Rift Valley Fever
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U.S. Threat Level
Low. Rift Valley fever was initially found in Kenya, but by 2010 it had spread to almost the entire African continent. Authorities expect Europe and the U.S. to be next.

How It Spreads
Mosquitoes, as well as exposure to the blood or bodily fluids of infected animals, such as during slaughter or veterinary work.

What It Does 
Fever, headache, muscle pain, dizziness, vision loss, and encephalitis (inflammation of the brain, which can lead to coma and seizures).