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

Mild

• 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

• 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 virus disease
  • Marburg virus disease
  • Lassa fever
  • Crimean-Congo hemorrhagic fever
• Chikungunya
• Yellow fever
• Rift Valley Fever
• Q fever
• Amebiasis
• Zika virus

Evaluation

• 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: requires no intervention (self limited_
• Severe
  • Supportive Care
    • Pain control
      • DO NOT use ASA in hemorrhagic form
  • IVFs
  • Blood Component Transfusion - consider in hemorrhagic shock

Vaccines

• 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

External Links

• WHO - Rift Valley Fever
• CDC - Rift Valley Fever

References

Authors

Colin Hoff, Ross Donaldson, Neil Young