Breaking the chain: Rift Valley fever virus control via livestock vaccination

Rift Valley fever virus is a mosquito-borne pathogen of livestock and humans that causes widespread and devastating outbreaks of severe and often fatal disease throughout Africa and portions of the Arabian Peninsula. Outbreaks can involve tens to hundreds of thousands of human cases, and millions of livestock. The severity of the disease varies by species, but in sheep and cattle 'abortion storms', high neonatal (∼70%), and adult mortality (20-30%) are features. Human cases are generally self-limiting, but severe complications such as hepatitis, retinitis, delayed-onset encephalitis, or a hemorrhagic syndrome with a case fatality of 10-20% can occur. There are no commercially available human vaccines. Livestock provide key ecological links between the Aedes sp. mosquito vector and humans. High viremias in livestock lead to spillover of RVFV into other anthrophillic vectors (Culex and Anopheles sp. mosquitoes), and, importantly, close contact with infected animal tissues and fluids or aborted fetal materials from these animals is a major risk factor for severe and lethal human infections. Vaccination programs targeting livestock during non-epidemic periods or as an early countermeasure against nascent outbreaks could therefore eliminate one of the main sources of human infection and limit the overall scope of epidemics. To this end, research groups have recently reported novel next generation RVFV vaccines that are safe for use in pregnant and young animals. Preventing RVFV infection of livestock by vaccination is a key element in breaking the chain of human epidemics, and could lead to control of this significant public health threat.