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Browsing by Author "Black, William C., IV, advisor"

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    Aedes aegypti and dengue virus investigation of anatomic, genomic, and molecular determinants of vector competence
    (Colorado State University. Libraries, 2009) Bernhardt, Scott Arthur, author; Blair, Carol D., advisor; Black, William C., IV, advisor
    Dengue (DENV) causes one of the most rapidly expanding diseases in the tropics. Vector competence (VC) in Aedes aegypti for DENV-2 is a quantitative trait and has been shown to be highly variable. Questions remain as to whether variation in VC continues to exist after the primary field observation. What genetic factors contribute to VC and do these factors evolve from arbovirus exposure remain unclear.
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    DDT and pyrethroid resistance in Xenopsylla cheopis (Rothschild), the Oriental rat flea in northern Uganda
    (Colorado State University. Libraries, 2011) Ames, Abbe D., author; Black, William C., IV, advisor; Gage, Kenneth L., advisor; McAllister, Janet C., committee member; Kondratieff, Boris C., committee member; Cole, Patricia A., committee member
    Development of insecticide resistance by vectors of disease is a well-recognized and continuous concern for public health officials. Monitoring insects for development of resistance to the chosen toxicants is part of effective management philosophy. Several programs to control mosquito vectors of malaria utilize insecticides with similar modes of action targeting the insect. Fleas can vector plague and in many areas inhabit the same environment that is the focus of mosquito management. Non-target insect development of resistance is a phenomenon most commonly associated with agriculture, but can also apply to insect vectors that threaten public health. Rapid and effective methods of monitoring for the possible development of insecticide resistance in fleas are important measures taken to prevent or suppress a plague outbreak. This study describes the development and application of a new field assay for evaluating phenotypic demonstration of insecticide resistance in fleas, results of biochemical analyses performed to evaluate possible development of metabolic detoxification pathways, and the subsequent elucidation of the para voltage gated sodium channel gene in Xenopsylla cheopis (Rothschild) with concurrent analyses of the prevalence and effects of knockdown (kdr) mutations in the gene. The field assay used a glass Petri dish coated with a dose of a chosen insecticide and a time mortality assay that was performed for 60 minutes. Discriminating concentrations, established on colony reared fleas, was tested on field collected fleas in northern Uganda. Fleas from villages with a history of indoor residual spraying (IRS) of DDT and /or pyrethroid were tested with those insecticides and significant increased survival was demonstrated. Phenotypic resistance to DDT was demonstrated with an 81.8% survivorship. Lambda-cyhalothrin tested fleas from three villages demonstrated phenotypic resistance of levels of 57.7%, 60.5%, and 58% survivorship. Enzyme profiles indicated increased levels of expression of α-esterase and β-esterase in field caught fleas compared to colony-reared fleas. Fleas potentially exposed to DDT and/or pyrethroids had higher levels than did unexposed fleas. An increase in insensitive acetylcholinesterase was found in fleas from villages with no known history of IRS. No increase in glutathione S-transferase was noted in any population. The para voltage gated sodium channel gene for X. cheopis was amplified and sequences for colony and Ugandan fleas were analyzed with emphasis on knockdown resistance (kdr) evolution in the fleas. Extensive evidences of selective pressures influencing genetic profiles of kdr development faster than expected for random mutation or recombination were found. The phenylalanine allele, associated with kdr, was found at an average of 95.1% frequency in villages with an IRS history. Field caught fleas with no known insecticide exposure had an allele frequency of 13.3%. All three studies clearly indicate resistance is developing quickly in Ugandan flea populations and should be addressed with surveillance and management.
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    Mexican mosquitoes: overcoming barriers for dengue and Zika virus infection
    (Colorado State University. Libraries, 2017) Garcia Luna, Selene M., author; Black, William C., IV, advisor; Ebel, Gregory D., committee member; Perera, Rushika, committee member; Hess, Ann M., committee member
    The mosquito transmitted arboviruses cause an important burden of disease worldwide. In Latin America dengue disease is endemic with more than 1 million dengue fever cases reported yearly. In addition to dengue, chikungunya and Zika viruses have been also circulating since their introduction in 2014 and 2015 respectively. For a mosquito-borne infection to occur susceptible humans, the mosquito vector and the virus should coincide. This dissertation was focused in the mosquito vector and its ability to acquire, maintain and then transmit the virus, termed vector competence. The vector competence was a fundamental measure for the research chapters in which we studied different aspects on the interactions between Aedes aegypti and Aedes albopictus mosquitoes and Dengue-2 and Zika viruses. This dissertation includes three research chapters which were based on the following specific aims. Specific aim 1: Determine the patterns of gene flow and vector competence for DENV-2 of Aedes aegypti from around the Mexican Neovolcanic Axis. It was previously reported that the intersection of the Neovolcanic axis (NVA) with the Gulf of Mexico coast in the state of Veracruz acts as a discrete barrier to gene flow among Ae. aegypti populations north and south of the NVA. These collections also differed in their vector competence (VC) for Dengue virus serotype 2 (DENV-2). Therefore, the goal of the present study was to determine if the same patterns remained 8 years later in collections from 2012. For which haplotype variation for the mitochondrial ND4 and the nuclear genes Dicer-2 and Argonaute-2 was analyzed for north and south of the NVA mosquito populations. Also, the VC of those populations for DENV-2 was determined (Chapter 2). Specific aim 2: Profile the microRNA response of Aedes aegypti midguts to DENV-2 exposure and DENV-2 infection. The microRNA pathway has been found to modulate important physiological mechanisms in mosquito vectors. Therefore in the context of DENV infection, miRNA modulation may provide information about key genes that are important for infection. Differential expression patterns of miRNAs from mosquito midguts upon infection have been unexplored. Therefore, we explored on the involvement of the miRNA pathway in persistently DENV-2 infected mosquitoes, for which DENV-2 virus was detected at 14 days post-infection (dpi). Two comparisons were included in the study. In the first group, DENV-2 infected midguts that produced a disseminated infection (did not have a midgut escape barrier) were contrasted with those that were given a non-infectious blood meal. Also, we included a comparison group from a subset of mosquitoes from the same cohort that were exposed to DENV-2 regardless of their midgut infection status contrasted to unexposed mosquitoes. Analysis of miRNA regulation in mosquitoes may help us to understand more about the intricate interactions between the virus and the vector host (Chapter 3). Specific aim 3: Assess the variation in competence for Zika virus transmission by Aedes aegypti and Aedes albopictus from Mexico. Previous studies have reported low Zika virus (ZIKV) transmission rates for the Asian lineage of ZIKV using mosquitoes from a wide geographical range from the Americas. Beside low transmission rates we hypothesized that VC is variable and is highly dependent upon the geographic origin of the mosquito populations. Hence, we analyzed the ZIKV transmission potential of recently colonized Aedes collections. Ten Ae. aegypti and three Ae. albopictus collections from different locations across Mexico were analyzed for ZIKV (strain PRVABC59 Asian genotype) vector competence at 7 and 14 dpi. We calculated the additive contribution of each of the four transmission barriers to ZIKV infection. In addition, we evaluated the contribution of both mosquito species to ZIKV transmission in areas where their distributions overlap (Chapter 4).
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    Phylogeny of selected species of subgenus Culex mosquitoes (Diptera: Culicidae) from the U.S., Puerto Rico, and Guatemala, based on nucleotide sequences from three genes
    (Colorado State University. Libraries, 2009) Deus, Stephen, author; Black, William C., IV, advisor
    Phylogeny was inferred for subgenus Culex mosquitoes from the United States, Guatemala and Puerto Rico based on aligned nucleotide sequences from three genetic regions: 705 base pairs (bp) of the mitochondrial cytochrome oxidase subunit II (COII) gene, a region of ribosomal DNA containing internal transcribed spacers (ITS) 1 and 2, and 850 bp of the nuclear protein-coding white gene. Each gene was evaluated for its utility in phylogenetic inference, as were four methods of phylogenetic analysis: neighbor-joining distance, parsimony, maximum likelihood, and Bayesian analysis. A simultaneous analysis of the COII and ITS data was performed using the Bayesian method. The phylogeny challenges the monophyly of subgenus Culex and helps clarify the phylogenetic positions of subgenus Phenacomyia and genus Deinocerites relative to subgenus Culex.
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    Population genetics and vector competence of Aedes aegypti in West Africa
    (Colorado State University. Libraries, 2014) Dickson, Laura B., author; Black, William C., IV, advisor; Miller, Barry, committee member; Foy, Brian, committee member; Blair, Carol, committee member; Huyvaert, Kate, committee member
    The mosquito, Ae. aegypti is the primary vector for all four serotypes of dengue (DENV 1-4) and yellow fever viruses worldwide. Dengue remains an important public health problem with an estimated 390 million cases per year and yellow fever outbreaks are still continuously reported even though a safe and effective vaccine exists. Aedes aegypti (L) is found globally in tropical and sub-tropical climates and exists as two subspecies: Ae. aegypti aegypti (Aaa) and Ae. aegypti formosus (Aaf) which have previously been defined by the presence or absence of scales on the first abdominal tergite. This classification system was developed in East Africa and is contradictory in West Africa where this mosquito is genetically diverse and exhibits great variation in susceptibility to DENV and YFV, which is a quantitative genetic trait. Understanding the population genetics, the vector competence, and the way in which genetic diversity contribute to vector competence of Ae. aegypti can improve our general understanding of mosquito/virus interactions and lead to potential ways to control these mosquitoes in nature. In this dissertation, the distribution of FST values calculated from deep sequencing data between mosquitoes from two diverse locations in Senegal, one location in Mexico, and one location in Thailand across the entire genome were compared to identify the degree of genomic divergence as well as identify genes involved in speciation between the various populations. The distribution of FST values were also compared in different gene regions and mutation types to identify which parts of the genome provide the greatest resolution of subspecies population structure. Genetic crossing experiments and deep sequencing of the sex determining locus of Ae. aegypti from Senegal and Thailand was used to demonstrate discrete genetic differences between the subspecies. The vector competence for a local sylvatic isolate of DENV-2 and two genetically diverse YFV isolates was compared between various collections of Ae. aegypti throughout Senegal to demonstrate that vector competence in these mosquitoes is dependent on the viral isolate. The genetic diversity of an important immune sensing gene, Dcr2 of the exo-siRNA pathway, was determined from mosquitoes with various vector competence phenotypes to test how the genetic diversity of this gene in individuals and populations of mosquitoes contribute to vector competence. Overall, data in this dissertation suggest 1) allopatric speciation between Ae. aegypti from Senegal and Mexico or Thailand, and sympatric speciation within Senegal based on the distributions of FST values and variations in the sex determining locus between populations, 2) vector competence of Ae. aegypti from Senegal is dependent on the flavivirus species and viral genotype, and 3) increased genetic diversity of Dcr2 in individual Ae. aegypti, but not from populations of Ae. aegypti, from Senegal is correlated with the ability of Ae. aegypti to control DENV-2 infection. These results aid in our general understanding of the role of genomic divergence in speciation, as well as our understanding of genetics, vector competence, and the genetics of vector competence of West African Ae. aegypti, which could provide insight into the way we identify subspecies and make predictions about vector competence in this region.