Rabies
LIFE-THREATENING DISORDERUsually transmitted by an animal bite, rabies (hydrophobia) is an acute central nervous system (CNS) infection caused by a ribonucleic acid virus.
The incubation period ranges from 10 days to 7 years, with an average of 3 to 7 weeks. In the United States, dog vaccinations have reduced rabies transmission to humans. Wild animals—such as raccoons, skunks, foxes, and bats—account for 70% of rabies cases.
If symptoms occur, rabies is almost always fatal. Treatment soon after a bite, however, may prevent fatal CNS invasion.
Causes
Generally, the rabies virus is transmitted to a human through the bite of an infected animal that introduces the virus through the skin or mucous membrane. The virus begins to replicate in the striated muscle cells at the bite site.
It next spreads up the nerve to the CNS and replicates in the brain. Finally, it moves through the nerves into other tissues, including the salivary glands. Occasionally, airborne droplets and infected tissue transplants can transmit the virus.
Signs and symptoms
Signs and symptoms are progressive.
Local and prodromal symptoms
Typically, after an incubation period of 1 to 3 months, rabies produces local or radiating pain or burning, a sensation of cold, pruritus, and tingling at the bite site. It also produces prodromal signs and symptoms, such as a slight fever (100° to 102° F [37.8° to 38.9° C]), malaise, headache, anorexia, nausea, sore throat, and persistent loose cough.
After this, the patient begins to show nervousness, anxiety, irritability, hyperesthesia, photophobia, sensitivity to loud noises, pupillary dilation, tachycardia, shallow respirations, and excessive salivation, lacrimation, and perspiration.
Excitation and hydrophobia
Between 2 and 10 days after onset of prodromal symptoms, a phase of excitation begins. It’s characterized by agitation, marked restlessness, anxiety, apprehension, and cranial nerve dysfunction that causes ocular palsies, strabismus, asymmetrical pupillary dilation or constriction, absence of corneal reflexes, weakness of facial muscles, and hoarseness. Severe systemic signs and symptoms include tachycardia or bradycardia, cyclic respirations, urine retention, and a temperature of about 103° F (39.4° C).
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