Masters Theses

Date of Award

12-2002

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Reid R. Gerhardt

Committee Members

Jerome Grant, Carl Jones

Abstract

Peridomestic landscape factors were investigated in 2000 and 2001 at 24 La Crosse (LAC) encephalitis and 79 control sites in an eleven county region in eastern Tennessee to determine the factors that place residents in these counties at risk for LAC encephalitis. Data collected included the condition of the home and yard, distances from the home to the road and tree line, presence and number of artificial containers and tree holes, and the habitat type of the surrounding area. Oviposition traps and CO2-baited Centers for Disease Control (CDC) miniature traps (lights removed) were deployed at each residence. Adult mosquitoes reared from the collected egg strips from the oviposition traps were identified to species, sexed, counted and placed into lots of <-50 individuals, and frozen at -80 °C. The lots were sent to the CDC Division of Vector-Borne Infectious Diseases (DVBID) in Fort Collins, Colorado, for virus isolation. Results were compared between LAC encephalitis and control sites to identify any possible differences that were present.

LAC encephalitis sites commonly had more disposable containers, and had one or more tree holes present on the premises in comparison to control sites. LAC encephalitis sites were commonly in mature and successional forests; whereas, most control sites were in the suburbs. Most of the LAC encephalitis cases were in close proximity to the forest (less than 15.2 m), and most control cases were farther than 30.4 m away from the forest. "Moderately maintained" homes were more commonly encountered at LAC encephalitis sites than at control sites. Aedes albopictus female larvae and pupae were more likely to be encountered at the LAC encephalitis sites than at the control sites in tree holes or artificial containers. The overall mosquito burden (larvae/pupae collected and host-seeking adults from adult traps) for Ae. albopictus was statistically higher at the LAC encephalitis sites than at the control sites.

Mean elevations, mean permanent containers, all yard conditions, and mean tree holes at LAC encephalitis or control sites were not significantly different, and no arboviruses were isolated from mosquitoes collected or reared from any of the sites.

A survey evaluating receptacle type, type of substrate, amount of water, color of water, and amount of organic material in receptacles was recorded at 65 sites (56 controls and 9 LAC encephalitis sites) in 2001. Bird baths, plastic tarps, paint jugs (3.8-Liter), bowls, pans, and lids were common at control sites. More tree holes and permanent containers were found on control premises. Sunlit and partially shaded containers were more plentiful at control sites. Containers with no water, and ¼, ½, and completely full of water were predominantly observed at control sites. Containers at control sites contained clear water, had less organic matter, and had a higher percentage of mosquitoes present.

Tires were common around LAC encephalitis sites. Greater percentages of disposable containers were located on LAC encephalitis premises. Totally shaded containers were encountered mainly at LAC encephalitis sites. Most of the containers found on LAC encephalitis premises were 3/4 full. Containers from LAC encephalitis sites were mostly light yellow in color. LAC encephalitis sites had higher percentages of no mosquitoes present. Containers with various substrates (leaves, grass, soil, etc.) were predominantly encountered at LAC encephalitis sites.

Mixed substrates were the most predominant substrate type contained in all containers holding Ae. albopictus larvae that developed to adults in the laboratory. Permanent containers and tree holes holding Ae. albopictus larvae were most frequently encountered in completely shaded conditions. Disposable containers with Ae. albopictus larvae present in them were found in both sunlit and completely shaded conditions. Completely shaded permanent containers were the most commonly found combination containing Ae. albopictus larvae.

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