West Nile virus is a mosquito-borne infection that can cause encephalitis. In 2008, three mosquitoes trapped in Wilton tested positive for the disease, as did mosquitoes in neighboring towns. Mosquitoes can reproduce in any stagnant water that lasts more than four days. People can best protect themselves by eliminating any such pools of stagnant water around their home, such as birdbaths, old tires, kiddy pools, and clogged gutters. Minimize outdoor activities between dusk and dawn. Consider the use of mosquito repellent.

Viral encephalitis may not have any symptoms at all; mild cases may include a slight fever and/or headache. Severe infections are marked by a rapid onset of high fever, head and body aches, and usually occur five to 15 days after exposure. There is no specific treatment for viral infections, other than to treat the symptoms and provide supportive care. Those who may be most susceptible to encephalitis are infants, the elderly and people with damaged immune systems.