Research Projects

We are currently pursuing three primary areas of research:

Dengue emergence in the Arizona-Sonora Desert Region (NIH R01 Abstract)

Aedes aegypti mosquitoes are the primary vector for dengue, yellow fever and chikungunya.  The vector is present in most urban communities stretching along the U.S.-Mexico border yet dengue transmission has only been noted in two U.S. border communities in Texas, notably Brownsville and Laredo, TX.  While many argue that this is a result of different social factors across the border, this fails to explain the lack of transmission in some communities in northern Mexico, notably Nogales, Sonora.  Nogales is a large urban area on the Mexican side of the border with large vector populations and a constant influx of people from dengue endemic areas yet no local cases have been recorded.  Vector presence alone is not sufficient to cause disease transmission; vectors must also survive long enough to blood feed and become infected, have the parasite develop and feed again, transmitting the virus. 

Climatic influences on the lifespan and behavior of Ae. aegypti may also influence the risk of dengue transmission in this region which lies at the boundary of both virus and vector. Geographic areas such as this, at the edge of the range of disease and vector, are at greatest risk of emergence and reemergence of infectious diseases. We will assess the relative age structure of Ae. aegypti populations in nine cities with varying climates in the southern United States and Sonora, MX by trapping and molecularly determining the ages of adult Ae. aegypti during four mosquito seasons. We expect that cities with extremely dry and hot conditions will have younger Ae. aegypti populations. Cities with reported dengue transmission we expect to have Ae. aegypti that are on average younger when taking their first blood meal than cities without transmission.

To determine how the age of Ae. aegypti population vary over a finer spatial scale, we will sample adults in 150 households in Hermosillo, Mexico; a city with a history of dengue outbreaks. Additionally, we will survey the households for potential social and environmental factors that mediate the relationship between climate and longevity.  We expect to find significant variability across households.  Residences with older mosquitoes will have more vegetation, fewer barriers to mosquito access and indoor resting sites, no competing vector species and no control measures.

From the information gathered in the first two objectives, we will construct a model to predict the likelihood of the expansion of Ae. Aegypti populations that survive long enough to transmit dengue and thus changes in risk of dengue transmission. We expect that models of risk of dengue under climate change scenarios will decrease in areas that surpass a heat and dryness threshold and will increase in populations with increasing moisture. 

Increasing ownership and use of insecticide-treated bednets in western Kenya (NIH R15 Abstract):

Despite dramatic improvements, malaria remains a significant health problem in many regions of the
world. As malaria programs move from control to elimination, there is an urgent need to understand barriers to and facilitators of the use of control measures. In this proposal, we focus on the most widely used control measure; bednets in a highland/low transmission and a lowland/high transmission. Our preliminary results indicate that in Kenya roughly 1 in 4 children under 5, the group most vulnerable to malaria, live in households that do not own a bednet. Additionally, even in net owning homes, 1 in 6 children under 5, do not sleep under a net. As Kenya and other programs expand their scope to distribute enough nets to cover all household members, much effort needs to go into understanding the prevalence of and factors related to disuse. The objective of the following proposal is to use qualitative and quantitative methods to determine the prevalence of ownership, misuse and disuse of bednets under field conditions and to identify modifiable risk factors. We will use an ecological approach to assess not only individual level factors that drive bednet ownership and use but the social and environmental context in which these decisions are being made.

Following focus group discussions with community members and key informant interviews with health clinic staff, government vector control staff and village and community leaders, we will conduct a cross-sectional survey that examines 1) perceived susceptibility to malaria 2) perceived severity of malaria 3) perceived benefits of ITN use 4) perceived barriers to ITN use 5) cues to action such as health promotion programs and 6) confidence in the subject’s self-efficacy with regard to obtaining an ITN and its proper use. We will use remotely-sensed images and GIS to determine how these perceptions and practices vary geographically and if they correspond with actual risk as determined through parallel parasite prevalence surveys and pyrethrum spray catches of Anopheles. From the cross-sectional participants we will identify positive deviants, community members who own and use bednets regularly despite experiencing at least 75% of the factors associated with not owning or using a bednet. In-depth interviews will be conducted to determine their solutions and personal motivators that may be used to improve community bednet ownership and compliance.

Our approach is unique in its combination of rich qualitative data and the rigor and generalizability of
established epidemiologic methods. Identifying what is already working in a community is more likely to be
successfully implemented as a larger intervention. We expect that we will find that individuals who have
personal loss due to malaria, have identified solutions to logistical issues with hanging bednets, have a higher perception of risk and who have greater access to household resources will be more likely to own and use a bednet. This research will help drive the development of targeted community-based interventions that should improve ITN ownership and use and ultimately reduce malaria transmission.

Identifying factors associated with vaccine hesitancy in Arizona

Vaccine exemptions are currently an area of intense focus in public health. Universal recommendations for vaccination in the United States have substantially reduced the morbidity and mortality from several diseases (1).  The Institute of Medicine (IOM) recently completed an exhaustive report on the safety of eight recommended vaccines, and concluded that while there can be rare adverse events after vaccination, the benefits of the program far outweigh the risk (2). In the United States, all states and the District of Columbia have laws requiring vaccinations for entry into public schools; however, approximately 20 states allow for parents to waive vaccines based on personal beliefs. The protocol for obtaining these personal belief exemptions (PBEs) varies widely by state (3, 4), and Arizona is one of approximately 10 states with the easiest procedures for obtaining exemptions (5). This is of concern because the ease of obtaining exemptions has been directly associated with increased incidence of pertussis (4, 6) and measles (7). Of note, the rate of vaccine exemptions has tripled in Arizona in the past decade(5), and concurrent with this rise, Tucson experienced a measles outbreak in 2008 that cost over $800,000 to contain (8).

When parents request an exemption from immunizations that would otherwise protect their children from vaccine preventable diseases (VPDs), the repercussions extend to and place a significant risk upon not only on their children but also on the health of other individuals in their communities, particularly in areas where there are geographic clusters of vaccination exemptors (6). Our preliminary data demonstrate that such clusters exist in Arizona, though the reasons for this are unclear. The individuals involved or affected include not only the children of parents who have exempted them based on their own personal beliefs but also include immune-compromised children who were exempted due to medical purposes, as well as children who are too young to be vaccinated (9). Interestingly, children and adults who are immunized are also at risk because vaccines are not 100% efficacious and, while parents may believe that they are exercising their individual freedom and autonomy, by exempting their children from vaccination, they are doing so at the cost of public health by causing an increase in the risk for outbreaks of VPDs (10). Additionally, PBEs are not randomly distributed across Arizona. High clusters of exemptions have been detected in Yavapai and Maricopa Counties. People residing in these communities have a higher risk of outbreaks of VPDs.