Comparison of mosquito abundance, distribution and parity between a high and a low prevalence site for La Crosse encephalitis in Eastern Tennessee
A three-year investigation of the seasonal distribution, abundance and diversity of
mosquitoes at a high and a low prevalence area for La Crosse (LAC) encephalitis was
conducted in eastern Tennessee, USA. We identified a high LAC prevalence site (Knox
County) from which two cases of LAC encephalitis were confirmed, one in 1997 and the
other in 2000, and an ecologically similar low prevalence site (Blount County) with no
confirmed LAC cases. Mosquitoes were collected at each site using 2 Center for Disease
Control (CDC) miniature light traps baited with carbon dioxide, 1 Omni-directional Fay
trap baited with carbon dioxide, 2 gravid traps and 25 oviposition traps. At both sites,
mosquitoes were collected weekly between late May and early November 2003-2005.
The traps that attracted host-seeking and gravid adults were operated for a 24-hour time
period each week, while the oviposition traps were left out for the entire week.
Throughout the 2003, 2004, and 2005 collection periods, a total of 7,593 adult female
mosquitoes were collected and identified to species (Knox County (n=3,646), Blount
County (n=3,946)). Aedes albopictus, Ochlerotatus triseriatus, and Ae. vexans were the
most commonly collected mosquitoes at both sites. The proven and suspected LAC
vectors, Oc. triseriatus and Ae. albopictus, comprised 19.1% and 46.6% of all adult
female mosquitoes collected and identified, respectively. Ochlerotatus triseriatus was
collected most often in the early summer (June) with fewer numbers collected in the late
summer, whereas Ae. albopictus collections tended to be largest in the late summer to
early fall (August and September). In 2003, egg and adult collections fluctuated in a
similar manner between sites, but not among species. Aedes vexans comprised 26.6% of
all adult female mosquitoes collected in 2003, but only 8.3% and 14.5% in 2004 and
2005, respectively. There were no significant differences in egg or adult collections of
Ae. albopictus and Oc. triseriatus between the high and low prevalence LAC sites.
Weather patterns also appeared to be similar between the two sites. The total average
monthly parity rate for Ae. albopictus and Oc. triseriatus at each site was between 40-
48% parous in 2003, between 35-49% parous in 2004 and between 8-24% parous in
2005. Parity rates did not significantly differ between sites or species. The carbon
dioxide baited CDC light traps collected most of the adult mosquitoes used in parity
determination. Small mammals were sampled multiple times at each site with live traps.
Each site contained sufficient populations of squirrels for LAC virus amplification, but
no chipmunks were collected from the low prevalence area for LAC encephalitis. La
Crosse antibodies were found at both sites, but the Knox County site had a higher
prevalence of 2.65% compared to the Blount County site with a prevalence of 0.44%.
Out of a total of 226 serum samples tested from both sites, 5 squirrels and 2 chipmunks
tested positive for LAC antibodies.
School:The University of Tennessee at Chattanooga
School Location:USA - Tennessee
Source Type:Master's Thesis
Keywords:mosquitos encephalitis la crosse california group viruses tennessee
Date of Publication: