Zika spread depends on amount of time people spend outdoors

By:  Tessa Gregory

Zika spread depends on amount of time people spend outdoors

Zika virus — carried by Aedes aegypti mosquitos in select tropical and subtropical regions of the world — is often transmitted indoors in developing countries. But in the United States, the majority of mosquito bites occur outdoors. Therefore, local patterns of how much time people spend outside are likely to contribute to how mosquito-borne viruses, including Zika, are spread.

In a study recently published in PLOS Neglected Tropical Diseases, Marco Ajelli of Northeastern University in Boston, along with colleagues at the University of Miami, surveyed 270 residents of Miami-Dade County, Florida, about their time spent outdoors and analyzed previously published national data on people’s outdoor time. Then, they incorporated the results into a computational model to determine how Zika transmission dynamics related to time spent outdoors.

The researchers found that the amount of time spent outdoors by people in Miami-Dade County was highly variable; most people spent little time outdoors (less than two hours a day) but a small percentage of people spent a large amount of time outdoors. Their modeling then revealed that this heterogeneity — compared to a hypothetical population in which everyone spent the same average amount of time outside — leads Zika virus to infect fewer people but spread at a faster pace from person to person.

“This highlights the need to derive new indices to be considered by operational mosquito control programs, categorizing neighborhoods on the basis of both mosquito surveillance counts and human outdoor exposure risk,” the researchers say. “Operation control efforts could be prioritized and directed toward areas characterized by high levels of human outdoor activities, such as recreational areas and tourist attractions, rather than, for instance, on residential areas.”

Reference: Ajelli M, Moise IK, Hutchings TCSG, Brown SC, Kumar N, Johnson NF, et al. (2017) Host outdoor exposure variability affects the transmission and spread of Zika virus: Insights for epidemic control. PLoS Negl Trop Dis 11(9): e0005851. https://doi.org/10.1371/journal.pntd.0005851

Image Credit: Stephen Ausmus (USDA), Flickr

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