Rift valley fever

Background

• Viral illness caused by RVF virus, a bunyaviridae
• Primarily infects domesticated animals; cattle, sheep, buffalo, etc.
• Outbreaks related to unusually heavy rainfall and flooding
• Found mostly in eastern and southern Africa where domesticated animals are raised
  • Can be found in most of Africa
  • Recent outbreaks in Saudi Arabia and Yemen (first outside African continent)
• Outbreaks cause major economic impact with livestock death

Transmission

• Mosquitos, most commonly Aedes, are a reservoir and vector for RVF virus
  • Able to live with the virus and pass on to offspring, virus remains viable in eggs
  • Bite livestock and humans to cause infection
  • Increased rainfall increases mosquito numbers and is associated with outbreaks
• Humans are most commonly infected through direct contact of blood or other bodily fluids of infected livestock
  • Slaughter, veterinary procedures, obstetrical procedures
• No documented human to human transmission
• Aerosolized transfer has occurred in laboratory settings

Clinical Features

• Incubation period of 2-6 days
• Several different disease syndromes
  • Mild RVF
    • No symptoms or flu-like illness (fever, myalgias, joint pain, headache)
    • Early disease can be mistaken for meningitis with occasional neck stiffness and sensitivity to light
    • Resolves within 1 week
  • Severe RVF
    • Occular form- 0.5-2% of patients
      • Mild disease form + retinal lesions, blurred and decreased vision
      • Retinal lesions occur 1-3 weeks after disease onset and last 10-12 weeks
      • 50% of patients with macular lesions will develop permanent vision loss
    • Meningoencephalitis form- <1% of patients
      • Severe headache, memory loss, hallucinations, confusion, vertigo, seizures, coma, and late neurological complications
      • Onset is 1-4 weeks after mild symptoms
      • Residual severe neurological deficits are common
    • Hemorrhagic fever form- <1% of patients
      • Jaundice is first sign due to liver dysfunction
      • Hemorrhage (vomit, stool, gums, menorrhagia), purpuric rash, echymosis
      • Onset is 2-4 days after illness, death in 3-6 days
      • Most fatalities from RVF, 50% fatality rate

Differential Diagnosis

Fever in Traveler

• Normal causes of acute fever!
• Malaria
• Dengue
• Leptospirosis
• Typhoid Fever
• Typhus
• Viral Hemorrhagic Fevers
  • Ebola
  • Lassa fever
• Chikungunya
• Yellow fever
• Rift Valley Fever
• Q fever
• Meningitis- Early RVF can be hard to distinguish

Workup

• Pursue other possible causes of fever
• IgM ELISA, viral detection, and RT-PCR can be used to diagnose acute infection. IgG ELISA for previous infection.

Management

• Mild disease syndromes require no intervention and are self limited
• No specific treatment exists for severe disease forms
  • Supportive Care
    • Pain control
      • DO NOT use ASA in hemorrhagic form
  • IVFs
  • Blood Component Transfusion - consider in hemorrhagic shock
• Inactivated vaccine has been developed for humans
  • Not licensed and not commercially available
  • Experimental use on veterinary and lab workers
• Approved vaccines for livestock

Disposition

• Isolation precautions: standard, contact, and consider droplet
• Admit if severe form suspected, likely ICU
  • Consult ID
  • Consult ophthalmology for ocular form

See Also

• Fever in Travelers
• Travel Medicine

Sources

• http://www.who.int/mediacentre/factsheets/fs207/en/
• http://www.cdc.gov/vhf/rvf/index.html