can be transmitted between humans through contaminated food and water. Humans are not dead-end hosts for typhoid.
**Option D:** Filaria, like other parasitic diseases, can be transmitted between humans through the bite of an infected mosquito or blackfly. Humans are not dead-end hosts for filaria.

**Clinical Pearl / High-Yield Fact**
The bubonic plague is often referred to as the "black death" due to its high mortality rate in the Middle Ages. To remember that humans are dead-end hosts for the bubonic plague, recall that the disease is primarily maintained in the rodent-flea cycle, and humans are simply an incidental host.

✓ Correct Answer: C. Bubonic plague