A 12-year-old boy develops fever, accompanied by occasional headaches, malaise, fatigue, and nausea a month after being bitten by a dog. One day later, he experiences episodes of rigidity, hallucinations, breath-holding, and difficulty swallowing because of uncontrollable oral secretions. Dr. Louis Pasteur is consulted. He writes: “The death of this child appearing to be inevitable, I decided, not without lively and sore anxiety, as may well be believed, to try ……. the method which I had found constantly successful with dogs. Consequently, 60 hours after the bites was inoculated under a fold of skin with half a syringeful of the spinal cord of a rabbit. In the following days, fresh inoculations were made. I thus made 13 inoculations.” The boy survives. Which of the following histologic findings in the brain of the dog is most likely to be present?

**Core Concept**
The question describes a scenario of rabies transmission and treatment using the Pasteur vaccine. The correct answer is related to the histopathological changes observed in the brain of a dog infected with rabies.

**Why the Correct Answer is Right**
The Pasteur vaccine was developed using the spinal cord of infected rabbits, which contained the virus responsible for rabies. In dogs, the rabies virus causes severe inflammation of the brain, leading to the formation of Negri bodies, which are characteristic histopathological changes. These bodies are composed of viral particles surrounded by a halo of degenerating host cell cytoplasm. The presence of Negri bodies is a diagnostic feature of rabies infection.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not describe a specific histopathological feature associated with rabies infection.
* **Option B:** This option is incorrect because it is not related to the histopathological changes observed in the brain of a dog infected with rabies.
* **Option C:** This option is incorrect because it is not a characteristic histopathological feature of rabies infection.
* **Option D:** This option is incorrect because it is not specific to the histopathological changes observed in the brain of a dog infected with rabies.

**Clinical Pearl / High-Yield Fact**
Negri bodies are a key diagnostic feature of rabies infection. They are formed when the rabies virus infects the neurons of the brain, leading to the formation of viral particles surrounded by degenerating host cell cytoplasm.

**Correct Answer:** **C. Negri bodies**

✓ Correct Answer: B. Negri bodies