Cache Valley virus is spread to people by the bite of an infected mosquito.
Mosquitoes become infected when they feed on mammals that have the virus in their blood. Infected mosquitoes can then spread the virus to people and other animals by biting them.
Cache Valley virus has been found in many types of mosquitoes, but it is not known which species are the main ones that spread the virus to humans. The mammals most likely involved in the transmission cycle are deer, cattle, horses, and sheep.
Cache Valley virus is not spread by coughing, sneezing, touching, or other contact with someone who is infected.