Rift Valley Fever
Rift Valley Fever (RVF) is a viral zoonosis that causes fever. It is spread through infected mosquitoes. It was first reported in 1915 in Kenya were it infected livestock. Outbreaks occur across sub-Saharan Africa, and in the “˜77-“˜78 outbreak several million people were infected and thousands died during a violent epidemic. In 1998 the virus killed 400 Kenyans and in 2000 an outbreak occurred in Saudi Arabia and Yemen.
The virus causes mild illness with fever, headache, myalgia and liver abnormalities. In a few patients illness can progress to hemorrhagic fever syndrome or meningoencephalitis. Patients usually recover 2-7 days after onset. Only about 1% of human sufferers die of the disease.
Livestock fatality rates are much higher. Pregnant livestock that get infected with RVF have a 100% abortion rate thus a wave of unexplained abortions is a pre-cursor to an RVF infection. There are several animal vaccines to protect against RVF infection. The first vaccine provide immunity for 3 years however it led to abortion of pregnant ewes in many cases and was thus dumped for attenuated vaccines. These vaccines only work after multiple inoculations.