Usually 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.
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 are progressive.
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.
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).
About 50% of affected patients exhibit hydrophobia (literally, “fear of water”), during which forceful, painful pharyngeal muscle spasms expel liquids from the mouth and cause dehydration, and possibly apnea, cyanosis, and death. Difficulty swallowing causes frothy saliva to drool from the patient’s mouth.
Eventually, even the sight, mention, or thought of water causes uncontrollable pharyngeal muscle spasms and excessive salivation. Between episodes of excitation and hydrophobia, the patient commonly is cooperative and lucid.
After about 3 days, excitation and hydrophobia subside and the progressively paralytic, terminal phase of this illness begins. The patient experiences gradual, generalized, flaccid paralysis that ultimately leads to peripheral vascular collapse, coma, and death.
Because rabies is fatal unless treated promptly, always suspect rabies in any person who suffers an unprovoked animal bite, until you can prove otherwise.
Virus isolation from the patient’s saliva or throat and examination of his blood for fluorescent rabies antibody (FRA) provide the most evidence for a definitive diagnosis. Other results typically include an elevated white blood cell count, with increased polymorphonuclear and large mononuclear cells, and elevated urinary glucose, acetone, and protein levels.
Confinement of the suspected animal for 10 days of observation by a veterinarian may also provide evidence to support this diagnosis. If the animal appears rabid, it should be killed and its brain tissue tested for FRA and Negri bodies (oval or round masses that conclusively confirm rabies).
The patient requires wound treatment and immunization as soon as possible after exposure.
Thoroughly wash all bite wounds and scratches with soap and water. (See First aid in animal bites.)
Check the patient’s immunization status, and administer tetanus-diphtheria prophylaxis, if needed. Take measures to control bacterial infection. If the wound requires suturing, special treatment and suturing techniques must be used to allow proper wound drainage.
CLINICAL TIP: If the wound is sutured, antiserum may be infiltrated locally.
After rabies exposure, a patient who hasn’t been previously immunized must receive passive immunization with rabies immune globulin and active immunization with human diploid cell vaccine as soon as possible. If the patient previously received the vaccine and has an adequate rabies antibody titer, he doesn’t need immune globulin immunization, just a vaccine booster.
❑ When injecting the rabies vaccine, rotate injection sites on the upper arm or thigh. Watch for and treat symptoms of redness, itching, pain, and tenderness at the injection site.
❑ Cooperate with public health authorities to determine the vaccination status of the animal. If the animal is proven rabid, help identify others at risk.
❑ If rabies develops, provide aggressive supportive care (even after onset of coma) to make probable death less agonizing.
❑ Continuously monitor cardiac and pulmonary function.
❑ Isolate the patient. Wear a gown, gloves, and protection for the eyes and mouth when handling saliva and articles contaminated with saliva. Take precautions to avoid being bitten by the patient during the excitation phase.
❑ Keep the room dark and quiet.
❑ Provide psychological support to the patient and family to help them cope with the patient’s symptoms and probable death.
❑ To help prevent this dreaded disease, stress the need for vaccination of household pets that may be exposed to rabid wild animals. Tell pet owners that if a wild animal bites a pet, they should seek veterinary assistance immediately. Warn people to avoid touching wild animals, especially if they appear ill or overly docile (a possible sign of rabies).
❑ Recommend prophylactic rabies vaccine to high-risk people, such as farm workers, forest rangers, spelunkers (cave explorers), and veterinarians.
Review other book chapters online related to Rabies:
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Handbook of Diseases Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2003 ISBN: 1-58255-266-5 
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