Determining the Vector Competence of Culex Species Mosquitoes for Japanese Encephalitis Virus

Abstract

Japanese encephalitis virus (JEV) is an emerging mosquito-borne orthoflavivirus, transmitted through a zoonotic transmission cycle between Culex spp. mosquitoes and aquatic birds and pigs. The first major outbreak of JEV was reported in 1924 in Japan. Since then, JEV has spread throughout Asia and has become the number one cause for virus-induced encephalitis. In 2022 JEV spread to a new continent and became endemic to Australia causing widespread concern of the same occurring to North America. There are currently five known genotypes of JEV, differentiated by the sequence of their envelope protein. Of these five genotypes, GIII has been historically the most prevalent, with GI taking over in more recent years. GII and GIV have been less prevalent and therefore less studied; however, GIV was the genotype that emerged in Australia, which has led to more concern over these less studied genotypes. Previous studies have found that many species of Culex mosquitos from Asia are competent vectors for JEV. To further investigate the risk of JEV spread into North America, vector competence of three North American Culex species mosquitoes were investigated. The three mosquito species utilized in this study were Culex pipiens, Culex quinquefasciatus, and Culex tarsalis, as these are the three main vectors for a similar flavivirus, West Nile virus which also emerged in North America. To test their competency as vectors, we utilized an artificial blood meal spiked with four genotypes of JEV (GI to GIV). After fourteen days, mosquitos were dissected, and the bodies, legs and wings, and saliva were collected for analyzing infection, dissemination, and transmission rates. We determined that across our three species all genotypes of JEV were able to be transmitted. This thesis provides insights into JEV, its impacts on human health and agriculture, its disease presentation in animal hosts, and its enzootic cycle. Furthermore, this thesis indicates the increasing and plausible risk of JEV emergence into North America.