Rabies Clinical Presentation

Updated: Sep 11, 2017
  • Author: Sandra G Gompf, MD, FACP, FIDSA; Chief Editor: Michael Stuart Bronze, MD  more...
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Presentation

History

Identify the following in any suspected case of rabies virus exposure:

  • The nature of the interaction with the animal (Recall that "provocation" is not an indication of rabies risk, since humans may not understand what is provocative to a wild animal.)
  • Strange animal behavior (eg, nocturnal animal out during the daytime)
  • Vaccination status of the animal for rabies [8]
  • Availability of the animal for testing

Incubation period

The infected individual remains asymptomatic during this period. The average duration of incubation is 20-90 days. Rarely, incubation has been reported up to 7-19 years. In more than 90% of cases, incubation is less than 1 year. Patients may not recall exposure because of the prolonged incubation period.

The incubation period is less than 50 days if the patient is bitten on the head or neck or if a heavy inoculum is transferred through multiple bites, deep wounds, or large wounds. A person with a scratch on the hand may take longer to develop symptoms of rabies than a person who receives a bite to the head.

The rabies virus is segregated from the immune system during this period, and no antibody response is observed.

Prodromal period

The virus enters the CNS. The duration of this period is 2-10 days. Nonspecific symptoms and signs develop. Paresthesia, pain, or intense itching at the inoculation site is pathognomonic for rabies and occurs in 50% of cases during this phase; this may be the individual’s only presenting sign. Symptoms may include the following:

  • Malaise
  • Anorexia
  • Headaches
  • Fever
  • Chills
  • Pharyngitis
  • Nausea
  • Emesis
  • Diarrhea
  • Anxiety
  • Agitation
  • Insomnia
  • Depression

Acute neurologic period

This period is associated with objective signs of developing CNS disease. The duration is 2-7 days. Symptoms include muscle fasciculations, priapism, and focal or generalized convulsions. Patients may die immediately or may progress to paralysis, which may be present only in the bitten limb at first but usually becomes diffuse.

The form of rabies known as furious rabies may develop during this period. Patients develop agitation, hyperactivity, restlessness, thrashing, biting, confusion, or hallucinations. After several hours to days, this becomes episodic and interspersed with calm, cooperative, lucid periods. Furious episodes last less than 5 minutes. Episodes may be triggered by visual, auditory, or tactile stimuli or may be spontaneous. Seizures may occur. This phase may end in cardiorespiratory arrest or may progress to paralysis.

Another form of rabies, paralytic rabies, is also known as dumb rabies or apathetic rabies, because the patient is relatively quiet compared with a person with the furious form. Twenty percent of patients do not develop the furious form. Paralysis occurs from the outset, and fever and headache are prominent.

Coma

This begins within 10 days of onset, and the duration varies. Without intensive supportive care, respiratory depression, arrest, and death occur shortly after coma.

Next:

Physical Examination

Neurologic period

With furious rabies, patients present with episodic delirium, psychosis, restlessness, thrashing, muscular fasciculations, seizures, and aphasia. Hydrophobia and aerophobia are pathognomonic for rabies and occur in 50% of patients. Attempting to drink or having air blown in the face produces severe laryngeal or diaphragmatic spasms and a sensation of asphyxia. This may be related to a violent response of the airway irritant mechanisms. Even the suggestion of drinking may induce hydrophobic spasm.

Autonomic instability is observed with furious rabies, with symptoms that include the following:

  • Fever
  • Tachycardia
  • Hypertension
  • Hyperventilation
  • Anisocoria, fixed pupillary dilation (“blown pupil”), optic neuritis (may falsely suggest brain death)
  • Facial palsy
  • Mydriasis
  • Lacrimation
  • Excessive salivation
  • Perspiration
  • Postural hypotension

In patients with paralytic rabies, fever and nuchal rigidity may occur. Paralysis is symmetrical and may be either generalized or ascending and may be mistaken for Guillain-Barré syndrome. The sensory system is usually spared. Calm clarity gradually progresses to delirium, stupor, and then coma.

Coma

Respiratory failure occurs within 1 week of neurologic symptoms. Hypoventilation and metabolic acidosis predominate. Acute respiratory distress syndrome is common. Wide variations in blood pressure, cardiac arrhythmias, and hypothermia ensue. Bradycardia and cardiac arrest occur. With intensive support, life may be extended for 3 or 4 months; however, death is usually the outcome.

Death

It is important to determine brain death by brain biopsy or absence of cerebral arterial flow, because some of the neurologic signs may falsely suggest brain death (see above).

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