According to the epidemiological data, Japanese encephalitis transmission season in Taiwan occurs between May and October. The peak season is June to July. Previous statistics collected over the past decade by Taiwan Centers for Disease Control (Taiwan CDC) indicate that most confirmed Japanese encephalitis cases experienced onset during May to October. Besides the first confirmed case of Japanese encephalitis in Taiwan that experienced onset in June in 1990, approximately 3% to 39% of the confirmed Japanese encephalitis cases during 1998 and 2007 experienced onset in May, and 25% to 94% of the confirmed cases experienced onset in June and July. Nevertheless, sporadic cases had occurred between August and October during 1998 and 2007. Therefore, Taiwan CDC warns people that this year’s Japanese encephalitis transmission season is about to begin.

As of April 18, 2008, 56 human cases of Japanese encephalitis have been reported. Of which, none has been confirmed. In 2007, the first human case of Japanese encephalitis was confirmed in early May.

The incubation period for Japanese encephalitis is 5 to 15 days. While the majority of infections are asymptomatic or with mild symptoms such as headache, fever or aseptic meningitis, more severe infection is marked by headache, high fever, coma and convulsion, and might lead to mental sequelae or even death.

In Taiwan, Japanese encephalitis is mainly spread by the infected Culex tritaeniorhynchus and Culex annulus mosquitoes. Swine are the amplifying hosts. The vectors’ favorite breeding sites include rice paddies, irrigation trenches, wet grasslands and large containers.

Japanese encephalitis vaccine has been proven effective in preventing the disease. Every year, vaccination is primarily available from March to May, but can be extended through September. A 15-month toddler should be vaccinated 2 doses given two weeks apart. A booster dose should be given one year after the 2-dose basal vaccination. A second booster should be administered when the child attends first grade at elementary school. Taiwan CDC urges parents to have their children vaccinated against Japanese encephalitis on time. To prevent infection, avoid visiting vector-breeding sites such as pigpens at dawn and dusk when mosquitoes are most active. When needing to visit mosquito-prone places, people are advised to wear long-sleeved shirts and long pants, and apply mosquito repellent to exposed body parts. To further prevent mosquito bites and lower the risk of contracting Japanese encephalitis, use mosquito net when sleeping.