Hydrophobia in Rabies
Hydrophobia is a pathognomonic clinical feature of rabies characterized by terror and violent spasms of the inspiratory muscles, larynx, and pharynx that are precipitated by attempts to drink water or even by the sight or sound of running water. 1
Clinical Mechanism and Presentation
Hydrophobia represents the hallmark symptom of furious (encephalitic) rabies, which accounts for approximately 80% of human rabies cases. 1 The phenomenon involves:
Violent spasms triggered by water-related stimuli: Patients experience terror and excitation with spasms of inspiratory muscles, larynx, and pharynx when attempting to drink or even when exposed to the sight or sound of running water 2
Exaggerated reflex response: This likely represents an exaggerated respiratory tract irritant reflex with associated arousal, potentiated by selective destruction of brain stem inhibitory systems 2
Progressive agitation: Patients become extremely agitated in the presence of stimuli such as loud noises, air currents, and the sight or sound of running water, particularly during the acute neurologic phase of the disease 3
Clinical Context and Associated Features
Hydrophobia occurs alongside other characteristic features of furious rabies:
Aerophobia: Present in 95.5% of cases, representing a similar reflex response to air currents 4
Intermittent behavioral changes: Episodes of agitation, hyperexcitability, and bizarre behavior alternating with periods of lucidity 1
Hypersalivation and autonomic dysfunction: Though hypersalivation was noted in only 6.7% of one large cohort, it remains a recognized feature 4, 5
Diagnostic Significance
Hydrophobia is pathognomonic for rabies, meaning its presence is virtually diagnostic of the disease. 1 This clinical sign:
Distinguishes rabies from other encephalitides: The specific pattern of water-triggered spasms is unique to rabies and helps differentiate it from conditions like tetanus, other viral encephalitides, or hysterical pseudo-hydrophobia 2
Defines the WHO case definition: The World Health Organization case definition for clinical rabies specifically requires the presence of hydrophobia 4
Clinical Management Implications
Once hydrophobia develops, the prognosis is universally poor:
No effective treatment exists: Rabies is not considered curable once clinical symptoms appear, with only 6 documented human survivors, and 5 of these had received vaccination before symptom onset 1
Sedation becomes necessary: When hydrophobia and associated agitation develop, adequate sedation in an appropriate medical facility becomes the primary focus of care 3, 1
Death typically follows rapidly: Patients with furious rabies typically die within 7 days of symptom onset 1
Critical Pitfall
The presence of hydrophobia indicates that the window for effective postexposure prophylaxis has closed. Initiation of rabies vaccination after onset of clinical symptoms in patients with confirmed rabies is not recommended and might be detrimental. 3 This underscores the absolute necessity of administering postexposure prophylaxis immediately after potential rabies exposure, before any clinical signs develop.