LaCrosse Encephalitis virus (LACV) is an arthropod-borne virus (arbovirus) that is currently found in the United States where it is a significant cause of neuroinvasive encephalites [1, 2].  Ohio, North Carolina and West Virginia have the greatest number of cases per year from 2007-2016 [3, 4].  An average of 63 neuroinvasive cases of LACV occured each year in the USA from 2007-2016 [1] but this number should be underestimated as there is under-reporting of less-severe cases.  LACV takes between 5-15 days post-infection to manifest into symptoms (this is the intrinsic incubation period).  The symptoms include typical encephalitis traits such as headache, nausea and lethargy.  Severe cases typically affect under 16 year olds but are rarely (<1%) fatal.  Neurological sequelae (medical complications as a consequence of the infection) have been reported including seizures and cognitive and neurological abnormalities [5]. The virus is currently known to be transmitted by four species - Aedes triseriatus, Ae. aegypti, Ae. albopictus and Aedes japonicus [6, 7].  It was shown that, like many arboviruses, the virus can survive adverse weather conditions by being transmitted from female mosquitoes to offspring in Ae. triseriatus (transovarial transmission) [8].  The virus was also demonstrated to be transmitted from males to females of Ae. triseriatus (venereal transmission) [9].


  1. Centers for Disease Control and Prevention. LaCrosse Encephalitis virus: Epidemiology. June 2019. Available at

  2. Haddow AD, Bixler D. The spatial epidemiology and clinical features of reported cases of La Crosse virus infection in West Virginia from 2003 to 2007. BMC infectious diseases. 2011 Dec;11(1):29.

  3. ArboNET, Centers for Disease Control and Prevention. LaCrosse virus neuroinvasive disease cases reported by state of residence, 2009-2018. June 2019.

  4. ArboNET Disease Maps. Accessed December 2018. Available at

  5. Centers for Disease Control and Prevention. LaCrosse Encephalitis virus: Symptoms. January 2019. Available at

  6. Bara JJ, Parker AT, Muturi EJ. Comparative susceptibility of Ochlerotatus japonicus, Ochlerotatus triseriatus, Aedes albopictus, and Aedes aegypti (Diptera: Culicidae) to La Crosse virus. Journal of medical entomology. 2016 Sep 7;53(6):1415-21.

  7. Westby KM, Fritzen C, Paulsen D, Poindexter S, Moncayo AC. La Crosse encephalitis virus infection in field-collected Aedes albopictus, Aedes japonicus, and Aedes triseriatus in Tennessee. Journal of the American Mosquito Control Association. 2015 Sep;31(3):233-41.

  8. Watts DM, Pantuwatana S, DeFoliart GR, Yuill TM, Thompson WH. Transovarial transmission of LaCrosse virus (California encephalitis group) in the mosquito, Aedes triseriatus. Science. 1973 Dec 14;182(4117):1140-1.

  9. Thompson WH, Beaty BJ. Venereal transmission of La Crosse (California encephalitis) arbovirus in Aedes triseriatus mosquitoes. Science. 1977 Apr 29;196(4289):530-1.