Final answer:
Japanese encephalitis virus (JEV) is the most common agent of severe viral encephalitis. It is transmitted to humans by Culex mosquitoes and has pigs and wading birds as biological reservoirs.
Step-by-step explanation:
The most common agent of severe viral encephalitis is Japanese encephalitis virus (JEV). JEV is transmitted to humans by Culex mosquitoes, usually the species C. tritaeniorhynchus.
The biological reservoirs for JEV include pigs and wading birds. Most patients with JEV infections are asymptomatic, with symptoms occurring in fewer than 1% of infected individuals.