Usually transmitted by an animal bite, rabies (hydrophobia) is an acute central nervous system (CNS) infection caused by a ribonucleic acid virus.
If the bite is on the face, the risk of developing rabies is about 60%; on the upper extremities, 15% to 40%; and on the lower extremities, about 10%. In the United States, dog vaccinations have reduced rabies transmission to humans. Wild animals, such as 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.
Rabies is caused by the rod- or bullet-shaped Rhabdoviridae. People are infected with this virus when bitten by an infected animal. The virus spreads from the saliva of the animal, along the nerves, to the spinal cord and brain (the central nervous system). It multiplies in the central nervous system, and then travels down nerves to the salivary glands and into the saliva. While most cases of rabies are transmitted by a bite from an infected animal, it can also be transmitted if the infected animal licks you around an open wound, or mucous membranes such as the eyes, nose, or mouth. It is also believed that the virus can be gotten by breathing the infected air in a bat-infested cave. Because of the widespread use of the rabies vaccine for pets in the United States, today most cases of rabies are transmitted by wild animals such as bats, foxes, raccoons, skunks, coyotes, and wolves.
Signs and symptoms
Clinical features 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 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
About 2 to 10 days after onset of prodromal symptoms, a phase of excitation begins. It's characterized by agitation, marked restlessness, anxiety and 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 symptoms include tachycardia or brachycardia, cyclic respirations, urinary 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) are considered the tests that provide the most 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 also helps 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.
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.
If there is any risk of rabies, you will be given a preventative vaccine.
There is no known cure for symptomatic rabies, but it can be prevented by vaccination , both in humans and other animals.
Being safe around animals, even your own pets, can help reduce the risk of animal bites. Some general guidelines for avoiding animal bites and rabies include the following:
Teaching your child about animal safety may also help to prevent animal bites. Some things to remember include the following:
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