Rabies is a fatal viral encephalitis which accounts for 30,000 to 70,000 human deaths worldwide each year. It is transmitted primarily through bites or scratches from infected animals, but infection through inhalation and organ transplantation has also been described. Rabies progresses through five stages, each with characteristic physical symptoms.
Incubation
Rabies is associated with a relatively long incubation period (months to years, average one to three months) during which the affected individual is asymptomatic. Some individuals describe a transient tingling sensation at the exposure site within a few days of infection, but this is not universal.
Prodrome
Physical symptoms of rabies appear when the virus reaches the dorsal root gangia and enters the central nervous system (CNS). Persistent pain, tingling, or itching at the exposure site is the most common initial complaint. On or around this time, patients typically describe the onset of non-specific, flu-like symptoms including fever, chills, fatigue, muscle aches, headache and irritability which may last for a few days or up to two weeks.
Acute Neurologic Rabies
The acute neurologic phase of rabies is characterized by rapid reproduction of the virus within the CNS and dissemination to other organs and tissues, including the saliva. Physical symptoms follow one of two patterns: encephalitic or paralytic.
Encephalitic or "furious" rabies accounts for 80 percent of cases. It is characterized by nervousness, hyperactivity, hallucinations, excessive salivation, hydrophobia (fear of water) and aerophobia (fear of air). Muscle spasms in the small muscles of the pharynx and larynx make swallowing and breathing extremely painful, accounting for the latter symptoms. Spasms may be triggered by the sight or sound of water. "Foaming at the mouth" is the combined result of hypersalivation and difficulty swallowing. Death usually ensues within five to seven days.
Paralytic or "dumb" rabies has been linked to a species of vampire bats found outside the United States. Individuals afflicted with this less common variant typically present with loss of muscle tone and paralysis in the limb initially exposed to the virus. Paralysis is progressive, eventually affecting all of the limbs (quadriparesis) and may be symmetric, first affecting a single side of the body, or asymmetric. Individuals become incontinent of feces and urine. In countries where access to mechanical ventilation and intensive care unit services is limited, paralysis of the diaphragm results in death due to respiratory failure. The course of "dumb" rabies is typically slower, with death occurring within a few weeks.
Coma & Death
Coma and death are the final common endpoint of rabies. In addition to coma, rabies causes profound multisystem organ failure, including respiratory failure, kidney failure, and heart failure. 30 to 60 percent of patients vomit blood during the last few hours of life. Cardiac arrhythmia occurs in virtually 100 percent of cases, with the final cause of death often related to cardiac and circulatory failure.
