La Crosse Encephalitis Virus Infection in Field-CollectedAedes albopictus,Aedes japonicus, andAedes triseriatusin Tennessee

Abstract

La Crosse virus (LACV) is a mosquito-borne virus and a major cause of pediatric encephalitis in the USA. La Crosse virus emerged in Tennessee and other states in the Appalachian region in 1997. We investigated LACV infection rates and seasonal abundances of the native mosquito vector, Aedes triseriatus, and 2 recently introduced mosquito species, Ae. albopictus and Ae. japonicus, in an emerging disease focus in Tennessee. Mosquitoes were collected using multiple trapping methods specific for Aedes mosquitoes at recent human case sites. Mosquito pools were tested via reverse transcriptase-polymerase chain reaction (RT-PCR) of the S segment to detect multiple Bunyamwera and California serogroup viruses, including LACV, as well as real-time RT-PCR of the M segment. A total of 54 mosquito pools were positive, including wild-caught adult females and laboratory-reared adults, demonstrating transovarial transmission in all 3 species. Maximum likelihood estimates (per 1,000 mosquitoes) were 2.72 for Ae. triseriatus, 3.01 for Ae. albopictus, and 0.63 for Ae. japonicus. We conclude that Ae. triseriatus and Ae. albopictus are important LACV vectors and that Ae. japonicus also may be involved in virus maintenance and transmission.

Epidemiology of La Crosse Virus Emergence, Appalachia Region, United States

“…Given that transmission studies can be highly variable and that, since introduction of the tiger mosquito into the United States, local LACV strains may have adapted to be more suitable in this new host, it is also possible that our estimates for tiger mosquito competence are overly low (see Conditions Under Which Tiger Mosquitoes Enable LAC Spread, at http://www.clfs.umd.edu/biology/faganlab/disease-ecology.html). Recent evidence finding substantial infection rates in a tiger mosquito population in Tennessee ( 33 ) supports this conclusion, although further transmission studies and analyses of virus evolution are warranted.…”

Evaluating Surveillance Methods for Arboviral Vectors of La Crosse Virus and West Nile Virus of Southern Appalachia

“…albopictus and Ae. japonicus has likely expanded the distribution of LACV from the rural environment to the urban and suburban environment as both species have been recovered in field collections as infected with LACV (Gerhardt et al 2001, Harris et al 2015, Westby et al 2015. Previous surveillance studies have suggested a change in the composition of Ae.…”

“…triseriatus and Ae. albopictus, which may be due to the use of different trapping methods or could indicate a change in the ratio of these vector species (Westby et al 2015). Continued monitoring of these species and evaluation of different trapping methods are necessary for answering those questions.…”

“…triseriatus, and Ae. japonicus (Westby et al 2015). In 2012, Union County, TN, had a fatal case of La Crosse encephalitis that led to an in-depth vector ecology study comparing trapping sites and LACV strains (Lambert et al 2015).…”

“…albopictus (Skuse) and Ae. japonicus (Theobald) act as secondary LACV vectors (Watts et al 1973, Gerhardt et al 2001, Bevins 2007, Westby et al 2015. West Nile virus is transmitted by Culex mosquitoes, especially members of the Cx.…”