Distribution of<unk>  in Africa: Blue, countries with endemic disease and substantial outbreaks of<unk> ; green, countries known to have some cases, periodic isolation of virus, or serologic evidence of<unk> <unk>  outbreaks occur across sub-Saharan Africa, with outbreaks occurring elsewhere infrequently. Outbreaks of this disease usually correspond with the warm phases of the EI Niño/Southern Oscillation. During this time there is an increase in rainfall, flooding and greenness of vegetation index, which leads to an increase in mosquito vectors.<unk> V can be transmitted vertically in mosquitos, meaning that the virus can be passed from the mother to her offspring. During dry conditions, the virus can remain viable for a number of years in the egg. Mosquitos lay their eggs in water, where they eventually hatch. As water is essential for mosquito eggs to hatch, rainfall and flooding cause an increase in the mosquito population and an increased potential for the virus. The first documented outbreak was identified in Kenya in 1931, in sheep, cattle and humans; another severe outbreak in the country in 1950–1951 involved 100,000 deaths in livestock and an unrecorded number of humans with fever. An outbreak occurred in South Africa in 1974–1976, with more than 500,000 infected animals and the first deaths in humans. In Egypt in 1977–78, an estimated 200,000 people were infected and there were at least 594 deaths. In Kenya in 1998, the virus killed more than 400 people. Since then, there have been outbreaks in Saudi Arabia and Yemen (2000), East Africa (2006–2007), Sudan (2007), South Africa (2010), Uganda (2016), Kenya (2018), and Mayotte (2018–2019). In 2020–2021, an outbreak is ongoing in Kenya.
Rift Valley fever
Chikungunya
Zika fever
Ross River fever
Malaria
Yellow fever
Trench fever
Blackwater fever