**Question:** Rabies virus

**Core Concept:** Rabies virus is a neurotropic virus that causes a fatal encephalitis in mammals. It belongs to the Rhabdoviridae family, Lyssavirus genus. The virus primarily affects the central nervous system (CNS) and leads to a characteristic progressive neurological disease, named rabies.

**Why the Correct Answer is Right:** Rabies virus (Rabies lyssavirus) is a zoonotic virus transmitted through the saliva of infected animals, particularly dogs, bats, and raccoons. Once the virus enters the body, it primarily targets the central nervous system (CNS) and follows a characteristic clinical course. The primary mode of transmission is through the bite of an infected animal, which allows the virus to enter the body and spread to the brain.

**Why Each Wrong Option is Incorrect:**

A. **Incorrect**: Rabies is not known to affect the respiratory system directly. While the virus may cause some respiratory symptoms initially, it primarily affects the CNS, leading to the characteristic rabies syndrome.

B. **Incorrect**: Rabies virus does not primarily target the skin or blood vessels. Instead, it invades the CNS, causing neurological symptoms and the characteristic disease progression.

C. **Incorrect**: Rabies is not known to affect the gastrointestinal tract as its primary target. The virus primarily affects the CNS, leading to the distinctive neurological symptoms associated with rabies.

D. **Incorrect**: Rabies virus does not primarily target the cardiovascular system. The virus primarily affects the CNS, causing neurological symptoms and the characteristic disease progression.

**Correct Answer:**

**Answer:** C. Rabies virus affects the central nervous system (CNS).

**Explanation:** Rabies virus is a neurotropic virus that primarily targets the central nervous system (CNS) of mammals, leading to the characteristic neurological symptoms associated with the disease. Once the virus enters the body through an infected animal bite, it follows a specific clinical course, with symptoms typically starting in the salivary glands and then spreading to the brain and spinal cord. This is why the correct answer is C, as it highlights the primary target of the rabies virus, which is the central nervous system. The other options (A, B, and D) are incorrect because rabies virus primarily affects the CNS, causing the disease and its distinct neurological symptoms, rather than the respiratory, skin, gastrointestinal, or cardiovascular systems.