Rift valley fever historical perspective

Rift valley fever was predominantly seen in the African continent and Arabian peninsula since the 1950s. The RVF virus was discovered in 1930 when it was seen to cause liver infection in large numbers of sheep. Only after 1975, was Rift valley fever considered a disease of humans as before 1975 it was majorly considered a disease of African livestock. Various outbreaks of RVF have taken place in Africa since the 1950s, causing a deep socio-economic impact on the regions affected.

• In the year 1930, Rift Valley fever virus (RVFV) was discovered as the pathogen causing an increased incidence of hepatitis in animals belonging to the Rift Valley in Kenya.^[1]
• The primarily affected animals were sheep, with deaths and miscarriages in sheep along with mortality in lambs born recently.
• Blood from diseased sheep was injected in healthy sheep which then replicated to symptoms of the disease.
• It was also noted that many diseased sheep belonged to areas heavily infested with mosquitos. Therefore, to test this hypothesis, all the healthy sheep were moved to an area with low to no mosquitos, which when showed no symptoms of the disease, confirmed the hypothesis that the disease was transmitted from animal to animal (directly) or through mosquitos.^[2]
• Upon further investigation, many farmers and herders taking care of these diseased sheep reported symptoms of fever and body aches. This suggested the possibility of human susceptibility which was confirmed in a similar manner when healthy humans developed symptoms when blood from ill sheep was transfused to humans.
• The outbreaks of Rift valley fever were noted to be occurring in regions which received heavy rainfall. These environment and climate conditions enhance the breeding of mosquitos, which play an essential role in transmission of the virus to both humans and animals.

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