**Core Concept**
Hemorrhagic fevers are a group of viral infections characterized by severe bleeding, organ failure, and high mortality rates. These fevers are caused by distinct viral families, with the most common being the arenaviruses, flaviviruses, and bunyaviruses.

**Why the Correct Answer is Right**
The correct answer, **D. Crimean Congo virus**, is a member of the bunyavirus family, specifically the Nairovirus genus. Crimean Congo hemorrhagic fever (CCHF) is transmitted to humans through tick bites or contact with infected animals, causing symptoms such as fever, hemorrhaging, and multi-organ failure. The virus replicates in the host cells, leading to the production of viral particles and the activation of immune responses that can exacerbate the disease.

**Why Each Wrong Option is Incorrect**
* **Option A:** Lassa fever virus is caused by the arenavirus family, which is a different viral family responsible for hemorrhagic fevers. While it causes a similar disease, it is not the correct answer.
* **Option B:** Yellow fever virus is a flavivirus, primarily causing yellow fever in humans, which is distinct from hemorrhagic fevers.
* **Option C:** West Nile virus is also a flavivirus, primarily causing West Nile fever and encephalitis in humans, not hemorrhagic fever.
* **Option E:** Ross River virus is an alphavirus, causing Ross River fever, which is a different type of viral disease.

**Clinical Pearl / High-Yield Fact**
Arenaviruses, such as Lassa fever virus, require a specific animal host for replication and transmission to humans, while bunyaviruses, like Crimean Congo virus, can be transmitted through tick bites or contact with infected animals.

**Correct Answer: D. Crimean Congo virus**