Browsing by Author "Bradford, Carrie M."
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Item Effects of weather on mosquito biology, behavior, and potential for West Nile virus transmission on the Southern High Plains of Texas(Texas Tech University, 2005-08) Bradford, Carrie M.; Presley, Steven M.; Nisbett, Richard; McIntyre, Nancy E.; Cox, Stephen B.; Anderson, Todd A.The threat of emerging and resurgent vector-borne diseases associated with weather conditions, global climate change, and biologic attacks is of major concern. West Nile virus (WNV) first appeared in the United States in the summer of 1999. Since then it has spread rapidly across the nation and continues to be a threat to humans, domestic animals (particularly horses), and wildlife. The goal of this project was to model the factors involved in the WNV maintenance and transmission cycle. Mosquito surveillance to determine mosquito community dynamics and WNV infection in mosquito populations has been ongoing in Lubbock County, TX (33.65°N; 101.81°W; 975 m elevation), since the summer of 2002. West Nile virus was first detected in Lubbock County in late summer 2002 and has continued to appear each summer. The occurrence of WNV in mosquitoes collected over a three-year period was determined and related to very diverse annual weather conditions during those years in order to determine trends in WNV occurrence. Differences in weather conditions between study years was reflected in differences in mosquito collections and WNV maintenance and transmission. In the Lubbock area, 2003 was a drought year, and Culex tarsalis Coquillett dominated mosquito collections due to an abundance of stagnant pools that allowed for the proliferation of this species. Additionally, a large number of mosquito pools tested positive for WNV. The following year, however, was a wet year, and Aedes vexans Meigen, a floodwater species, dominated mosquito collections. During 2004, the number of WNV-positive mosquito pools was reduced by two-thirds, despite testing approximately the same number of pools. Modeling mosquito populations and WNV occurrence in relation to weather patterns revealed interesting trends. Both of these were predicted by weather conditions, typically rainfall and temperature, in the weeks prior to collection of WNV infected mosquitoes. By understanding the factors that drive mosquito populations and the occurrence of WNV, future patterns of disease occurrence can be predicted and efficient mosquito control operations can be initiated prior to a major disease outbreak. Models which explain when and why disease transmission occurred are important as related to effective surveillance and control activities as well as with respect to climate change and the potential for biologic attacks. Climate change is expected to increase the geographic distribution of many vector-borne diseases, and especially mosquito-borne diseases. Malaria, among other diseases, has already reappeared in regions in which it had previously been eradicated. Global warming that is projected to occur with climate change will allow for the geographic range of many mosquito species to be expanded, with the potential for these species to carry new diseases into naïve areas. Additionally, climate change is expected to increase the frequency of extreme events such as floods and droughts, which have previously been shown to facilitate the outbreak of various mosquito-borne diseases. Models of disease transmission will help public health officials initiate effective surveillance and proactive control strategies to prevent the further spread of disease. Acts of terrorism involving biologics is also of major concern. Models of disease transmission will aid in distinguishing between natural outbreaks of disease and a biologic attack. Understanding how a disease outbreak was initiated is also critical for effective surveillance and control operations, since biologic attacks could involve genetically altered pathogens, thus potentially requiring a different means of disease treatment or control.Item Perchlorate uptake and effects on thyroid function in fish(Texas Tech University, 2002-05) Bradford, Carrie M.Perchlorate salts occur in many forms including ammonium perchlorate and sodium perchlorate. Because perchlorate is used as an oxidizer in rocket propellants and explosives, contamination is common near military installations such as Longhorn Army Ammunition Plant. The toxicity of perchlorate involves the inhibition of iodine uptake by the thyroid follicular cells, thereby reducing thyroid hormone synthesis. This leads to an increase in the amount of TSH (thyrotropin-releasing hormone) and TRH (thyroid stimulating hormone) produced due to negative feedback. The continued stimulation of TSH on the thyroid follicular cells leads to hypertrophy, colloid depletion, and the formation of goiters. Thyroid hormones are important in metabolism, growth, development, and reproduction and have a permissive action on other tissues. Although the mechanism of action of perchlorate is known in humans, amphibians, and rats and there are studies that have been conducted in fish and amphibians, not much is known about the effects of environmentally relevant concentrations of perchlorate. Since perchlorate is water soluble, fish and other aquatic organisms receive the greatest exposure to perchlorate in contaminated areas. The purpose of this project was to determine the uptake of perchlorate into mosquitofish and various tissues in the catfish and the effects on thyroid morphology and function in mosquitofish. Mosquitofish were exposed to 0, 0.1, 1, 10, 100, and 1000 mg/L sodium perchlorate for 2, 10, and 30 d with 5 replicates per treatment group. Catfish were exposed to 100 mg/L sodium perchlorate for 5 d with 20 replicates. Tissue perchlorate concentrations in the catfish and mosquitofish were determined by extracting perchlorate from the tissues using accelerated solvent extraction with water, and then analyzing these extracts by ion chromatography. Histological slides of the mosquitofish thyroid follicles were analyzed for hypertrophy, hyperplasia, and colloid depletion. Whole body thyroxine (T4) concentrations in the mosquitofish were determined by radioimmimmunoassay (RIA). Perchlorate did not bioconcentrate in the fish; tissue concentrations in the mosquitofish were 10 times less than the exposure concentration. The highest concentration of perchlorate in the catfish was found in the head, but this was 4 times less than the exposure concentration. Perchlorate also induced hyperplasia, hypertrophy, and colloid depletion in mosquitofish exposed to the highest concentrations (10, 100, and 1000 mg/L) of perchlorate for the longest time periods (10 and 30 d). T4 concentrations in the mosquitofish were also significantly decreased in fish exposed to perchlorate as compared to the controls in fish exposed to 1000 mg/L for 30 d. At environmentally relevant concentration of perchlorate, there was little to no uptake of perchlorate into the whole body mosquitofish. Thyroid morphology and function were also only slightly modified by low doses of perchlorate. In contrast, exposure to high concentrations of perchlorate led to high concentrations of perchlorate in the various fish tissues, as well as disruptions in thyroid morphology and function. The results of this study are consistent with studies that have been conducted in humans, rats, amphibians, and other fish.