During winter months in cold climates the vector numbers decrease or the vector disappears. Thus arbovirus infections tend to be epidemic and seasonal based on the presence of a large number of infected vectors during warmer months. Equines and humans are usually dead end hosts. Transmission from human to human does not occur and vector transmission among humans usually does not occur because levels of virus in the blood are very low or undetectable. Exceptions include Dengue and Yellow Fever where virus levels in the blood are sufficient for man to vector to man transmission.
Arboviral infections can manifest as three types of illnesses in humans.
The primary viremia seeds target organs which replicate virus and serve as a source of virus for release in the circulation. Virus can then enter the neural tissue causing encephalitis. The symptoms of arbovirus infection usually have an abrupt onset. The incubation period can vary from 3 to 21 days. Sequelae of encephalitis can be severe.