Predicting Local Transmission of Zika in the United States

A study has determined that while weather conditions may be suitable for the mosquitoes that carry the Zika virus throughout the the United States, typically we see the Aedes (Ae.) aegypti mosquito during summer months (July-September). The highest concentration of these mosquitoes will occur in the Southeast and South Texas.

The researchers who published their work in PLOS Current Outbreaks, analyzed 50 US cities in or near the range where the specific type of mosquito, Ae. aegypti, carries and transmits the Zika virus is known to appear. They note that socioeconomic factors will likely influence contact with mosquitoes that carry the virus with impoverished communities at a higher risk due to elevated risk factors, such as lower use of air conditioning, poorer housing infrastructure, and decreased access to safe water and sanitation.

While the abundance of the mosquitoes was zero or near zero in the United States in January, with the exception of Southern Florida and Texas, the authors expect that to change as the weather warms. For example, by mid-summer, cities like Denver, Albuquerque and Louisville, which are not always in the range for Ae. aegypti, will see a potential abundance of the infected mosquitos.

However, the summer months are not the only times of risk. Conditions for the Ae. aegypti will remain suitable through November for southern and western states. Then, by December, most of the country will be unsuitable again with the exceptions of Southern Florida and Texas.

Furthermore, introduction of the virus into local populations of Ae. aegypti is more likely seen in cities that have high volumes of people arriving from areas where there is already transmission of the Zika virus going on, such as Houston, Texas; Miami, Florida and Orlando, Florida, as well as towns along the US-Mexico border.

However, one limitation of the study is that it only included the contiguous United States, so states and territories where risk of transmission of Ae. aegypti-transmitted viruses is already high, such as Hawaii, Puerto Rico and areas in the South Pacific were excluded.

“Despite the limitations, our analysis is a step towards simultaneously mapping the geographic and seasonal suitability of the vector mosquito Ae. aegypti in the contiguous United States,” the authors concluded. “There is a need for enhanced, long-term, nationally-coordinated, local-level surveillance of both Aedes mosquitoes and Aedes-transmitted viruses, particularly in areas where simulations indicate Ae. aegypti populations may be high and coincide with more frequent travel between the U.S. and countries where Zika is circulating.”