Environmental conditions for Jamestown Canyon virus correlated with population-level resource selection by white-tailed deer in a suburban landscape.

Suburban landscapes can alter spatial patterns by white-tailed deer (Odocoileus virginianus) and increase animal contact with vectors, pathogens, and humans. Close-contact relationships at a landscape level can have broad implications for disease epidemiology. From 1995-1999, we captured and radio-collared 41 deer in two suburban forest preserves in Chicago, Illinois. We collected blood to determine if animals were seronegative or seropositive for Jamestown Canyon virus and tracked deer movements within suburban habitats. We developed utilization distributions at the population-level and evaluated resource selection for seronegative and seropositive deer. We used maximum likelihood estimation for model selection via Akaike information criterion and then restricted maximum likelihood estimation to attain unbiased estimates of the parameters in the top-ranking models. The top-ranking model describing the resource selection of seronegative deer received almost the full weight of evidence (Akaike information criterion ωi = 0.93), and included the proportion of wetlands, precipitation in year t, and an interaction of the proportion of wetlands and precipitation in year t. The top-ranking model describing resource selection of seropositive deer received the full weight of evidence (Akaike information criterion ωi = 1.00). The model included distance to nearest populated place, distance to nearest river, length of road in each grid cell, precipitation in year t, and an interaction of the length of road in each grid cell and precipitation in year t. These results are valuable for mapping the spatial configuration of hotspots for Jamestown Canyon virus and could be used to educate local residents and recreationalists to reduce human exposure.

Evaluation of the eastern cottontail Sylvilagus floridanus as an amplifying vertebrate host for Cache Valley virus (Bunyaviridae) in Indiana.

To evaluate the importance of eastern cottontails (Sylvilagus floridanus) as amplifying hosts for Cache Valley virus (CVV), we tested hunter-provided blood samples from northern Indiana for specific neutralizing (N) antibodies against this mosquito-borne bunya-virus. Samples were collected during the winter of 1994-95. Two seronegative eastern cottontails, captured in July 1995, were also infected with CVV by subcutaneous inoculation, and two others were infected by allowing CVV-infected mosquitoes to feed on them. The results indicate that eastern cottontails probably are not important amplifying hosts for CVV. The prevalence of N antibodies against CVV was low (6.0%, n=82) among the hunter-killed animals. Low viremia (<1.8 log10 plaque-forming units/ml) of short duration (1-3 days) were seen in three of four experimentally infected eastern cottontails. The viremias were insufficient for infecting Coquillettidia perturbans, a mosquito species commonly found naturally infected with CVV.

Identification of quantitative trait loci for larval morphological traits in interspecific hybrids of Ochlerotatus triseriatus and Ochlerotatus hendersoni (Diptera: Culicidae).

Ochlerotatus triseriatus is the natural vector of La Crosse virus, a common cause of pediatric encephalitis in the United States; the closely related Ochlerotatus hendersoni transmits this virus at low frequency. Adults of these mosquito species are difficult to distinguish morphologically; however, the larval stages show species-specific differences in several characters. We identified genomic regions contributing to the differences between the larvae of these species through interspecific hybridizations. Quantitative trait loci (QTL) were identified by standard interval mapping techniques and by univariate marker association analyses. We examined 159 F(2) progeny from an Oc. hendersoni female by Oc. triseriatus male interspecific cross for variation in the number of saddle and siphon hair branches, attachment of the acus, and morphology of the anal papillae. At least one putative QTL was identified for each of the phenotypes examined. QTL most commonly mapped to linkage group (LG) III, although QTL were identified on LGI and LGII for three phenotypes each. Several of these QTL, and particularly those on LGIII, also map to genome regions controlling adult female body size and ability to orally transmit La Crosse virus. Further studies are required to elucidate the relationships among these traits and the impact they may have had on the ecological specialization and speciation of these mosquitoes.

Quantitative genetics of vector competence for La Crosse virus and body size in Ochlerotatus hendersoni and Ochlerotatus triseriatus interspecific hybrids.

La Crosse virus is a leading cause of pediatric encephalitis in the United States. The mosquito Ochlerotatus triseriatus is an efficient vector for La Crosse virus, whereas the closely related O. hendersoni transmits only at very low rates. Quantitative trait loci (QTL) affecting the ability to orally transmit this virus and adult body size were identified in 164 F(2) female individuals from interspecific crosses of O. hendersoni females and O. triseriatus males using a combination of composite interval mapping (CIM), interval mapping (IM) for binary traits, and single-marker mapping. For oral transmission (OT), no genome locations exceeded the 95% experimentwise threshold for declaring a QTL using IM, but single-marker analysis identified four independent regions significantly associated with OT that we considered as tentative QTL. With two QTL, an increase in OT was associated with alleles from the refractory vector, O. hendersoni, and likely reflect epistatic interactions between genes that were uncovered by our interspecific crosses. For body size, two QTL were identified using CIM and a third tentative QTL was identified using single-marker analysis. The genome regions associated with body size also contain three QTL controlling OT, suggesting that these regions contain either single genes with pleiotropic effects or multiple linked genes independently determining each trait.

A preliminary characterization of the physiological ecology of overwintering Anopheles mosquitoes in the midwestern USA.

Field-collected Anopheles quadrimaculatus and An. punctipennis adult mosquitoes from various types of overwintering hibernacula in southwestern Michigan and northern Indiana were examined for cold tolerance. Adult mosquitoes were collected on a monthly basis from October 1997 to April 1998. The mean supercooling point for adult for An. punctipennis was significantly lower than that for An. quadrimaculatus. The lower lethal temperatures for these species were -17 degrees C and -15 degrees C for An. punctipennis and An. quadrimaculatus, respectively.