Clinical Features of Rabies

Common signs and symptoms

After a rabies exposure in the absence of post-exposure prophylaxis, the virus must travel to the brain before it can cause symptoms. Therefore, the incubation period may last for weeks to months based on:

• Location of the exposure site (proximity to the brain)
• Severity of exposure
• Patient age, as younger children may have shortened incubation periods
• Rabies vaccination status

The first symptoms of human rabies may last for several days:

• Prodrome including weakness, discomfort, fever, or headache
• Discomfort, prickling, or an itching sensation at the site of the bite

Usually, severe disease causes brain dysfunction within two weeks of the first symptoms. Signs of dysfunction may include one or more of the following:

• Anxiety
• Insomnia
• Confusion
• Agitation
• Delirium
• Hallucinations
• Hydrophobia (fear of water)
• Hypersalivation
• Seizures

Rabies causes encephalitis in infected patients. While all patients with encephalitis may not have rabies, all patients with rabies present with encephalitis. Rabies is rare in the U.S., and other more common causes of encephalitis should be ruled out before pursuing rabies testing unless a recent suspect rabies exposure occurred.

Clinical assessment

Rabies presents as a severe, acute illness with hospitalization required within days to several weeks of initial symptom onset.

Positive indicators for rabies

• Nonspecific prodrome phase prior to onset of neurologic signs
• Neurologic signs consistent with encephalitis or myelitis
• Dysphagia, hydrophobia, paresis, and autonomic instability
• Progression of neurologic signs
• Negative test results for other etiologies of encephalitis
• Herpesvirus, arboviruses, enteroviruses, autoimmune disorders, certain cancers

Negative indicators for rabies

• Improvement or no change in neurologic status after several weeks of illness
• Illness persisting longer than four weeks
• Diagnosis of an alternative cause for encephalitis