Aedes aegypti mosquitoes are the primary vectors for Zika, dengue, chikungunya, and yellow fever viruses, all of which have the potential to cause severe and life-altering clinical manifestations. To date, a widely accepted vaccine exists only for yellow fever virus, and the primary means of preventing Zika, dengue, and chikungunya transmission is through reducing human-Ae. aegypti contact with vector control and personal protective measures. In the past decade, widespread outbreaks of Zika (ZIKV), dengue (DENV) and chikungunya (CHIKV) viruses have occurred in the Americas, including the United States. Since 2013, Ae. aegypti populations have been growing and spreading in California. Local transmission of Ae. aegypti-borne viruses has not been detected in the state, although California consistently has some of the highest rates of travel-associated infections of ZIKV, DENV, and CHIKV annually. In the tropics, where Ae. aegypti and DENV are endemic, poverty and deteriorating housing conditions have been associated with increased DENV transmission. In California, where housing conditions and human behaviors differ from those of the tropics, it is unclear how socioeconomic status, housing characteristics, and human behaviors may modify the risk of local Ae. aegypti-borne virus transmission. This study defines the transmission potential of Ae. aegypti-borne viruses in Los Angeles County, California by assessing variation in Ae. aegypti abundance, biting patterns, and transmission dynamics relative to socioeconomic status, household characteristics, and human behaviors.
Initially, we conducted a cross-sectional study in Los Angeles County, California during summer 2017 to understand the causes of variation in relative abundance of Ae. aegypti among households. We surveyed and collected mosquitoes at 161 houses, representing a wide range of incomes. Aedes aegypti abundance outdoors was higher in lower-income neighborhoods and around older households with larger outdoor areas, greater densities of containers with standing water, less frequent yard maintenance, and greater air-conditioner use. Aedes aegypti abundance indoors was higher in households that had less window and door screening, less air-conditioner usage, more potted plants indoors, more rain-exposed containers around the home, and lower neighborhood human population densities. Our results indicate that there are behavioral and socio-demographic determinants of Ae. aegypti abundance in southern California.
Secondly, to understand how Ae. aegypti feeding patterns may influence transmission in the U.S., we developed a novel method to identify the feeding histories of field-caught Ae. aegypti using the anthrone and vanillin assays. We then identified the blood meal hosts and the blood and sugar feeding prevalence of Ae. aegypti collected in Los Angeles County. Of the 39 blood-engorged Ae. aegypti we tested, we found that 85% of blood-fed Ae. aegypti had fed on human hosts, and the remaining 15% had fed on dogs. Additionally, 29% of non-blood-engorged females were positive for fructose, 63% had evidence of having only fed on sugar, and 37% had evidence of having taken blood and sugar. This study enhances our understanding of Aedes-borne virus epidemiology in relation to Ae. aegypti feeding patterns in the U.S., which is important for targeting vector control in the arid southwest where travel-related infections are common and Ae. aegypti and other vectors continue to spread.
Finally, we combine the findings from the previous two chapters to characterize the dengue transmission potential in Los Angeles County. In this chapter, we estimated the basic reproductive number of dengue virus as a function of the relationships between household characteristics, human behaviors, and Ae. aegypti abundance and biting that were characterized in the previous Chapters 1 and 2. We found that the dengue virus reproductive number is consistently higher in low-income areas mostly due to variables that are associated with increases in Ae. aegypti blood feeding. Understanding these dynamics in Los Angeles County will provide a better understanding of the Ae. aegypti-borne transmission potential in other urban U.S. cities.
The results of this dissertation indicate that there are heterogeneities in dengue virus and other Ae. aegypti-borne virus transmission potential across neighborhoods and socio-demographic groups in Los Angeles County, and that low-income groups are at greater risk of dengue virus transmission than high income groups. These studies identify specific risk factors for increases in Ae. aegypti abundance and human exposure to Ae. aegypti biting that will be useful for vector control and public health agencies developing mitigation and control strategies. Ultimately, this study provides compelling evidence that community-specific strategies that take into account neighborhood context and human behaviors should be developed to minimize Ae. aegypti-borne virus transmission risk in California and other urban regions of the United States.
|Advisor:||Barker, Christopher M.|
|Commitee:||Scott, Thomas W., Rocke, David M.|
|School:||University of California, Davis|
|School Location:||United States -- California|
|Source:||DAI-B 82/2(E), Dissertation Abstracts International|
|Subjects:||Epidemiology, Virology, Kinesiology|
|Keywords:||Aedes aegypti, California, Dengue, Socioeconomic status, Vector control, Zika|
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