CHAPTER 17
Rabies
Rabies is an acute fatal viral illness of the central nervous system (CNS). The
word rabies is derived from the Latin verb to rage, which suggests the appearance
of the rabid patient. It can affect all mammals and is transmitted between them by
infected secretions, most often by bite. It was first recognized more than 3000
years ago and has been the most feared of infectious diseases. It is said that
Aristotle recognized that rabies could be spread by a rabid dog.
I. VIROLOGY
1. Enveloped RNA virus is bullet-shaped
2. Knob-like envelope glycoproteins elicit neutralizing and hemagglutination
antibodies
3. Strains from different sources are antigenically heterogeneous
4. Negative sense RNA virus replicates in the cytoplasm
5.
G protein containing lipoprotein envelope acquired from plasma membrane
II.RABIES
A. EPIDEMIOLOGY
1. Urban form is associated with unimmunized dogs or cats
2. Sylvatic form occurs in wild skunks, foxes, wolves, raccoons, and bats but not
rodents or rabbits disease
3. Occasional case has resulted from aerosol exposure eg, bat caves
4. Human infection is blind-ended, and does not contribute to maintenance or
transmission
B. PATHOGENESIS
1.
2.
3.
4.
Replicates initially in muscle and then enters peripheral nervous system
Spreads to CNS gray matter
Negri bodies found in neurons
Incubation period can be prolonged for months
III. RABIES: CLINICAL ASPECTS
A. MANIFESTATIONS
1. Average incubation period of 20 to 90 days
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2. Begins as a nonspecific illness marked by fever, headache, malaise, nausea, and
vomiting
3. Abnormal sensations at or around the site of viral inoculation occur frequently
and probably reflect local nerve involvement
4. Onset of encephalitis is marked by periods of excess motor activity and agitation
5. Hallucinations, combativeness, muscle spasms, signs of meningeal irritation,
seizures, and focal paralysis occur
6. Combination of excess salivation and difficulty in swallowing produces the
fearful picture of "foaming at the mouth."
7. Hydrophobia, the painful, violent involuntary contractions of the diaphragm and
accessory respiratory, pharyngeal, and laryngeal muscles initiated by swallowing
liquids
8. Once symptoms have developed, no drug or vaccine administration will improve
survival
9. Recovery is exceedingly rare.
B. DIAGNOSIS
1. Virus or antigen detected in brain tissue
2. Test of choice is detection of rabies antigen by immunofluorescent stain of a nape
of the neck biopsy
C. TREATMENT
1. Intensive supportive care has resulted in two or three long-term survivals
2. No specific treatment is available
D. PREVENTION
1. Pasteur, noting the long incubation period of rabies, suggested that a vaccine to
induce an immune response before the development of disease might be useful in
prevention
2. Now believed that vaccination induces antibody that is either neutralizing or
inhibits cell-to-cell spread of virus
3. Vaccine used in the United States for preexposure prophylaxis employs an
attenuated rabies virus grown in human diploid cell culture and inactivated
4. Preexposure prophylaxis is recommended for individuals at high risk of contact
with rabies virus, such as veterinarians, spelunkers, laboratory workers, and
animal handlers
5. Postexposure prophylaxis consideration of: (1) whether the individual came into
physical contact substance likely to contain rabies virus; (2) whether there was
significant wound or abrasion; (3) whether rabies is known or suspected in the
animal species (4) whether the bite was provoked or unprovoked; and (5) whether
the animal is available for laboratory examination
6. Rabies immune globulin plus vaccine necessary in postexposure management
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