Browsing by Author "D. Wes Watson, Committee Member"

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    An Economic and Social Analysis of La Crosse Encephalitis in North Carolina
    (2002-11-04) Utz, John Todd; Charles S. Apperson, Committee Chair; V. Kerry Smith, Committee Member; J. Newt MacCormack, Committee Member; D. Wes Watson, Committee Member
    La Crosse encephalitis (LACE), a viral illness vectored by mosquitoes, is endemic in western North Carolina. Clinical manifestations of La Crosse (LAC) virus infection range from mild fever to aseptic meningitis or frank encephalitis. Due to non-specific or sub-clinical symptoms and the absence of an accurate, timely diagnostic tool, the true incidence of LAC virus infection is unknown for the endemic foci of the illness. To estimate the socioeconomic burden of LACE in North Carolina, interviews of serologically confirmed LACE patients or the parent(s)/guardian(s) of the case patients were conducted. The estimated burden of LACE was divided into three categories: direct medical costs; indirect medical costs; and social costs. Direct medical cost is the dollar value associated with medical treatment and rehabilitation for LACE. Indirect medical costs refer to any lost income and/or expense required that is not involved in treatment or rehabilitation of a person with LACE. Social costs were measured with Disability Adjusted Life Years (DALYs) and the Impact of La Crosse Encephalitis Scale (ILCES). DALYs are a non-monetary estimate of productive life years lost due to an illness or health event, while ILCES scores measure the affect of LACE on the overall emotional and social well being of the case patient and family. Participants exhibited three severities of LACE: frank encephalitis with no sequelae (n = 4); frank encephalitis with limited sequelae (n = 16); and frank encephalitis with lifetime sequelae (n = 5). The total cumulative time of study, date of onset of LACE to date of interview, for all case patients within the three disease severity classes was 100.59 life years. The total direct and indirect medical costs associated with LACE for 100.59 life years of the 25 patients with frank encephalitis was $794,303, ranging from $7,521 - 175,586 for individual case patients. On average, the direct and indirect medical costs of a single case of LACE were $32,974 (± SD = 34,793, n = 25). The projected cost of a case of LACE with lifetime neurological sequelae ranged from $48,775 to $3,224,831 (n = 5), depending on severity of sequelae. Quantitative and qualitative measures of the socioeconomic burden of LACE are included in the analyses to create an estimate addressing both the economic and social impacts of LACE on the family. For the 25 LACE patients, 55.19 of 100.59 life years (54.83%) were impaired to some degree. Along with impaired life years, approximately 13.00 DALYs were accumulated for the 25 patients over 100.59 life years of study. ILCES scores demonstrate the majority of the social burden is borne by patients with lifetime, neurological sequelae (n = 5). Projected DALY estimates for individual patients with lifetime neurological sequelae ranged from 12.90 ? 72.37 DALYs, depending on DALY type and estimated life expectancy used. The socioeconomic burden resulting from LACE is substantial, which highlights the importance of the illness in western North Carolina, as well as the need for active surveillance and prevention programs for the vector/virus complex.
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    Effects of Synthetic Chemicals and Bacteria on the Oviposition Behavior and Electroantennogram Responses of Aedes albopictus (Diptera: Culicidae)
    (2002-07-16) Trexler, Jonathan David; D. Wes Watson, Committee Member; Coby Schal, Committee Member; Charles S. Apperson, Committee Chair; W. Scott Chilton, Committee Member
    Five volatile synthetic chemicals (dimethyl disulfide, indole, 4-methylphenol, 3-methylindole, and trimethylamine) were tested as potential oviposition attractants of Aedes albopictus (Skuse) in laboratory and field experiments. In addition, the oviposition responses of Ae. albopictus to bacterially-enriched substrates were evaluated in behavioral and electrophysiological bioassays as sources of attractants and stimulants. None of the five synthetic chemicals elicited a significant positive oviposition response. In laboratory bioassays that measured attraction of gravid females to olfactory stimuli, compounds were evaluated over a range of concentrations that spanned 4-5 logs. Three concentrations of 4-methylphenol and one concentration of 3-methylindole were significantly repellent. All other concentrations of the five chemicals tested did not attract more females than a water control. The five synthetic compounds were loaded into controlled-release packets, which were used to bait water-filled ovitraps at five suburban residences. Aedes albopictus exhibited no oviposition preference for any of the baited traps versus adjacent traps containing only water. In addition, there was no difference in the mean number of eggs laid per trap-day by Ae. albopictus among ovitraps treated with each of the five compounds. Electoantennography indicated that Ae. albopictus did not exhibit a physiological response to any of the five chemicals at 0.025 mg/L. The oviposition responses of Ae. albopictus to bacterially-enriched substrates were evaluated in laboratory bioassays. Gravid mosquitoes responded to volatiles from larval rearing water (LRW) and soil-contaminated cotton towels (T). Bacterial species were isolated from these substrates and from an organic infusion made with oak leaves (OLI). Through fatty acid-methyl ester analyses, 6 bacterial isolates from LRW, two isolates from T, and three isolates from OLI were identified to species. The response of gravid mosquitoes to these isolates was also evaluated in behavioral bioassays. Water containing Psychrobacter immobilis (from LRW), Sphingobacterium multivorum (from T) and an undetermined Bacillus species (from OLI) elicited significantly higher oviposition than control water without bacteria. Only volatiles collected from LRW elicited significant electroantennogram responses in females.