The Blood-Sucking, Disease-Bearing Girl Next Door

[I had fun writing this essay for the William S. Pollitzer Student Travel Award with AAPA. Both undergraduate and graduate students are welcome to apply and respond to the year's prompt if they are attending the AAPA conference!]

Say you have a bag full of marbles. (Those in proverbial situations commonly do.) Now say you drop that proverbial bag of marbles, spilling its innumerable contents irretrievably across the kitchen floor. And say, too, that before dropping your own bag of marbles you’d met with your sister and mother and nephews and given ones to each of them, who’d then carried their new prizes to rooms all over the house before spilling their own, illustrative marbles. A mess, right? And one not too easy to contain.

Now imagine instead that the marbles are Aedes aegypti individuals, mosquitoes known to carry Zika and Chikungyuna viruses, and Dengue and yellow fevers, among other diseases, that the bags you and your loved ones, now millions of travelers across the globe, held close are loose but historically-restrictive climactic envelopes, that the rooms in your home are Central and South America, Polynesia, Texas and Florida. Is this metaphor wearing off? Is it clear first that this latter ‘mess’ is more severe and assuredly less-cartoonish than a houseful of marbles? Cross any resilient and rapidly-reproducing species with an unprecedented opportunity for geographic expansion and the result is simple: an unprecedented expansion of that species.

With climate change and increasing globalization, A. aegypti can be expected to do just that: to expand and to carry with it globally increased risks of contracting mosquito-borne diseases. Take Zika as one example of A. aegypti’s globetrotting prowess as a disease vector, the virus infamous for its potential to cause birth defects, such as microcephaly, in the babies of infected mothers. First diagnosed in 1954 in Nigeria, Zika virus rested in relative obscurity until 2007 when an outbreak infected over seventy-percent of the Pacific Ocean’s Yap Island residents. From there it took to Gabon, French Polynesia, New Caledonia, Vanautu, and the Cook, Solomon, and Easter Islands before making a jump to the western hemisphere, to Brazil, in 2015. By late 2015, Zika was already discovered to have been locally-transmitted by A. aegypti in North America, where estimated rates of Zika-carrying adult mosquitos in the Chiapas region of southern Mexico numbered 5-17% [1]. By August 2016, local cases were reported from 45 Central and South American and Caribbean countries and territories. The United States numbered among these: the CDC confirms 227 locally-transmitted and 5,335 cases from U.S. travelers to-date [2]. These locations, while worldly, are perhaps not surprising for a tropical-subtropical insect to call home—all local cases in the United States after all have been restricted to the sunny climes of Texas and Florida. But what if formerly hostile locations become both more accessible and less hostile? Should we be adding Capitol Hill to our new travel advisory list?

Discovery of A. aegypti individuals in the Capitol Hill neighborhood of Washington, D.C. raises concern that climate change truly has had and will continue to have a hand in A. aegypti’s spread [3]. A. aegypti’s range in the United States was formerly thought to be restricted to the 10°C winter isotherm that left South Carolina as A. aegptyi’s northernmost limit: A. aegypti were also not thought to be able to survive cold, wintering months. Yet there, decidedly north of South Carolina, they were—and year-round, presumably ringing in the warmer months following cold, dormant periods as larvae underground. A map estimating the current risk of Zika-carrying A. aegypti using meteorological variables and human traffic into the United States reads like a paper towel that has only just been dipped into a tray of ink: southeastern states are most at risk and at-risk year-round while A. aegypti leaks as far north as New York in warmer months [4]. This range will push more northward, more westward and will extend farther into winter months as rising temperatures, growing populations, and increasing global connectivity allow it to. And reliably with it, we can assume, mosquito-borne diseases will follow.

Remember that Zika virus is not the only pathogen carried by A. aegypti. Remember, too, that mosquitoes are not the only invasive species being given ecological openings by climate change. And, finally, remember most of all that the United States is not the only country of concern, that poverty and urbanization exacerbate the problem of mosquito-borne diseases [5], that we will not be among those most impacted. This isn’t a problem bug spray is going to fix.
 
[1] Guerbois, M., Fernandez-Salas, I., Azar, S. R., Danis-Lozano, R., Alpuche-Aranda, C. M., Leal, G., ... & Del Río-Galván, S. L. (2016). Outbreak of Zika virus infection, Chiapas State, Mexico, 2015, and first confirmed transmission by Aedes aegypti mosquitoes in the Americas. The Journal of Infectious Diseases, 214(9), 1349-1356.
[2] Zika Virus. (2017, December 21). Retrieved December 31, 2017, from https://www.cdc.gov/zika/reporting/case-counts.html
[3] Lima, A., Lovin, D. D., Hickner, P. V., & Severson, D. W. (2016). Evidence for an overwintering population of Aedes aegypti in Capitol Hill neighborhood, Washington, DC. The American Journal of Tropical Medicine and Hygiene, 94(1), 231-235.
[4] Monaghan, A. J., Morin, C. W., Steinhoff, D. F., Wilhelmi, O., Hayden, M., Quattrochi, D. A., ... & Scalf, P. E. (2016). On the seasonal occurrence and abundance of the Zika virus vector mosquito Aedes aegypti in the contiguous United States. PLoS Currents, 8.
[5] Imperato, P. J. (2016). The convergence of a virus, mosquitoes, and human travel in globalizing the Zika epidemic. Journal of Community Health, 41(3), 674-679.

Image Credit: Center for Disease Control