On the Seasonal Occurrence and Abundance of the Zika Virus Vector Mosquito Aedes Aegypti in the Contiguous United States

Abstract

Introduction: 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. 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. Meteorological conditions are suitable for Aedes aegypti across all fifty cities during peak summer months (July-September), though the mosquito has not been documented in all cities. Simulations indicate the highest mosquito abundance occurs in the Southeast and south Texas where locally acquired cases of Aedes-transmitted viruses have been reported previously. Cities in southern Florida and south Texas are at the nexus of high seasonal suitability for Aedes aegypti and strong potential for travel-related virus introduction. Higher poverty rates in cities along the U.S.-Mexico border may correlate with factors that increase human exposure to Aedes aegypti.

Discussion: Our results can inform baseline risk for local Zika virus transmission in the U.S. and the optimal timing of vector control activities, and underscore the need for enhanced surveillance for Aedes mosquitoes and Aedes-transmitted viruses.

Fig. 1. U.S. map showing 1) Ae. aegypti potential abundance for Jan/July (colored circles), 2) approximate maximum known range of Ae. aegypti (shaded regions) and Ae. albopictus (gray dashed lines), and 3) monthly average number arrivals to the U.S. by air and land from countries on the CDC Zika travel advisory. Additional details can be found in the text.

Table 1. Coordinates, population and climate characteristics ^, for the 50 study cities.

Fig. 2.The 2006-2015 ensemble mean monthly average Ae. aegypti potential abundance.

Fig. 3. 2006-2015 average simulated monthly Ae. aegypti potential abundance versus average observed abundance for Miami (2006-2008; top) and Phoenix (2006-2015; bottom). Results are expressed as a fraction of the maximum monthly abundance for each dataset in order to facilitate comparison (otherwise abundance measures will vary widely due to how simulated versus observed mosquitoes are quantified and the areal extents they represent).

Fig. 4. 2014 monthly number of persons arriving by air from Latin American countries on the CDC Zika travel advisory (top), and by land from Mexico (bottom). Sources for data can be found in the text.

Fig. 5. 2014 percentage of households below the poverty line by U.S. county. Source of data can be found in text.

Fig. S1. Locations of know occurrences of Ae. aegypti and Ae. albpictus in the U.S. for 1960-2014 reproduced from Kraemer et al. ^{, ,} and updated with collections in California for 2011-2015 .

Fig. S2. The 2006-2015 Skeeter Buster mean monthly average Ae. aegypti potential abundance.

Fig. S3. The 2006-2015 DyMSiM mean monthly average Ae. aegypti potential abundance.