What is Rift Valley fever?

Rift Valley fever is a zoonotic viral haemorrhagic fever caused by Rift Valley fever virus (RVFV) — transmitted primarily through mosquito bites and direct contact with infected animals or their tissues. It is primarily a disease of domestic livestock (cattle, sheep, goats, camels) causing devastating epizootics — but spills over to humans through contact with infected animals, their blood, tissue or milk, or through infected mosquito bites. Human disease ranges from mild febrile illness (majority) to severe complications including haemorrhagic fever, encephalitis and blinding retinitis.

How is RVF transmitted to humans?

Primary routes: direct contact with infected animal blood, tissues or fluids (particularly during slaughter, birthing, veterinary work — accounting for most human cases); consumption of raw unpasteurised milk from infected animals; and mosquito bites (multiple species can transmit RVFV). Highest-risk occupations: farmers, shepherds, abattoir workers, veterinarians. Person-to-person transmission: not documented through casual contact; potential risk from close blood exposure in healthcare settings (full PPE required for suspected cases).

What are the clinical forms?

Mild (most common — approximately 50-75% asymptomatic, most symptomatic cases): sudden fever (38-40°C), headache, myalgia, backache, anorexia — self-limiting over 4-7 days; low fatality. Ocular disease (1-10%): retinitis, chorioretinitis causing macular lesions → permanent central vision loss or blindness in approximately 50% of those affected; onset 1-4 weeks after fever. Meningoencephalitis (<1%): severe neurological disease — headache, hallucinations, seizures, coma; high morbidity. Haemorrhagic fever (<1%): jaundice, bleeding from multiple sites, liver failure — approximately 10-12% fatality in this subgroup.

What outbreaks of RVF have occurred?

Egypt 1977-78: the first large RVF outbreak outside sub-Saharan Africa — approximately 200,000 human infections, approximately 600 deaths, associated with Aswan Dam creating mosquito breeding habitats. Kenya/Tanzania/Somalia 1997-98: 89,000 estimated human cases, 478 deaths, triggered by El Niño rainfall. East Africa 2006-07: approximately 200,000 human infections, approximately 700 deaths — Kenya, Somalia, Tanzania. Saudi Arabia and Yemen 2000: first confirmed outbreak outside Africa — introduced through infected livestock imports. Outbreaks in Mauritania, South Sudan and Madagascar have occurred in subsequent years.

Can RVF be prevented?

Animal vaccination before anticipated outbreaks (based on rainfall prediction models) is the most impactful control measure — reducing the amplifying reservoir. Human prevention: avoidance of slaughtering or handling sick/dead animals during outbreaks (or use of protective clothing/gloves); pasteurisation of milk; insect repellents and protective clothing in endemic areas; mosquito control (larviciding during flooding). Healthcare precautions: standard and blood/body fluid precautions when caring for RVF patients. A human vaccine would transform prevention but none is currently approved.

Is RVF expanding its range?

RVF has demonstrated capacity to spread beyond its historical African range: Egypt (1977), Saudi Arabia and Yemen (2000) confirmed this. Climate change projections (warmer temperatures, altered rainfall patterns) and global livestock trade create conditions for further spread. Mathematical models predict RVF could become established in parts of Europe (Iberian Peninsula, Mediterranean) under certain climate scenarios. The WHO R&D Blueprint designation reflects recognition of RVF's epidemic potential beyond its current range.

How does GMJ News cover RVF?

GMJ News covers WHO RVF situation reports, East Africa outbreak data, climate-rainfall-outbreak connections, livestock vaccination strategies, retinitis outcomes, and vaccine development. RVF illustrates the One Health paradigm perfectly — livestock disease prevention is human disease prevention — directly relevant to PHIG's zoonotic disease mandate.

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Rift Valley Fever

Q: What outbreaks of RVF have occurred?

Egypt 1977-78: the first large RVF outbreak outside sub-Saharan Africa — approximately 200,000 human infections, approximately 600 deaths, associated with Aswan Dam creating mosquito breeding habitats. Kenya/Tanzania/Somalia 1997-98: 89,000 estimated human cases, 478 deaths, triggered by El Niño rainfall. East Africa 2006-07: approximately 200,000 human infections, approximately 700 deaths — Kenya, Somalia, Tanzania. Saudi Arabia and Yemen 2000: first confirmed outbreak outside Africa — introduced through infected livestock imports. Outbreaks in Mauritania, South Sudan and Madagascar have occurred in subsequent years.

Q: Can RVF be prevented?

Animal vaccination before anticipated outbreaks (based on rainfall prediction models) is the most impactful control measure — reducing the amplifying reservoir. Human prevention: avoidance of slaughtering or handling sick/dead animals during outbreaks (or use of protective clothing/gloves); pasteurisation of milk; insect repellents and protective clothing in endemic areas; mosquito control (larviciding during flooding). Healthcare precautions: standard and blood/body fluid precautions when caring for RVF patients. A human vaccine would transform prevention but none is currently approved.

Q: Is RVF expanding its range?

RVF has demonstrated capacity to spread beyond its historical African range: Egypt (1977), Saudi Arabia and Yemen (2000) confirmed this. Climate change projections (warmer temperatures, altered rainfall patterns) and global livestock trade create conditions for further spread. Mathematical models predict RVF could become established in parts of Europe (Iberian Peninsula, Mediterranean) under certain climate scenarios. The WHO R&D Blueprint designation reflects recognition of RVF's epidemic potential beyond its current range.

Q: How does GMJ News cover RVF?

GMJ News covers WHO RVF situation reports, East Africa outbreak data, climate-rainfall-outbreak connections, livestock vaccination strategies, retinitis outcomes, and vaccine development. RVF illustrates the One Health paradigm perfectly — livestock disease prevention is human disease prevention — directly relevant to PHIG's zoonotic disease mandate.

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

Summary Statistics Glossary GMJ news FAQ Documents Organizations Research

Rift Valley fever (RVF) — caused by Rift Valley fever virus (RVFV, a Phlebovirus) transmitted by mosquitoes and through direct contact with infected animals and their products — is a WHO R&D Blueprint priority pathogen causing major animal (livestock) epidemics and human disease across Africa and the Arabian Peninsula: most human infections cause mild febrile illness, but approximately 2% develop life-threatening complications including haemorrhagic fever, encephalitis and retinitis causing permanent blindness (WHO). RVF outbreaks cause devastating economic impact through livestock mortality and trade restrictions — with the 2006-2007 East Africa outbreak causing approximately 200,000 human infections and massive livestock losses.

Key messages

WHO R&D Blueprint priority pathogen

Rift Valley fever is on the WHO R&D Blueprint priority pathogen list — with potential for epidemic spread, severe animal and human disease, and no approved human vaccine or specific antiviral.

Primarily a livestock disease with major zoonotic spillover

RVF is primarily a disease of cattle, sheep, goats and camels — causing devastating livestock epidemics (mass abortion, neonatal death, up to 90-100% abortion in infected herds). Human cases occur through direct contact with infected animals and their products, or through mosquito bites.

Most infections mild — 2% life-threatening

Approximately 50-75% of human RVF infections are asymptomatic; most symptomatic cases cause mild self-limiting febrile illness. However, approximately 2% develop severe life-threatening complications: haemorrhagic fever; encephalitis; or retinitis (eye inflammation) causing permanent blindness in approximately 1-10% of cases.

Climate variability drives outbreaks

RVF outbreaks follow heavy rainfall and flooding — which trigger massive mosquito population explosions and amplify virus transmission. The 2006-2007 East Africa outbreak coincided with record rainfall; approximately 200,000 human infections occurred.

Expanding geographic range

RVF was historically confined to Sub-Saharan Africa; it spread to Egypt (1977 outbreak — approximately 600 deaths), Saudi Arabia and Yemen (2000 — first outbreak outside Africa), and continues to expand. Climate change and trade in infected animals threaten further spread.

No approved human vaccine

Multiple RVF vaccine candidates are in development — live attenuated (MP-12 — used in veterinary practice), inactivated, virus-like particle, mRNA vaccines. Veterinary vaccination of livestock is the primary outbreak control strategy (vaccinating animals reduces the reservoir before human cases).

Key statistics

~200K

human infections estimated in 2006-2007 East Africa outbreak

WHO

~2%

of infections develop severe disease (VHF, encephalitis, retinitis)

WHO

1-10%

develop permanent retinitis/blindness

WHO

10-12%

case fatality in severe haemorrhagic form

WHO

approved human RVF vaccines

WHO 2024

2000

year RVF first confirmed outside Africa (Saudi Arabia, Yemen)

WHO

Major Rift Valley fever outbreaks — approximate human cases by year and location

Source: WHO RVF situation reports. Outbreaks cluster with heavy rainfall events.

Glossary of key terms

Rift Valley fever virus (RVFV)
WHOA Phlebovirus (Bunyavirales) — named after the Rift Valley in Kenya where it was first identified in 1930. Infects livestock (cattle, sheep, goats, camels), humans and other animals. Multiple mosquito species transmit RVFV (primarily Aedes, Culex genera); vertical transmission in mosquito eggs allows virus survival between outbreaks.

Retinitis in RVF
WHO/OphthalmologyA distinctive severe complication of RVF — occurring 1-4 weeks after febrile illness in approximately 1-10% of symptomatic cases. RVFV causes chorioretinitis, vasculitis and macular scarring — leading to permanent visual loss or blindness (approximately 50% of those with retinitis have permanent vision impairment). No proven treatment.

Epizootic (animal epidemic)
WHO/WOAHAn epidemic of infectious disease in an animal population. RVF causes devastating epizootics in livestock: abortion rates approaching 100% in pregnant cattle, sheep and goats; neonatal death (up to 90% mortality in newborn lambs); adult mortality approximately 10-30% in sheep. The livestock mortality and abortion wave typically precedes the human outbreak.

Transovarial transmission
WHOVertical transmission of RVFV from infected female Aedes mosquitoes to offspring through eggs — allowing virus to survive dry periods in desiccation-resistant eggs. When flooding occurs and eggs hatch, infected mosquitoes emerge, initiating the next epizootic cycle. This explains the close correlation between RVFV outbreaks and heavy rainfall/flooding.

RVF livestock vaccination
WOAH/WHOVaccination of cattle, sheep and goats before predicted RVF outbreaks (triggered by rainfall forecasting) is the primary control measure — reducing the amplifying animal reservoir and subsequent human spillover. Live attenuated Smithburn vaccine (rapid protection, single dose — but risk of abortion in pregnant animals); inactivated vaccines (safer in pregnancy, require 2 doses).

MP-12 vaccine
WHO/USAMRIIDA live attenuated RVF vaccine — developed from a virulent RVFV strain attenuated by 12 serial passages in medium containing 5-fluorouracil. Used experimentally in humans (IND status only) and for US military personnel. Effective in animal models; safety in pregnant humans uncertain.