Rift Valley fever (RVF) is a viral zoonosis that primarily affects animals but also has the capacity to infect humans. It is transmitted by mosquitoes and blood feeding flies. In humans, the disease ranges from a mild flu-like illness to severe haemorrhagic fever that can be lethal. When livestock are infected the disease can cause significant economic losses due to high mortality rates in young animals and waves of abortions in pregnant females. While some human infections have resulted from the bite of infected mosquitoes, most human infections result from contact with the blood or organs of infected animals. Occupational groups such as herders, farmers, slaughterhouse workers and veterinarians are at higher risk of infection. Humans may also become infected by ingesting the unpasteurized or uncooked milk of infected animals. No human-to-human transmission of RVF has been documented.