title: Sequential Rift Valley fever outbreaks in eastern Africa caused by multiple lineages of the virus.
abstract: BACKGROUND
  During the Rift Valley fever (RVF) epidemic of 2006-2007 in eastern Africa, spatial mapping of the outbreaks across Kenya, Somalia, and Tanzania was performed and the RVF viruses were isolated and genetically characterized.
  
  
  METHODS
  Following confirmation of the RVF epidemic in Kenya on 19 December 2006 and in Tanzania on 2 February 2007, teams were sent to the field for case finding. Human, livestock, and mosquito specimens were collected and viruses isolated. The World Health Organization response team in Kenya worked with the WHO's polio surveillance team inside Somalia to collect information and specimens from Somalia.
  
  
  RESULTS
  Seven geographical foci that reported hundreds of livestock and >25 cases in humans between December 2006 and June 2007 were identified. The onset of RVF cases in each epidemic focus was preceded by heavy rainfall and flooding for at least 10 days. Full-length genome analysis of 16 RVF virus isolates recovered from humans, livestock, and mosquitoes in 5 of the 7 outbreak foci revealed 3 distinct lineages of the viruses within and across outbreak foci.
  
  
  CONCLUSIONS
  The findings indicate that the sequential RVF epidemics in the region were caused by multiple lineages of the RVF virus, sometimes independently activated or introduced in distinct outbreak foci.
authors.affiliation: Global Disease Detection Division, United States Centers for Disease Control and Prevention-Kenya, Nairobi, Kenya.
authors.forename: Leonard
authors.initials: L
authors.lastname: Nderitu
authors.forename: John S
authors.initials: JS
authors.lastname: Lee
authors.forename: Jared
authors.initials: J
authors.lastname: Omolo
authors.forename: Sylvia
authors.initials: S
authors.lastname: Omulo
authors.forename: Monica L
authors.initials: ML
authors.lastname: O'Guinn
authors.forename: Allen
authors.initials: A
authors.lastname: Hightower
authors.forename: Fausta
authors.initials: F
authors.lastname: Mosha
authors.forename: Mohamed
authors.initials: M
authors.lastname: Mohamed
authors.forename: Peninah
authors.initials: P
authors.lastname: Munyua
authors.forename: Zipporah
authors.initials: Z
authors.lastname: Nganga
authors.forename: Kelli
authors.initials: K
authors.lastname: Hiett
authors.forename: Bruce
authors.initials: B
authors.lastname: Seal
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Feikin
authors.forename: Robert F
authors.initials: RF
authors.lastname: Breiman
authors.forename: M Kariuki
authors.initials: MK
authors.lastname: Njenga
mesh_terms: D000351:Africa, Eastern / Q000453:epidemiology; D000818:Animals; D009033:Culicidae / Q000821:virology; D030561:Databases, Nucleic Acid; D004196:Disease Outbreaks; D005843:Geography; D006801:Humans; D011891:Rain; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012295:Rift Valley Fever / Q000453:epidemiology* / Q000635:transmission / Q000821:virology*; D012296:Rift Valley fever virus / Q000235:genetics* / Q000302:isolation & purification; D012307:Risk Factors; D017421:Sequence Analysis; D014944:World Health Organization