Figure 1.

The transmission cycle of encephalitic alphaviruses. A) Alphaviruses are maintained in nature by cycling between a host species, typically a bird or small mammal, and a mosquito vector species. B) Spillover events often occur into livestock, which reach high viral titers and readily transmit the virus to additional vectors. In the case of the New-World viruses this infection almost always leads to death²⁷. C) Typically, after infection of livestock, humans that work in close association with these animals can also be infected by vector species. Humans are regarded as dead-end hosts for most alphaviruses. In humans these infections may lead to disease, and, in severe cases, death.