It is a disease spread to humans by the mosquitoes of the Culex genus and is caused by a virus belonging to the Flavivirus genus (to which the viruses responsible for dengue and yellow fever also belong).
Humans are infected by bites from infected mosquitoes. Culex mosquitoes bite in the hours of darkness and semi-darkness and their sting is very painful. These mosquitoes spawn in flooded rice paddies, swamps, or small water basins.
Symptoms and complications
Most infections are asymptomatic; the actual encephalitis manifests in percentages varying from 1 to 20 cases for every thousand infections, with the appearance of headache, fever, convulsions, neurological disorders, impaired consciousness and coma.
Almost 20-30% of the subjects who develop encephalitis die, and almost 50% of the survivors have severe permanent neurological sequelae such as spastic tetraparesis, hemiplegia, severe cognitive deficits and difficulty swallowing.
Impact on the population
There are around 50,000 cases of Japanese encephalitis worldwide every year and approximately 10,000 deaths. The most affected areas are rural areas (in particular rice-growing zones) in East Asia, from the Indian Sub-continent to the Philippines and Japan, and part of Oceania (Pacific Islands). In recent years, the infection has also affected other countries such as India, Nepal and Sri Lanka; international travel and animal trade could potentially carry it to other areas. Most cases occur from May to September (when the vectors are most active); this is typical in temperate and subtropical zones, while in tropical areas the pathology is endemic and strikes in all seasons. In endemic countries, immunity increases with age: the pathology tends to affect more people aged <15 years.
Sources / Bibliography
- Modern Infectious Disease Epidemiology - (A. Krämer, M. Kretzschmar, K. Krickeberg;)
- Manuale per il Controllo delle Malattie Trasmissibili - (Rapporto ufficiale dell'APHA - D. L. Heymann)
- Encyclopedia of Virology - 3rd Ed. - (B.W.J. Mahy, M.H.V. Van Regenmortel et al.)
- Virology: Principles and Practice - (J. Carter, V. Saunders et al.)
- Foundations in Microbiology - 8th Ed. - (K. P. Talaro, B. Chess et al.)
- Vaccini e vaccinazioni - 3rd Ed. - (G. Bartolozzi et al.)
- Harrison's Principles of Internal Medicine - 16th Ed. - (Kasper, Braunwald, Fauci. Longo et al.).
- Infectious Diseases and Arthropods - 2nd Ed. – (J. Goddard)