American Scientist

To the Editors:

I enjoyed Robert Dorit’s timely and thoughtful reflections in “Zika Goes Viral” (Perspective, September–October), which provide valuable context to this and other public health threats facilitated by globalization. I write to correct and expand upon information regarding the habits of the mosquito species involved in transmission of this virus.

When discussing the two invasive mosquito species in the United States that are capable of Zika transmission, Dorit says that the mosquito Aedes aegypti is “primarily diurnal, feeds outdoors, and ventures far from its birthplace,” while Aedes albopictus “feeds indoors, primarily in the mornings or evenings.” Contrary to this assertion about habitat preferences, A. aegypti is typically more urban and likely to bite indoors, whereas A. albopictus prefers more rural and vegetated habitats, especially in regions where the species co-occur. In the Americas, A. aegypti is more prone to feed from humans, but elsewhere in their extensive ranges A. albopictus may be the more anthropophilic species.

Where the distributions of the two species overlap, displacement of one species for the other has been documented, usually favoring A. albopictus. Although some commentators speculated that competitive displacements of A. aegypti by A. albopictus might be good for public health, replacing one disease vector species with another is not likely to be a reliable control strategy.

Although Dorit alludes to the detection of Zika in Africa in arboreal primate hosts, the column does not connect the natural forest life cycle of this virus between monkeys and arboreal mosquitoes with its invasion of the New World, where establishment of a sylvan life cycle in neotropical forests may lead to an endemic reservoir for reemergence of the disease. Indeed, the related yellow fever virus made this same transition centuries earlier to forests in Central and South America, which remain active sites of endemic yellow fever transmission to humans.

L. Philip Lounibos
Florida Medical Entomology Laboratory
University of Florida
Vero Beach, FL

Dr. Dorit responds:

Dr. Lounibos’s letter sheds further light on the intricate biology of the invasive vectors propelling the Zika outbreak in the Americas. As he points out, both the host preferences and the predominant habitats of the two mosquito species vary significantly in the different regions where they are found. Furthermore, the geographic distributions of the vectors and their areas of overlap also alter their feeding ecology. Taken together, the issues raised in this letter underscore the challenges inherent in both predicting and in controlling infectious outbreaks: As I point out in my column, every player in this outbreak—including the vectors—is in motion, adapting and evolving over both ecological and evolutionary timescales. As Dr. Lounibos cautions, the successful establishment in the Americas of the related flavivirus responsible for yellow fever is not a reassuring precedent as we look ahead.