Phylogenetic relationships were examined for 198 Rift
Valley fever virus isolates and 5 derived strains obtained
from various sources in Saudi Arabia and 16 countries in
Africa during a 67-year period (1944–2010). A maximumlikelihood
tree prepared with sequence data for a 490-nt
section of the Gn glycoprotein gene showed that 95 unique
sequences sorted into 15 lineages. A 2010 isolate from a
patient in South Africa potentially exposed to co-infection
with live animal vaccine and wild virus was a reassortant.
The potential influence of large-scale use of live animal
vaccine on evolution of Rift Valley fever virus is discussed.