- Hydrophobia is a characteristic symptom of rabies caused by painful spasms of the pharyngeal muscles triggered by attempts to drink or even the sight of water.
- This symptom reflects neurological involvement of the brainstem and is highly suggestive of rabies infection.
- It is a distinctive and classical clinical feature that helps differentiate rabies from other causes of encephalitis.
- Hydrophobia arises due to irritation and inflammation of the cranial nerves and respiratory tract muscles, leading to fear and avoidance of water.
- Other options like ptosis, photophobia, and polyarthritis are not typical features of rabies.

Reference: Davidson’s Principles and Practice of Medicine, 24th Edition, Chapter: Diseases of the Nervous System, Page 649.