From the World Health Organzation

Key Points

  • 4 January 2019
  • The National IHR Focal Point for France informed WHO of five human cases of Rift Valley Fever (RVF) diagnosed on Mayotte Island through the Early Warning and Response System of the European Union
  • The dates of symptom onset ranged from 22 November to 31 December 2018 (WHO)


During the reporting period November 2018 to 03 May 2019

  • 129 confirmed human Rift Valley Fever (RVF) cases
  • 109 animal foci (23 small ruminants and 86 bovine) have been reported in Mayotte
  • After a steady decline in cases during the last three weeks of March 2019
  • A slight increase has been observed in April 2019 (WHO)


WHO Risk Assessment

  • RVF virus has been circulating actively on the island of Mayotte
  • The virus is a regular import from nearby countries through illegal animal movements
  • The presence of susceptible animals and a favorable environment for mosquito vectors to maintain virus transmission locally
  • RVF virus is primarily transmitted by mosquitoes
  • Mayotte, has a notable species richness of mosquitoes with 45 documented specie
  • While the main route of infection of humans is through direct or indirect contact with the blood, body fluids, tissues and organs of infected animals and aborted animal fetuses
  • It is highly contagious for humans when handling infected livestock
  • The high-risk groups including veterinarians, livestock farmers and butchers should conduct safe animal husbandry and slaughtering practices to prevent infections
  • To date, no human-to-human transmission of RVF virus has been reported


About Rift Valley Fever

No vaccines are currently available for human vaccination

  • Rift Valley fever (RVF) is an acute, fever-causing viral disease most commonly observed in domesticated animals (such as cattle, buffalo, sheep, goats, and camels), with the ability to infect and cause illness in humans (CDC)
  • The disease is caused by RVF virus, a member of the genus Phlebovirus in the family Bunyaviridae



  • Humans can be infected with RVF from bites of infected mosquitoes and, rarely, from other biting insects that have virus-contaminated mouthparts
  • More commonly, humans are infected after exposure to blood, body fluids, or tissues of RVF-infected animals. This direct exposure to infected animals can occur during slaughter or through veterinary and obstetric procedures
  • Infection through aerosol transmission of RVF virus has occurred in the laboratory environment (CDC)


Signs & Symptoms

  • RVF virus has an incubation period of 2-6 days following infection
  • Most commonly, people with RVF have either no symptoms or a mild illness associated with fever and liver abnormalities
  • Patients who become ill usually experience fever, generalized weakness, back pain, and dizziness at the onset of the illness
  • Typically, patients recover within two days to one week after onset of illness (CDC)


A Small percentage (less than 8%) of people infected with RVF develop

  • Ocular disease (diseases affecting the eye), Lesions on the eyes may occur 50% of patients will have permanent vision loss
  • Encephalitis, or inflammation of the brain, which can lead to headaches, coma, or seizures
  • Though death from this is rare, neurological deficits, sometimes severe, may persist
  • Hemorrhagic fever, which occurs in less than 1% of overall RVF patients
  • Fatality for those who do develop these symptoms, is around 50%
  • Symptoms of hemorrhaging may begin with jaundice and other signs of liver impairment, followed
    by vomiting blood, bloody stool, or bleeding from gums, skin, nose, and injection sites (CDC)



  • Because most human cases of RVF are mild and self-limiting, a specific treatment for RVF has not been established
  • The rare, but serious, cases are generally limited to supportive care
  • The most common complication associated with RVF is inflammation of the retina (a structure connecting the nerves of the eye to the brain)
  • As a result, approximately 1% – 10% of affected patients may have permanent vision loss (CDC)



  • A person’s chances of becoming infected can be reduced by taking measures to decrease contact with blood, body fluids, or tissues of infected animals
  • Protecting themselves against mosquitoes and other bloodsucking insects
  • Use of mosquito repellents and bednets are two effective methods
  • For persons working with animals in RVF-endemic areas, wearing protective equipment to avoid
    any exposure to blood or tissues of animals that may potentially be infected is an important protective measure (CDC)




WHO  https://www.who.int/csr/don/13-may-2019-rift-valley-fever-mayotte-france/en/

CDC  https://www.cdc.gov/vhf/rvf/RVF-FactSheet.pdf