Japanese Encephalitis Virus (JEV) is an emerging arbovirus related to Dengue, West Nile and Yellow Fever viruses.  There is an estimated 50,000-175,000 cases per annum and 3 billion people are at risk of infection [1].  JEV is currently not present in the Americas and is endemic in 24 countries in the Western Pacific and SE Asian regions [1, 2].  Most symptoms are mild or asymptomatic.  Around 1 in 250 cases are severe which involves rapid onset of fever, headache, seizures, coma and ultimately death.  Symptoms develop typically between 5-15 days post infection [1]. There are safe and effective vaccines available for JE but there is currently no antiviral cure – treatment involves relieving symptoms [1].  Culex tritaeniorhynchus is the main vector for JEV in Asia.  The mosquito’s ecology and ability to feed on both sylvatic and human hosts is an important aspect when considering epidemiology and disease control.  The transmission cycle involves three hosts: human, pigs and Ardeid birds (cranes, herons, egrets).  The virus normally exists in an enzootic cycle (circulating between mosquito-bird-mosquito-pig) with pigs acting as an amplifying host as they can hold higher numbers of virions (virus particles) and therefore amplify the virus in the mosquito.  Zoonotic transmission (when humans become infected) occurs as ‘spillover’ from the main cycle and hence; humans are a dead-end host [2, 3, 4].  Irrigated rice paddies provide the perfect setting as the mosquito can breed in the standing water and migratory water birds are attracted to these areas also to breed.  Because of heavy use of pesticides in these paddy fields, C. tritaeniorhynchus has developed insecticide resistance [3, 5].


  1. World Health Organisation. Japanese Encephalitis Factsheet. 2019. Available at http://www.who.int/mediacentre/factsheets/fs386/en/

  2. Lord JS, Gurley ES, Pulliam JR. Rethinking Japanese encephalitis virus transmission: a framework for implicating host and vector species. PLoS neglected tropical diseases. 2015 Dec 10;9(12):e0004074. http://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0004074

  3. Jeffries CL, Walker T. The potential use of Wolbachia-based mosquito biocontrol strategies for Japanese encephalitis. PLoS neglected tropical diseases. 2015 Jun 18;9(6):e0003576. https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0003576

  4. Ricklin ME, García-Nicolás O, Brechbühl D, Python S, Zumkehr B, Nougairede A, Charrel RN, Posthaus H, Oevermann A, Summerfield A. Vector-free transmission and persistence of Japanese encephalitis virus in pigs. Nature communications. 2016 Feb 23;7:10832. https://www.nature.com/articles/ncomms10832

  5. Saha P, Ballav S, Chatterjee M, Ganguly S, Sarker M, Biswas AK, Pramanik T, Basu N, Maji AK. The status of susceptibility of Japanese encephalitis vectors to insecticides in endemic areas of northern districts of West Bengal, India. Japanese journal of infectious diseases. 2018;71(2):91-8. https://www.jstage.jst.go.jp/article/yoken/71/2/71_JJID.2017.465/_article/-char/ja/