Our laboratory uses quantitative methods to understand the epidemiology and ecology of mosquitoborne viruses. We rely on modeling as a framework to improve our understanding of transmission mechanisms and to guide field and laboratory research that explicitly acknowledges the complexities of both the natural processes and the surveillance “lens” through which they are observed to produce answers that are evidence-based and readily interpretable by policy-makers.
Our research is highly collaborative, and relies on a diverse range of extramural resources, from federal agencies to state and local public health and mosquito control agencies. Much of our research has focused on the West Nile virus (WNV) system, and our interests have expanded in recent years to include other vector-borne pathogens of global importance, such as dengue virus in Peru (NIH P01 collaboration with Tom Scott), bluetongue virus in California (USDA-funded collaboration with Jim MacLachlan), and recently, Zika virus (NASA-funded research and other collaborations with Co-PI Lark Coffey).

Invasive mosquitoes and viruses. Aedes aegypti and Aedes albopictus, the primary vectors of dengue, Zika, and chikungunya viruses, are spreading rapidly in California, with many new detections in southern California and the Central Valley over the past two years. Coinciding with the invasion of these mosquitoes, the western hemisphere also has experienced the first documented massive outbreaks of chikungunya and Zika viruses following introductions into our hemisphere in 2013 and 2014, respectively. Cases have occurred throughout the Americas south of the U.S. since, at levels that are on par with the scale of dengue transmission. Zika, chikungunya, and dengue now present a serious threat of importation into California due to the presence of the invasive mosquitoes and the regular return of travelers infected with the viruses.

In areas infested by invasive mosquitoes, mosquito control efforts have not achieved eradication, and a better understanding of the fine-scale processes that affect spread and control are needed. We have a three-year research project funded by NASA to develop models and decision-support tools for estimating climatic suitability for the mosquitoes and simulating mosquito spread, and to estimate the risk of Zika, chikungunya, and dengue viruses in the U.S. and southern Europe. The project is a collaboration with Fondazione Edmund Mach (Trento, Italy), NASA Ames Research Center, UC Riverside, University of Washington, California Department of Public Health (CDPH), Centers for Disease Control and Prevention (CDC), and member agencies of the Mosquito and Vector Control Association of California.

Environmental drivers of arboviral transmission over space and time. Transmission of mosquitoborne viruses, which results from interactions among hosts, vectors, and pathogens, is strongly affected by climate and other anthropogenic factors such as irrigation and land land use change. These processes are dynamic, and our research strives for a mechanistic understanding of the heterogeneous processes that drive transmission of mosquitoborne viruses. Specific research questions focus on the causes of outbreaks of arboviral diseases and the factors that allow them to persist between years.

As part of the Research and Policy in Infectious Disease Dynamics (RAPIDD) program funded by NIH’s Fogarty International Center, C Barker led a working group that developed and validated detailed models for the transmission of WNV and Rift Valley Fever virus (RVFV), with parameters estimated from California studies and validated using our statewide surveillance data. An extension of this work has resulted in a model to understand temperature’s effects on bluetongue virus in California.

Evaluation and improvement of arbovirus surveillance and control. Public-health priorities continue to shape our laboratory’s research and service, especially the interests of California stakeholders, including CDPH and local mosquito and vector control agencies throughout the state. Much of our work aims to answer timely, policy-relevant questions that inform public-health decisions, and we work closely with public-health partners to evaluate California’s surveillance program for arboviruses and to develop response guidelines and risk models.

We are California’s central surveillance laboratory for arboviruses, where we test mosquitoes and dead birds for arboviruses from local agencies throughout the state, and we maintain the CalSurv Gateway website, data systems, maps, and servers that facilitate reporting and exchange of California’s arbovirus surveillance data. The surveillance, data systems, and relationships with stakeholders are critical for our research, and our lab has been an integral part of California’s response to the emergence of Zika virus this year.

The spread and establishment of WNV across the U.S. since 1999 highlights the difficulty of containing zoonotic pathogens, and WNV continues to cause human disease in California every year. Mosquito control is the primary method for limiting transmission risk, but better analytic methods are needed for understanding the collective impact of pesticide applications and other control treatments at the population scale. Building on our surveillance and pesticide application databases and new statistical approaches, we are conducting research to quantify the impacts of current mosquito control practices and to inform future development of adaptive strategies that can reduce our reliance on pesticides and better target control.