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Rift Valley Fever (RVF)

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Rift Valley Fever (RVF) is an acute, fever-causing disease caused by RVF virus, a bunyavirus that is transmitted via mosquitoes to domestic livestock. Human infections can result from mosquito bites as well as direct or indirect contact with the blood or organs of infected animals (care or slaughter of infected animals and possibly from ingestion of raw milk). It was first recognized in the 1900's in Kenya, Africa among domestic sheep. In 1931, the agent causing RVF was isolated from infected sheep. Those primarily affected are domestic livestock and humans in endemic areas of Africa.

  • Symptoms and Treatment in Humans
  • Symptoms in Domestic Animals
  • Transmission
  • RVF Occurrence in Florida
  • Resources and References

Symptoms

Once a human host is infected the incubation period to the onset of illness is about 2-6 days. Humans experience flu-like symptoms, which may include fever, weakness, weight loss, dizziness, headache, nausea, vomiting, and muscle and joint pain.

About 1% of those infected experience more severe symptoms. These symptoms include: retinal inflammation, brain inflammation, or hemorrhagic fever. Onset of hemorrhagic fever results in 50% mortality in about 3-6 days after infection of the host.

Treatment

Treatment typically includes supportive care and the use of experimental antiviral drugs. At this time the United States does not have a licensed human or animal vaccine.

The virus is typically recognized in domestic animal populations through symptoms consisting of elevated temperatures, increased rates of abortions, and high mortality rates among young animals.

Mosquitoes act as the vector for RVF and transmit the virus by feeding on the potential host. Once a host is infected they have the potential to infect other mosquito vectors via a blood meal. Aedes species mosquitoes are the primary vector. However, the Anopheles, Culex, and possibly other mosquito species can also become infected and act as vectors for the virus. To date, no human-to-human transmission of RVF has been documented.

Although RVF is currently not present in Florida, the state of Florida has optimal conditions to support such a virus. Florida has tropical and sub-tropical areas throughout the state, where increased amounts of rainfall can aid in increasing vector populations. Florida also has the same species of mosquito vectors that cause the endemic rates of RVF in parts of Africa. Methods of RVF introduction into Florida can be through trade routes and may include importation of infected animals or an infected mosquito vector. Due to the potential for RVF to become endemic if introduced into Florida, surveillance for this and other diseases is important to prevent the spread of disease.

RVF is endemic to parts of Africa with tropical and sub-tropical environments. Outbreaks typically occur or peak in late summer, especially after periods of heavy or unusual amounts of rainfall. In East Africa, outbreaks have been closely associated with the heavy rainfall that occurs during the warm phase of the El Niño/Southern Oscillation (ENSO) phenomenon. In 1997-1998, Kenya and Somalia experienced the largest outbreak reported and the first outbreak outside of Africa occurred in Saudi Arabia and Yemen in 2000-2001.

Resources

Florida Agricultural Response Team

Centers for Disease Control and Prevention Rift Valley Fever Fact Sheet

World Health Organization

References

Sissoko, Daouda. et. al. Rift Vally Fever, Mayotte, 2007-2008.

Emerging Infectious Disease. Vol.15, No.4; 568-570: 2009.

Hartley DM, Rinderknecht JL, Nipp TL, Clarke NP, Snowder GD; National Center for Foreign Animal and Zoonotic Disease Defense Advisory Group. Potential effects of Rift Valley fever in the United States. Emerg Infect Dis. 2011 Aug

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