hydrophobia

Hydrophobia occurs in the encephalitic (furious) form of rabies, a rhabdovirus infection transmitted via bites from infected animals (bats, raccoons, dogs in endemic areas). After peripheral entry, the virus undergoes retrograde axonal transport to the CNS, causing severe encephalitis with predilection for the brainstem and limbic system. Involvement of the medullary swallowing centers and pharyngeal muscles leads to painful, violent spasms of the throat and diaphragm upon attempting to drink water or even seeing/hearing water, hence 'hydrophobia.' This is often accompanied by aerophobia (fear of drafts of air), hypersalivation, agitation, hydrophobic spasms progressing to autonomic instability, and eventually paralysis, coma, and death. Diagnosis is largely clinical in endemic settings, supported by history of animal bite, direct fluorescent antibody testing on skin biopsy (nuchal), saliva PCR, or Negri bodies (eosinophilic cytoplasmic inclusions) on brain histopathology postmortem. Rabies is almost universally fatal once symptoms manifest; prevention via post-exposure prophylaxis (wound care, rabies immunoglobulin, and vaccine series) is critical before symptom onset. Hydrophobia is a key board-testable clinical clue for rabies among viral encephalitides, distinguishing it from HSV encephalitis (temporal lobe involvement, seizures) or arboviral encephalitides.