D3030: Searching for La Crosse virus in La Crosse mosquito populations

La Crosse virus (LACV) is a mosquito-borne arbovirus that can cause devastating pediatric encephalitis. The first human case of LACV was described in 1964 in La Crosse WI, USA. In response, the La Crosse County Health Department initiated surveillance and mosquito control in 1978; that program ended in 2017 due to a dramatic decline in diagnosed cases of the disease. We postulated that the decline in cases could be related to (1) successful control of the vector species in the area, (2) a change in the virus associated with more asymptomatic infections, or (3) a decline in the prevalence of the virus within mosquito populations. In 2021, I returned to historical case sites to survey for the primary vector species, Aedes (Ochlerotatus) triseriatus. I collected mosquito eggs via oviposition traps fitted with seed germination papers in the counties of La Crosse and Trempealeau, WI USA. We hatched eggs and reared larvae to adulthood for identification and testing. In total, 20,020 mosquitoes were identified. Ae. triseriatus was by far the most common mosquito collected in these traps with Ae. hendersoni and Ae. japonicus also observed. Ae. triseriatus specimens were subjected to RNA extraction and tested for LACV via RT-PCR to determine the prevalence of LACV in Ae. triseriatus populations.