What are the clinical features of rabies?

Clinical Features of Rabies

Rabies presents as an acute encephalomyelitis that almost always progresses to coma or death within 10 days after the first symptom, manifesting in two distinct clinical forms: furious (encephalitic) rabies in 80% of cases and paralytic (dumb) rabies in 20% of cases. 1

Incubation Period

• The incubation period typically lasts 1-3 months but can range from days to over a year, with an average of one to two months. 2, 3
• During this stage, the patient remains asymptomatic despite viral replication and neural spread. 4

Prodromal Stage (Stage II)

• Non-specific constitutional symptoms develop, including fever, chills, headache, malaise, and myalgia. 1, 3
• Paresthesias or pain at the site of the original bite wound occur in many patients and are highly suggestive of rabies. 3, 5
• This prodromal period precedes the development of neurological symptoms by several days. 4, 3

Furious (Encephalitic) Rabies - 80% of Cases

Cardinal Features

• Hydrophobia is pathognomonic for rabies: terror and violent spasms of the inspiratory muscles, larynx, and pharynx precipitated by attempts to drink water or even by the sight or sound of running water. 1, 3
• Aerophobia: similar spasms triggered by air currents or drafts blown on the face. 6, 3
• These spasms represent an exaggerated respiratory tract irritant reflex with associated arousal, potentiated by selective destruction of brainstem inhibitory systems. 3

Neurological Manifestations

• Intermittent episodes of agitation, hyperexcitability, and bizarre behavior alternating with periods of lucidity. 1, 3
• Hallucinations, delirium, and maniacal behavior occur during acute episodes. 3, 5
• Disorientation progressing to stupor and coma. 1
• Focal neurological abnormalities are surprisingly uncommon despite severe encephalitis. 3

Autonomic Features

• Hypersalivation with inability to swallow secretions. 3, 5
• Tachycardia and cardiac arrhythmias. 3
• Hyperpyrexia (high fever). 3

Disease Progression

• Patients become extremely agitated in the presence of stimuli such as loud noises, air currents, and running water during the acute neurologic phase. 1, 6
• Paralysis and coma supervene after a few days. 3
• Death typically occurs within 7 days of symptom onset. 3, 5

Paralytic (Dumb) Rabies - 20% of Cases

Clinical Presentation

• Ascending flaccid paralysis resembling Guillain-Barré syndrome, starting from the bitten extremity. 1, 7
• Lower motor neuron weakness progressing cephalad. 5
• Sphincter involvement with urinary and fecal incontinence. 3
• Sensory disturbances may accompany the motor deficits. 3

Disease Course

• This form poses significant diagnostic challenges as it closely resembles Guillain-Barré syndrome, particularly when a clear exposure history is lacking. 7
• Death from respiratory and bulbar paralysis occurs after a longer illness than furious rabies (typically 10-14 days). 3
• In a minority of cases, hydrophobia may develop before terminal coma. 3

Brainstem Involvement

• The brainstem is preferentially involved in both clinical forms, though paradoxically there may be no overt clinical signs of brainstem dysfunction early in the disease. 7
• MRI may show nonenhancing focal lesions in basal ganglia, thalami, and brainstem. 1

Terminal Stage Complications

• Respiratory arrest and failure. 3, 5
• Pneumonitis and aspiration. 3
• Cardiac arrhythmias and interstitial myocarditis. 3
• Posterior pituitary disorders (diabetes insipidus, SIADH). 3
• Gastrointestinal bleeding. 3
• Multiple organ failure in aggressively managed patients. 5

Important Diagnostic Pitfalls

Differential Diagnosis of Furious Rabies

• Hysterical pseudohydrophobia (key distinction: true hydrophobia involves involuntary spasms, not voluntary avoidance). 3
• Tetanus (distinguished by sustained muscle rigidity rather than intermittent spasms). 3
• Other viral encephalitides. 3
• Delirium tremens and toxic encephalopathies. 3

Differential Diagnosis of Paralytic Rabies

• Guillain-Barré syndrome is the most common misdiagnosis. 7, 3
• Postvaccinal encephalomyelitis. 3
• Poliomyelitis and other causes of Landry-type ascending paralysis. 3

Prognosis

• 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. 8, 6
• Survival rarely exceeds 7 days in furious rabies without intensive support. 3
• When a definitive diagnosis is obtained, primary health considerations should focus on comfort care and adequate sedation in an appropriate medical facility. 1, 6