Rift Valley Fever
The Rift Valley Fever (RVF) is a viral zoonosis (disease transmitted from animals to humans) that primarily affects animals, but also has the capacity to infect humans. Infection can cause severe disease and death in both animals and humans. The disease also results in significant economic losses due to death and abortion among RVF-infected livestock. Rift Valley Fever virus (RVFV) virus is a member of the Phlebovirus genus, one of the five genera in the family Bunyaviridae.
The virus was first identified in 1931 during an investigation into an epidemic among sheep on a farm in the Rift Valley of Kenya. Since then, outbreaks have been reported in sub-Saharan and North Africa. In 1997-98, a major outbreak occurred in Kenya, Somalia and Tanzania and in September 2000, RVF cases were confirmed in Saudi Arabia and Yemen, marking the first reported occurrence of the disease outside the African continent and raising concerns that it could extend to other parts of Asia and Europe. Most human infections result from direct or indirect contact with the blood or organs of infected animals, including aerosolized materials, and certain occupational groups such as herders, farmers, slaughterhouse workers and veterinarians are at higher risk of infection. There is some evidence that humans may also become infected with RVFV by ingesting the unpasteurized or uncooked milk of infected animals, or through the bites of infected mosquitoes, most commonly the Aedes mosquito. To date, no human-to-human transmission of RVFV has been documented.
The incubation period (interval from infection to onset of symptoms) for RVF varies from two to six days. Those infected either experience no detectable symptoms or develop a mild form of the disease characterized by a feverish syndrome with sudden onset of flu-like fever, muscle pain, joint pain and headache. Some patients develop neck stiffness, sensitivity to light, loss of appetite and vomiting; in these patients the disease, in its early stages, may be mistaken for meningitis. While most human cases are relatively mild, a small percentage of patients develop a much more severe form of the disease. The total case fatality rate has varied widely between different epidemics but, overall, has been less than 1% in those documented. Most fatalities occur in patients who develop the haemorrhagic icterus form.
Rift Valley Fever Vaccines
The need for mass vaccination against RVF is limited due to the lack of human-to-human transmission of RVF. An inactivated vaccine has been developed for human use, but it is not licensed and or commercially available. It has been used experimentally to protect veterinary and laboratory personnel at high risk of exposure to RVF. Other candidate vaccines are under investigation.
Rift Valley fever vaccine standardization
WHO developed guidance on the regulatory control of RVF vaccines in 1981 following an outbreak of RFV in Egypt in 1977.
No WHO reference materials for rift valley fever vaccines are currently available.