Rift Valley fever virus particles, computer illustration. This virus particle consists of an RNA (ribonucleic acid) genome enclosed in a protein capsid, which is itself surrounded by a glycoprotein envelope. Rift Valley fever occurs in Africa, infecting humans, cattle, sheep, rodents and other species. It is transmitted by insects, mainly mosquitoes, and causes chills, fever, a headache and joint and muscle pain. It is rarely fatal, but can cause retinal haemorrhages that may lead to visual impairment.