Rabies

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 86.6% of rabid animals in 2018

  • 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 ...