RVF-like disease early in 1912-1913 near Lake Naivasha (Great Rift Valley) in Kenya was described by Montgomery and Stordy. But it was later in 1931 that the RVF virus was first isolated during a <a href="http://www.websters-online-dictionary.org/definition/english/Ep/Epizootic.html" target="_blank">epizooty in the same area.

In East Africa, RVF outbreaks were known to follow periods of abnormally high rainfall (<a href="http://www.ncbi.nlm.nih.gov/pubmed/11426274" target="_blank"> Linthicum and al., 1999). Outbreaks has since occurred in many other African countries, pretty much associated with climate disorder or environment change.

Evidence of RVF virus activity in West Africa (Southeastern Mauritania) has been denoted early in 1933 (Stefanoppoulo, 1933; Curasson, 1934; Findlay and al., 1936). After the epidemic event in 1987, a monitoring network involving many partners (S2E in EMERCASE project, DIREL, …) was created in Senegal (i.e; RVF events at the end of this page).

Some countries surrounded by other ones where RVF is an endemic disease seem to be safe. We guess this relative safety is due to a lack of monitoring rather than a lack of RVF virus activity.

An epizootic of RVF is generally observed during years in which unusually heavy rainfall and localized flooding occur. The excessive rainfall allows mosquito eggs, usually of the genus Aedes, to hatch. The mosquito eggs are naturally infected with the RVF virus, and the resulting mosquitoes transfer the virus to the livestock on which they feed. Once the livestock is infected, other species of mosquitoes can become infected from the animals and can spread the disease. In addition, it is possible that the virus can be transmitted by other biting insects.

Hereafter cases and years of RVF events

• Kenya, 1930-1931, 1951, 1998.
• South Africa, 1950-1951, 1958, 1974-1976, 1981, 1991, 1999
• Zimbabwe, 1958, 1999, 2001. ( information in OIE archives )

• Nigeria, 1967.
• Chad, 1967, rainy seasons 2001 and 2002. Article on CDC website
• Sudan, 1973-1976.
• Zambia, 1975, 1997.
• Egypt, 1977-1978, 1993 (after opening the Aswan Dam), 1997, 2003
• Tanzania, 1978, 1998.
• Madagascar, 1979, 1991, 1999.
• Mauritania, 1987, 1993, 1998, 2002, 2003.
• Senegal, 1987, 1993, 1994, 1998, 2002, 2003, 2004.
• Somalia , 1997.
• Yemen-> , 2000.
• Saudi Arab->ia, 2000, 2004.
• Gambia, 2003.

More information about :

• <a href="http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/rvf.htm" target="_blank">CDC website
• <a href="http://www.who.int/csr/don/archive/disease/rift_valley_fever/en/" target="_blank">OMS / WHO website
• <a href="http://www.oie.int/eng/maladies/fiches/a_A080.htm" target="_blank">OIE website