The epidemiologic triad (epi-triad) classically consists of agent, host, and environment. However, with vector-borne diseases (arthropod-transmitted pathogens), the vector plays a vital role, and without the vector there is no sustained pathogen transmission. By not emphasizing the importance of the arthropod vector, the role of the vector is often neglected or underappreciated. The complexities of vector-borne diseases are reviewed by describing the ecology and transmission of the Japanese encephalitis virus (JEV), the causative agent of Japanese encephalitis (JE). JE is a mosquito-borne zoonosis that affects most countries in South and Southeast Asia, and the Western Pacific Rim. It is considered the main cause of viral encephalitis in that region, affecting mainly children up to 14 yr old. The virus is transmitted by mosquitoes, particularly of the Culex genus, and the transmission cycle is complex, involving pigs and ardeid birds as reservoir hosts. Environmental, ecological, and social determinants play a paramount role on the epidemiology of JE and JEV, as well as on its geographical expansion over new territories. JE has no cure; thus, efforts are put forth towards prevention and control by reducing exposure to potentially infected mosquitoes, or vaccination. The sections below cover the most important aspects of JE and JEV, providing a summary of the current body of knowledge and placing the complicated transmission cycle in context of a new epi-triad.