Updated CDC map shows 21% increase in US counties reporting mosquito that transmits Zika
Last year, with the Western Hemisphere in the grip of a surprising Zika virus epidemic, CDC researchers used a survey to compile a list of U.S. counties where the mosquito at the heart of the epidemic, Aedes aegypti, had been documented over the past 21 years. They also documented counties that reported finding another mosquito, A. albopictus, known to transmit chikungunya and dengue viruses. The researchers said their data could be used to guide surveillance and mosquito control efforts across the country.
This week, the same researchers from the CDC’s Division of Vector-Borne Diseases released updated findings from the project that showed an increase in the number of counties reporting the mosquitoes, including a 21% increase in counties with A. aegypti.
Months after the first study was released last June, the U.S. experienced cases of locally transmitted Zika virus for the first time, first in Florida, then in Texas. The infections were acquired through the bite of infected A. aegypti mosquitoes, the primary way Zika is transmitted.
According to Micah B. Hahn, PhD, MPH, epidemiologist and disease ecologist in the Division of Vector-Borne Diseases, and colleagues, because intensified surveillance connected to the Zika epidemic was expected to produce new county-level mosquito collection records, they decided to repeat their survey at the end of 2016 to get an updated count.
“Additionally, respondents to the initial CDC survey have had more time to mine their historical mosquito surveillance records since the initial survey ended,” they wrote in a report published in the Journal of Medical Entomology.
The new report updates the number of counties that collected A. aegypti and A. albopictus mosquitoes between 1995 and 2016. Results were acquired through a county-level survey that Hahn and colleagues distributed to vector control professionals, entomologists and state and local health departments.
For the purposes of the study, counties that collected at least one Aedes mosquito at any life stage were recorded. To get a sense of areas with established populations of the mosquitoes, Hahn and colleagues noted how many years each species had been collected in each county.
According to the results, 38 more counties reported documenting A. aegypti mosquitoes between 1995 and 2016, an increase of 21% over last year’s total. Most of the counties are located in Texas, but the new results also included counties in Illinois and Alabama that previously lacked collection records, Hahn and colleagues reported. They said 40 counties, primarily in southern California, Kansas and Texas, reported additional years of collection data on top of what was included in last year’s report.
In total, 220 counties in 28 states and the District of Columbia reported finding at least one A. aegypti mosquito, including every state in the southern tier of the U.S., according to Hahn and colleagues. They said 101 counties from 16 states and the District of Columbia reported finding the mosquito in 3 or more years.
Many more counties —1,368 in 40 states and the District of Columbia, an increase of 10% — recorded the presence of A. albopictus. Of the 127 new counties reporting the presence of A. albopictus, most are in Arkansas, Kansas, Mississippi and Texas, Hahn and colleagues said. Approximately 573 counties in 34 states and the District of Columbia reported collecting the mosquito in 3 or more years.
According to Hahn and colleagues, 177 counties — mostly located in Arizona, southern California, Florida, Maryland and Texas — reported collecting both mosquitoes during the study period.
“These findings highlight the need for continued and improved mosquito surveillance,” the CDC said in a statement. “State and local health departments and mosquito control districts can use this information to plan for mosquito control and prevention activities in advance of possible outbreaks of mosquito-borne diseases.” – by Gerard Gallagher
Disclosure: The researchers report no relevant financial disclosures.