Andrew J. Monaghan; Cory W. Morin; Daniel F. Steinhoff; Olga Wilhelmi; Mary Hayden; Dale A. Quattrochi; Michael Reiskind; Alun L. Lloyd; Kirk Smith; Chris A. Schmidt; Paige E. Scalf; Kacey Ernst

“ Multiple factors determine when and where arboviruses emerge; vector presence is only one factor that needs to be evaluated to assess the potential for disease emergence. Socioeconomic conditions that modulate human exposure to vectors play a role in population vulnerability to arboviruses [24] . Poverty is associated with lower air-conditioning use and less efficient cooling options [54] ; such conditions can lead to open windows and doors and raise the probability of human-vector contact. ”

“ An ongoing Zika virus pandemic in Latin America and the Caribbean has raised concerns that travel-related introduction of Zika virus could initiate local transmission in the United States (U.S.) by its primary vector, the mosquito Aedes aegypti.Methods: We employed meteorologically driven models for 2006-2015 to simulate the potential seasonal abundance of adult Aedes aegypti for fifty cities within or near the margins of its known U.S. range. ”

“ Human-filled containers can represent an important source of water for Ae. aegypti habitat in arid and semi-arid regions [37] . For both models, releasing new cohorts of eggs each month prevented extinction of mosquitoes, or (in the case of DyMSiM) when the population of any life stage reduced to zero. Releases ranged from 80-100 eggs per container. This choice essentially assumes that Aedes eggs are frequently reintroduced into areas through transportation networks [38] or that eggs are able to survive through periods when weather is unfavorable for development. ”

“ Mosquito abundance results were analyzed alongside travel and socioeconomic factors that are proxies of viral introduction and vulnerability to human-vector contact. Results: Meteorological conditions are largely unsuitable for Aedes aegypti over the U.S. during winter months (December-March) , except in southern Florida and south Texas where comparatively warm conditions can sustain low-to-moderate potential mosquito abundance. ”

“ However, in Miami the observed onset and cessation of peak summer abundance in June-July occurs more rapidly than in the simulations, which have a broader peak that extends later into the summer. Interestingly, our climate data indicate that daily maximum and minimum temperatures and rainfall in August-September are similar to June-July conditions, suggesting that very high abundance might otherwise be expected to extend into these later summer months. The difference between peak and off-season abundance in Miami is also more pronounced in the observations. ”

“ These cut points were chosen to provide a proxy of the lower quartile, the interquartile range, and the upper quartile with respect to Miami values. The “None to low” cut-point of 2% rules out extremely low abundance values that are unlikely to be sufficient to generate substantial risk for human contact.
Results of simulations of adult Ae. aegypti populations are referred to in terms of potential abundance in order to emphasize that they indicate meteorological suitability for the mosquito but not necessarily that it is present or will occur in a given location. ”

“ It is noteworthy that DENV transmission occurred in the contiguous U.S. prior to 2010, however those reported cases were more difficult to confirm and additionally were mainly from counties in Florida and Texas already identified as having DENV transmission using the (more reliable) data from 2010 onward.
Human exposure data Vector-human contact is likely modulated by socioeconomic factors. Impoverished communities are at higher risk of introduction of infectious diseases [53] . ”

“ Although Ae. albopictus is thought to be a competent vector of ZIKAV [14] , Ae. aegypti has been implicated as the primary transmitter of the virus in human populations in the ongoing outbreak in the Americas [15] . ”

“ The influence of humidity in the simulations may not be adequately represented, which could be an important issue in arid regions where desiccation may substantially impact adult survival [64] . Little is known of the geographic distribution of container characteristics such as type, quantity and degree of shading, all factors that regulate water temperature and amount available for immature development. Additionally, the degree and frequency of manual filling of potential container habitats by humans is virtually unknown and may be over- or understated in the models. ”

“ Despite these limitations, our validation indicates that overall the Skeeter Buster and DyMSiM simulations, as well as their ensemble mean, resolve the seasonal cycle of Ae. aegypti abundance in Phoenix and Miami. Importantly, the simulations capture the months of peak abundance in both cities. We also find that Skeeter Buster and DyMSiM have similar seasonal cycles of abundance at most U.S. cities (Figs. S2 and S3) .
Study limitations not related to the model simulations include incomplete information about travel from areas of ongoing Zika transmission. ”

“ While Ae. aegypti and Ae. albopictus are established across much of the southern United States (Fig. 1) , mosquito populations in many areas are only present seasonally. This seasonality varies according to local meteorological conditions, and thus can provide one measure of potential for ZIKAV transmission (i.e., local transmission may not be sustained if competent vector mosquitoes are not present) . ”

“ For example, because knowledge of egg survival during winter in marginal areas is limited [70] , we artificially introduce eggs into the simulations each month, which keeps eggs from becoming extinct in cities that have seasonal Ae. aegypti populations, but likely causes egg availability/viability to be overestimated. Cryptic habitats that are not represented in models may enhance environmental suitability during winter ”

“ Her primary research emphasis is on the human behavioral component of climate-sensitive health and disease issues, including community participatory research and the characterization of population vulnerability to weather and climate related health threats.Geographer and Senior Research Scientist pursuing research on the applications of NASA remote sensing data to public health and climate change.Kacey Ernst is an Associate Professor of Epidemiology and Biostatistics at the University of Arizona. ”

“ Disparities in income have been associated with intermittent or no access to piped water in unregulated communities (colonias) in the U.S.-Mexico border region [67] ; such conditions can necessitate water storage that in turn provides oviposition opportunities for Ae. aegypti. Intermittent garbage collection may also contribute to the provision of important oviposition sites along the U.S.-Mexico border. For example, discarded tires provide ideal habitat for Ae. ”

“ In this manner, the initial adult mosquito abundance results for both DyMSiM and Skeeter Buster were expressed for each 1 m2 of water surface area per city; these values were then normalized for presentation, as described below. Sheltering of containers (via shading) was also considered for both models because Ae. aegypti prefers shaded environments [40] . DyMSiM treated sheltering by reducing evaporation among 50% of containers and limiting the maximum water temperature to <34oC. Skeeter Buster assumed a sun exposure of 0.1 (i.e., 90% shade) for containers. ”

“ Skeeter Buster: a stochastic, spatially explicit modeling tool for studying Aedes aegypti population replacement and population suppression strategies. PLoS Negl Trop Dis, 3 (9) , e508. 1 2 Morin, C. W., Monaghan, A. J., Hayden, M. H., Barrera, R., & Ernst, K. (2015) . Meteorologically driven simulations of dengue epidemics in San Juan, PR. PLoS Negl Trop Dis, 9 (8) , e0004002. ↑ Semenov, M. A., & Stratonovitch, P. (2010) . Use of multi-model ensembles from global climate models for assessment of climate change impacts. ”

“ Local and regional spread of chikungunya fever in the Americas. Euro surveillance: bulletin Europeen sur les maladies transmissibles= European communicable disease bulletin, 19 (28) , 20854. ↑ Fischer, M., & Staples, J. E. (2014) . ”