East Coast, South at Greatest Risk for Zika in Continental US

Tara Haelle

March 18, 2016

A number of major cities throughout the South and along the East Coast will have weather conditions ripe for the Aedes aegypti mosquito, the vector for Zika virus, during the summer months, according to a study published online March 16 in PLOS Currents. Although southeastern Florida and the southernmost tip of Texas are most likely to have higher abundances year-round, the entire Eastern corridor, eastern Midwest, and South have the potential to host the vector if the virus is introduced through international travel.

"Even if Zika virus arrives in the United States, transmission can be mitigated and reduced through the use of vector control strategies," write Andrew J. Monaghan, PhD, from the National Center for Atmospheric Research, Research Applications Laboratory in Boulder, Colorado, and colleagues. "It is clear, however, that vector control and public health interventions should consider tailoring their messages to the local communities."

The researchers used two distinct meteorological models from 2006 through 2015 to simulate the likely seasonal populations of adult A aegypti mosquitos for 50 US cities. Although not all the selected cities have reported the presence of A aegypti, all are within or near the mosquito's known geographical range and have suitable meteorological conditions for the species. The two models, DyMSiM and Skeeter Buster, estimate the daily counts of adult A aegypti mosquitos per 1 square meter of water surface, including standing open water such as kiddie pools, bird baths, and puddles after lawn watering.

Weather conditions from December through March are typically unfavorable for A aegypti mosquitos in all regions except southern Florida and south Texas. From July through September, however, the weather conditions are ideal for the mosquitos in all the cities examined. The researchers categorized mosquito abundance relative to the mosquito's mean abundance in Miami from May to October. "None to low" referred to abundances below 2% of the Miami May–October mean and was unlikely to result in human–vector contact. "Low to moderate" referred to an abundance from 2% to 25% of the Miami mean, "moderate to high" included 25% to 75% of the Miami mean, and "high" included anything above 75% of the Miami mean.

"We chose Miami and the May-October period because it is the warmest and wettest time of year in south Florida, a time when Ae. aegypti is known to be abundant and when most transmission of Ae. aegypti-borne viruses has occurred in the past," the authors write. "May-October in Miami thus represents high environmental suitability for Ae. aegypti."

The researchers then estimated the likelihood of Zika introduction into any of the cities, based on air and land border travel between the United States and countries and territories where the virus is currently circulating. They also considered the influence of socioeconomic factors on human–vector contact.

"Poverty has been linked to a number of indicators of elevated exposure to mosquitoes such as lower usage rates of air conditioning and less efficient cooling options, poorer housing infrastructure such as screening of windows, as well as decreased access to safe water and sanitation," the researchers write. Other factors include garbage collection frequency, water storage needs, and presence of discarded tires, for example.

By mid-July, abundance of A aegypti adults will likely be high in the Southeastern-most cities, including Miami, Tampa, Orlando, and Tallahassee in Florida; Jacksonville, Mississippi; Mobile, Alabama; New Orleans, Louisiana; Savannah, Georgia; and Charleston, South Carolina.

Among the cities suitable for moderate to high abundance by July who fall within the species' known range are Brownsville and Houston in Texas and, along the East Coast and in the Deep South, New York City; Philadelphia, Pennsylvania; Washington, DC; Richmond, Virginia; Raleigh and Charlotte, North Carolina; Columbia, South Carolina; Augusta and Atlanta, Georgia; Montgomery and Birmingham, Alabama; Jackson, Mississippi; and Shreveport, Louisiana.

Although suitable in the summer for the mosquito, Denver, Colorado; Albuquerque, New Mexico; Las Vegas, Nevada; Salt Lake City, Utah; Louisville, Kentucky; and several cities in northern California, the eastern Midwest, and Appalachia are not yet in the known range for A aegypti. However, nearly all the cities have the potential to support a low to moderate abundance of A aegypti from June through September, however.

A aegypti tends to prefer urban areas, whereas Aedes albopictus, another potential Zika vector, roams the rural South, where the poorest communities are found. Laredo and Brownsville in Texas were among the poorest urban areas, with poverty rates above 30% in their counties. Yuma, Arizona, and Miami similarly have rates above 20%, and poverty rates exceed 15% in several counties encompassing multiple Southern cities.

On the basis of international travel trends, "[h]igher risk is thus implied for U.S.-Mexico border cities and neighboring areas, where population movement is high, and larger air traffic hubs such as Houston, Los Angeles or Miami," the researchers write.

New Test Available for Zika

The Centers for Disease Control and Prevention (CDC) announced today that the US Food and Drug Administration has issued an Emergency Use Authorization for the Trioplex Real-time RT-PCR Assay. The assay simultaneously tests for chikungunya, dengue, and Zika infection, instead of requiring three separate tests.

The CDC will distribute the test to qualified laboratories in its Laboratory Response Network, which is an integrated group of laboratories prepared to address public health emergencies. The new test will not be available to other healthcare providers or laboratories.

In addition, the CDC also reported in a brief Morbidity and Mortality Weekly Report synopsis sent to the media today that 116 US residents were diagnosed with laboratory-confirmed Zika virus between January 1, 2015, and February 26, 2016. Of those, 110 cases occurred in people who had traveled to a region in which Zika is circulating, five occurred through sexual transmissions, and one was a congenital case.

The most common symptoms were rash (97%; N = 113), fever (82%; N = 94), and arthralgia (66%; N = 76).

The research was funded by the National Institutes of Health, the National Aeronautics and Space Administration, and the National Science Foundation. The authors have disclosed no relevant financial relationships.

PLOS Curr. Published online March 16, 2016. Full text


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