Michael S Doyle

Centers for Disease Control and Prevention, Druid Hills, GA, United States

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Publications (4)8.2 Total impact

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    ABSTRACT: Vector competence studies for West Nile virus (WNV) were conducted for two Culex (Culex) restuans Theobald populations Edison Park (EP) and Illinois Medical District (IMD), in Chicago, IL. The aim was to determine if there were differences between mosquito populations that contributed to the observed differences in the prevalence of WNV. Percentages of orally infected, disseminated, and transmitting mosquitoes were estimated using a generalized linear mixed effects model including a random effect for family to account for anticipated within-family correlation. Analysis indicated that percentages of infected, disseminated, and transmitting mosquitoes were not significantly different between EP and IMD. The within-family correlation was 0.46 (95% CI 0.28, 0.67), indicating reasonably strong tendency for WNV titers of bodies, saliva, and legs within families to be similar. Overall, our results show that vector competence of Cx. restuans for WNV is not a contributing factor to the observed differences in WNV human cases between the EP and IMD areas of Chicago.
    Journal of Medical Entomology 05/2012; 49(3):678-86. · 1.86 Impact Factor
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    ABSTRACT: Mosquitoes such as those in the Culex pipiens complex are important vectors of disease. This study was conducted to genetically characterize Cx. pipiens complex populations in the state of Colorado, USA, and to determine the number of genetic clusters represented by the data. Thirteen populations located among four major river basins were sampled (nā€Š=ā€Š597 individuals) using a panel of 14 microsatellites. The lowest-elevation sites had the highest Expected Heterozygosity (H(E)) values (range 0.54-0.65). AMOVA results indicated the presence of statistically significant amounts of variation within each level when populations were analyzed as one group or when they were grouped either by river basin or by their position on the east or west side of the Rocky Mountains. Most pairwise F(ST) values were significant via permutation test (range 0-0.10), with the highest values from comparisons with Lamar, in southeast CO. A neighbor joining tree based on Cavalli-Sforza and Edwards's chord distances was consistent with the geographic locations of populations, as well as with the AMOVA results. There was a significant isolation by distance effect, and the cluster analysis resolved five groups. Individuals were also assayed with an additional microsatellite marker, Cxpq78, proposed to be monomorphic in Cx. pipiens but polymorphic in the closely related but biologically distinct species Cx. quinquefasciatus. Low frequencies (ā‰¤3%) of Cx. quinquefasciatus alleles for this marker were noted, and mostly confined to populations along the Interstate 25 corridor. Pueblo was distinct in that it had 10% Cx. quinquefasciatus alleles, mostly of one allele size. The degree of population genetic structure observed in this study is in contrast with that of Cx. tarsalis, the other major vector of WNV in the western U.S., and likely reflects the two species' different dispersal strategies.
    PLoS ONE 01/2012; 7(10):e47602. · 3.73 Impact Factor
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    ABSTRACT: Early identification of increasing mosquito activity is critical to effective mosquito control, particularly when increasing host-seeking behavior may be associated with increased risk of mosquito-borne disease. In this paper, we analyzed the temporal abundance pattern of the West Nile Virus vector, Culex tarsalis, in Fort Collins, CO, using an autoregressive integrated moving average model. We determined that an autoregressive model order 5 with lagged minimum temperatures was best at describing the seasonal abundance of Cx. tarsalis. We then tested the effect of using both temporal and spatial subsets of the data to determine the effect of reduced sampling effort on abundance predictions. We found that, if reduced trapping is necessary due to limited resources, removal of the least productive 1/3 or 1/4 of the traps produced the least erroneous predictions of seasonality represented in the observed data. We show that this productivity-based subset scheme performs better than other sampling effort reductions in generating the best estimate of Cx. tarsalis abundance per trap-night.
    Journal of the American Mosquito Control Association 06/2011; 27(2):120-8. · 0.76 Impact Factor
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    ABSTRACT: In 2006-2007, stable flies, Stomoxys calcitrans (L.) (Diptera: Muscidae), were suspected of being enzootic vectors of West Nile virus (family Flaviviridae, genus Flavivirus, WNV) during a die-off of American white pelicans (Pelecanus erythrorhynchos Gmelin) (Pelecanidae) in Montana, USA. WNV-positive stable flies were observed feeding en masse on incapacitated, WNV-positive pelicans, arousing suspicions that the flies could have been involved in WNV transmission among pelicans, and perhaps to livestock and humans. We assessed biological transmission by infecting stable flies intrathoracically with WNV and testing them at 2-d intervals over 20 d. Infectious WNV was detected in fly bodies in decreasing amounts over time for only the first 6 d postinfection, an indication that WNV did not replicate within fly tissues and that stable flies cannot biologically transmit WNV. We assessed mechanical transmission using a novel technique. Specifically, we fed WNV-infected blood to individual flies by using a cotton swab (i.e., artificial donor), and at intervals of 1 min-24 h, we allowed flies to refeed on a different swab saturated with WNV-negative blood (i.e., artificial recipient). Flies mechanically transmitted viable WNV from donor to recipient swabs for up to 6 h postinfection, with the majority of the transmission events occurring within the first hour. Flies mechanically transmitted WNV RNA to recipient swabs for up to 24 h, mostly within the first 6 h. Given its predilection to feed multiple times when disturbed, these findings support the possibility that the stable fly could mechanically transmit WNV.
    Journal of Medical Entomology 05/2011; 48(3):656-68. · 1.86 Impact Factor