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Human rabies

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At a glance

  • Reporting timeframe: Immediately (by phone within 4 hours of suspected diagnosis)
  • Individual cases need follow-up? Yes
  • Timeline for patient interview: 24 hours
  • Responsibility for investigation: CDPHE
  • CDPHE Program: Zoonoses and One Health
  • Mode(s) of transmission: 
    • Bite resulting in infected saliva breaking through the skin
    • Infected saliva contact with mucous membranes or open wounds


 

 

  • Incubation period: Typically 3-12 weeks but ranges from days to years
  • Infectious period: Human-to-human transmission has not been reported in the United States, although it is theoretically possible.
  • Treatment: none
  • Prophylaxis: rabies post-exposure prophylaxis series 
  • Exclusion criteria: none

Contents

Reporting criteria

What and how to report to the Colorado Department of Public Health and Environment (CDPHE) or local public health agency

Any physician who suspects they have a human patient with symptomatic rabies should report to CDPHE by phone immediately. 

Purpose of surveillance and reporting

To prevent exposures to rabies and make recommendations for rabies post-exposure prophylaxis to those who have been exposed.

The disease and its epidemiology

Etiologic agent

Rabies virus

Clinical description

The first symptoms of rabies may be like the flu, including weakness or discomfort, fever, or headache. There also may be discomfort, prickling, or an itching sensation at the site of the bite. These symptoms may last for several days. Usually, severe disease appears within two weeks of the first symptoms, when the rabies virus causes brain dysfunction. Common signs include anxiety, confusion, agitation, and hallucinations. Once clinical signs of rabies appear, the disease is nearly always fatal, and treatment is typically supportive.

Reservoirs

  • Bats (throughout Colorado)
  • Skunks (from the eastern plains to the foothills)
  • In other parts of the country: foxes and raccoons
  • Internationally: dogs

Modes of transmission

Rabies is transmitted when saliva from an infected animal enters the body via a bite or contact with mucous membranes. Rabies is not transmitted by salivary contact with intact skin or by contaminated objects or materials like clothing. 

Incubation period

Usually 3-12 weeks, but the incubation period has ranged from days to years.

Infectious period

Contacts from the 14 days preceding symptom onset should be evaluated for exposure.

Epidemiology

The last case of human rabies in Colorado was in 1931. There are between one and three cases in residents of the United States per year resulting from exposure to bats or international dog bites.

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Case definition

Clinical description

Rabies is an acute encephalomyelitis that almost always progresses to coma or death within 10 days after the first symptom.

Laboratory criteria for diagnosis

  • Detection by direct fluorescent antibody of viral antigens in a clinical specimen (preferably the brain or the nerves surrounding hair follicles in the nape of the neck), or
  • Isolation (in cell culture or in a laboratory animal) of rabies virus from saliva, cerebrospinal fluid (CSF), or central nervous system tissue, or
  • Identification of a rabies-neutralizing antibody titer greater than or equal to 5 (complete neutralization) in CSF, or
  • Identification of a rabies-neutralizing antibody titer greater than or equal to 5 (complete neutralization) in the serum of an unvaccinated person.

Case classification

Confirmed

  • A clinically compatible case that is laboratory confirmed.

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Laboratory testing

Human rabies testing can only be done at CDC. Physicians must first consult with a member of the Zoonoses and One Health Program team at CDPHE. CDPHE will determine if the case should be presented to CDC for testing. Postmortem testing can be done at CDC with approval through the Zoonoses and One Health Program.

Antemortem testing requires four clinical specimens:

  1. Cerebrospinal fluid
  2. Serum
  3. Saliva
  4. Skin biopsy of the hairline at the nape of the neck 

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Case investigation

Cases are unlikely to be well enough for an interview. Instead, family or other members of the case’s household should be interviewed to determine: 

  • Exposure to animals going back at least 12 weeks
  • Occupational history with attention to potential wildlife exposures 
  • Rabies post-exposure prophylaxis history 
  • Symptom description, onset, progression

Forms 

CDC Possible Human Rabies Patient Information Form

Identify and evaluate contacts (if applicable, as not all pathogens are communicable)

Contacts with potential salivary exposure in the two weeks prior to symptom onset should be evaluated for rabies post-exposure prophylaxis.

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Disease control measures

Treatment

None available 

Prophylaxis

Rabies vaccine and immunoglobulin, when administered appropriately, will prevent rabies symptoms and death.

Environmental measures

None

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References

Centers for Disease Control and Prevention rabies webpage

Important telephone and fax numbers

CDPHE Communicable Disease Branch

  • Phone: 303-692-2700 or 800-866-2759
  • Fax: 303-782-0338
  • After hours: 303-370-9395

CDPHE Microbiology Laboratory: 303-692-3480

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