Japanese Encephalitis: A Persistent Threat

Japanese encephalitis virus (JEV) belongs to arthropod-borne virus family, which are infectious agents transmitted by blood-sucking arthropods. They multiply in the tissues of the arthropod without evidence of disease or damage. The principal vector is Culex mosquito, most important being C. tritaenorhynchus, which is a rural mosquito, breeding extensively in rice fields and bites large domestic animals. In temperate zones, this vector is present in greatest density from June to November. The natural cycle of JEV consists of pig–mosquito–pig or bird–mosquito–bird cycle. Pigs serve as most important biological amplifiers and reservoirs. JEV is transmitted to humans through the bites of infected mosquitoes. Humans are accidental, dead-end hosts as they do not develop a level of viraemia sufficient to infect mosquitoes. The infection with JEV ranges from nonspecific febrile illness to a severe meningoencephalomyelitis illness. The risk for Japanese encephalitis varies by local ecology and season. In temperate areas of Asia, human disease usually peaks in summer and falls down after that and these seasonal epidemics can be explosive with thousands of cases occurring over a period of several months; whereas, in the subtropics and tropics, transmission can occur throughout the year, with disease at a peak during rainy season. A detailed study has been done on geographic distribution of JEV and incidence and burden of disease in India. Vaccination proves to be the best measure to protect the individual against any disease. So, large scale immunization of susceptible human population is highly important to prevent this deadly infection. In India, vaccinations against Japanese encephalitis are administered in areas where the disease is hyperendemic.