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For further information, see CMDT Part 32-03: Other Neurotropic Viruses

Key Features

Essentials of Diagnosis

  • History of animal bite

  • Paresthesias, hydrophobia, rage alternating with calm

  • Convulsions, paralysis, thick tenacious saliva

General Considerations

  • Rabies is a viral (rhabdovirus) encephalitis transmitted by infected saliva that enters the body by an animal bite or an open wound

  • The virus enters the salivary glands of dogs 5–7 days before their death from rabies, thus limiting their period of infectivity

  • Less common routes of transmission include

    • Contamination of mucous membranes with saliva or brain tissue

    • Aerosol transmission

    • Corneal transplantation

  • Incubation period

    • May range from 10 days to many years

    • However, it is usually 3–7 weeks depending in part on the distance of the wound from the CNS

  • The virus travels via the nerves to the brain, multiplies there, and then migrates along the efferent nerves to the salivary glands

  • Rabies virus infection forms cytoplasmic inclusion bodies similar to Negri bodies

  • These Negri bodies are thought to be the sites of viral transcription and replication

Demographics

  • Worldwide, over 17 million cases of animal bites are reported every year, and it is estimated that about 59,000 deaths annually are attributable to rabies

  • Rabies is endemic in over 150 countries; it is estimated that over 40% of the world's population lives in areas without rabies surveillance

  • Most cases of rabies occur in rural areas of Africa and Asia

  • India has the highest incidence, accounting for 36% of global deaths

  • In the United States,

    • Raccoons, bats, and skunks accounted for 82% of the rabid animals

    • Other rabid animals include foxes, cats, cattle, and dogs

Clinical Findings

  • The prodromal syndrome

    • Consists of pain at the site of the bite in association with fever, malaise, headache, nausea, and vomiting

    • Skin is sensitive to changes of temperature, especially air currents (aerophobia)

    • Percussion myoedema (a mounding of muscles after a light pressure stimulus) can be present and persist throughout the disease

    • Abnormal sexual behavior is a recognized presenting symptom of rabies and such behavior includes priapism and frequent ejaculation in males and hypersexuality in females

  • The CNS stage begins about 10 days after the prodrome and may be either encephalitic or paralytic

  • The encephalitic form (about 80% of the cases) produces the classic rabies manifestations of delirium alternating with periods of

    • Calm

    • Extremely painful laryngeal spasms on attempting drinking (hydrophobia)

    • Autonomic stimulation (hypersalivation)

    • Seizures

  • In the less common paralytic form, an acute ascending paralysis resembling Guillain-Barré syndrome predominates with relative sparing of higher cortical functions initially

  • Both forms progress to coma, autonomic nervous system dysfunction, and death

Diagnosis

  • Biting animals that appear well should be quarantined and observed for 10 days

  • Sick or dead animals should be tested for rabies

  • When the animal cannot be ...

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