Persistence of La Crosse virus (California encephalitis serogroup) in north-central Illinois
Clark, G.G.; Pretula, H.L.; Rohrer, W.H.; Harroff, R.N.; Jakubowski, T.
American Journal of Tropical Medicine and Hygiene 32(1): 175-184
1983
ISSN/ISBN: 0002-9637 PMID: 6824122 Document Number: 210534
La Crosse (LAC) virus was first isolated in Illinois [USA] from a pool of 50 female Aedes triseriatus mosquitoes collected in July 1976, in Peoria Heights. From 1978 through 1981, 27 strains (11 from males and 16 from females) of LAC virus were recovered from 888 pools containing 22,021 adult A. triseriatus mosquitoes from the same study area. These mosquitoes had developed from larvae and pupae collected from 50 individually identified treeholes. Of the 14 trees that yielded LAC virus-positive mosquitoes, 1 was positive in 3 of 4 yr and another was positive in all 4 yr. The latter tree had minimum mosquito field infection rates (MFIR) ranging from 3.4 to 12.7/1,000. Eight (57%) of the trees with positive mosquitoes were red oak (Quercus rubra) while 10 (71%) were in the oak genus (Quercus). The 4 most productive treeholes accounted for 30% of mosquitoes tested and 52% of the LAC isolations. In 1979, 6729 A. triseriatus mosquitoes were collected in man-baits and tested for virus. From 1282 tested in 259 pools (.hivin.x = 5), 13 LAC isolates were made, resulting in a field infection rate (FIR) of 11.4/1,000. The remaining 5447 were tested in 218 pools (.hivin.x = 25) and 48 strains of LAC were isolated for a FIR of 9.9/1,000. The relationship of these findings to the occurrence of human LAC encephalitis cases in Peoria County, Illinois is discussed. Repeated recovery of virus from this study area reflects a stable, yet dynamic, focus of LAC virus transmission.