Symptoms of Human Rabies Infection
Human rabies presents in two distinct clinical forms: furious (encephalitic) rabies in 80% of cases, characterized by hydrophobia and hyperexcitability, and paralytic (dumb) rabies in 20% of cases, characterized by ascending flaccid paralysis. 1, 2
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 1
- During this stage, no symptoms are present 3
Prodromal Stage (Stage II)
- Constitutional symptoms including fever, malaise, and headache 3
- Pain, paresthesias, or pruritus at the site of the original wound 3
- Nonspecific symptoms that may last 2-10 days 3
Furious (Encephalitic) Rabies - 80% of Cases
Pathognomonic 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
- Aerophobia: similar spasms triggered by air currents or drafts 2
Neurological Manifestations
- Intermittent episodes of agitation, hyperexcitability, and bizarre behavior alternating with periods of lucidity 1
- Episodes of generalized arousal or hyperexcitability 2
- Extreme agitation in the presence of stimuli such as loud noises, air currents, and running water 1
- Disorientation progressing to stupor and coma 1
Paralytic (Dumb) Rabies - 20% of Cases
- Ascending flaccid paralysis resembling Guillain-Barré syndrome, starting from the bitten extremity 1, 4
- Progressive lower motor neuron weakness 2
- This form poses particular diagnostic challenges as it closely mimics Guillain-Barré syndrome 4
Terminal Stage
- Progression to coma (Stage IV) 3
- Death typically occurs within 7 days of symptom onset 1
- Death almost always occurs within 10 days after the first symptom 1
Critical Clinical Pitfalls
- Rabies may present without hydrophobia or hypersalivation, particularly in atypical cases or after postexposure prophylaxis, making diagnosis more difficult 5
- The paralytic form is frequently misdiagnosed as Guillain-Barré syndrome, especially when a clear history of animal bite is absent 4
- Cardinal signs may be lacking when a patient is comatose, further complicating diagnosis 4
- Once clinical symptoms appear, rabies is not considered curable, with only 6 documented human survivors, and 5 of these had received vaccination before symptom onset 1