Study suggests that the risk of Zika virus transmission is particularly high in the southeast as well as in south Texas, where locally-acquired cases of Aedes-transmitted viruses have been reported previously.
The risk for Zika virus transmission in regions of Latin America and the Caribbean has been firmly established; however, its status as a public health issue here in the United States—other than as a consideration for travelers to areas where incidence rates are high—remains open to debate.
Recently, a multidisciplinary team of researchers that includes climatologists, public health specialists, epidemiologists, entomologists, mathematicians, and even mental health professionals, attempted to establish what they describe as “a baseline risk for local Zika virus transmission in the US and [recommendations for] the optimal timing of vector control activities” nationally. Their findings were published online on March 16 by the journal PLOS Currents/Outbreaks.
Of course, the ongoing Zika virus pandemic in Latin America and the Caribbean has led many federal, state and local government agencies in the United States—including most recently, the New York City Department of Health—to establish protocols for reducing the likelihood that travel-related introduction of Zika virus could initiate local transmission. The Zika virus has been particularly problematic in Brazil, where its primary vector, the mosquito Aedes aegypti, is prevalent. The virus has been associated with multiple complications, including microcephaly in newborns born to pregnant women who contract the virus.
Rohit Bhalla, DO, Chief of the Section of Infectious Diseases at the University Medical Center of Princeton, explains why the Zika virus is “scarier than [the CDC] originally thought.”
For the PLOS paper, the research team developed meteorologic models for the period of 2006 to 2015 that were designed to simulate the potential seasonal abundance of adult Aedes aegypti for 50 cities (including Atlanta, Houston, Miami and Washington, DC, as well as other large metropolitan areas) within or near the margins of its known US range (primarily the southeastern part of the country as well as the shared border with Mexico). They analyzed mosquito abundance results as well as travel and socioeconomic factors (for example, impoverished communities are typically at higher risk for infectious disease outbreaks) that have been linked with viral introduction and vulnerability to human-to-vector contact in other insect-borne diseases.
In general, their analysis concluded that meteorological conditions are “largely unsuitable” for Aedes aegypti in the United States during the winter (December to March), except in southern Florida and south Texas. In these generally warmer climates, they found that conditions can “sustain low-to-moderate potential mosquito abundance.” However, during the summer months (July to September), meteorological conditions are suitable for the mosquito in all 50 cities included in the analysis, even though there has been no documented evidence that the species currently inhabits these areas. The models used in the study suggest the risk is particularly high in the southeast as well as in south Texas, where locally-acquired cases of Aedes-transmitted viruses have been reported previously.
The authors of the PLOS paper did not respond to requests for comment at press time. However, in their concluding remarks, they write that, “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 US-Mexico border may correlate with factors that increase human exposure to Aedes aegypti. Our analysis is a step towards simultaneously mapping the geographic and seasonal suitability of the vector mosquito Aedes aegypti in the contiguous United States. 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 Aedes aegypti populations may be high and coincide with more frequent travel between the US and countries where Zika is circulating.”
Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous healthcare-related publications. He is the former editor of Infectious Disease Special Edition.