The Worst Animal in the World
For about a week this past September, I adopted a wellness routine that—at the time—felt like neurotic overkill. I didn’t bother with masks or hand sanitizer; back then, the virus we now know as SARS-CoV-2 was still presumably nestled in the warm body of an unknown animal. Instead, each morning, I spritzed my arms and legs with picaridin, a chemical repellent meant to ward off parasitic bugs. Then I covered myself with one of several increasingly crusty sets of khaki pants and long-sleeved shirts that I had infused with the insecticide permethrin. Only then, force field up, would I venture outside.
I had come to Dakar, Senegal, to get close—but not too close—to Aedes aegypti, a globally invasive mosquito that is arguably the worst animal in the world. The species carries yellow fever and dengue, both of which can cause more severe disease in young adults than SARS-CoV-2; Zika virus, which can lead to birth defects; and chikungunya virus, which can leave victims with debilitating joint pain.
Unlike viruses that travel person-to-person, most of these pathogens can spread only in places where mosquitoes live. Then again, aegypti’s range is immense. All told, her bites—and only females bite—cause an estimated 400 million infections each year, which means that several dozen people have been infected in the time it took you to read this sentence. In 2019, when the World Health Organization compiled a list of threats to global health, dengue got a whole slot to itself. Zika showed up in another slot, sharing billing with Ebola, SARS, and “disease X,” the prospect of some then-unknown pathogen with epidemic potential.
In Senegal, my own illusion of invulnerability lasted until I met Mawlouth Diallo, a medical entomologist from the Pasteur Institute in Dakar. Wearing a matching blue kaftan set, he sat with me in my hotel lobby for more than an hour, earnestly explaining his team’s mosquito research in smooth, French-accented English. Finally, I had to ask a nagging, basic question.
“Sitting here, right here,” I said, gesturing to the air-conditioned lobby, “where is the nearest Aedes aegypti?”
Diallo seemed confused at the question. “Where?”
“Like, could we go find some of them outside right now?”
“No, it is inside,” he said, then laughed out loud at the expression on my face. “For sure, aegypti is inside the hotel.” When dengue broke out in Dakar in 2009, the city’s Lebanese population was hit the hardest. One reason, Diallo said, was that mosquitoes and wealthy foreigners are both drawn to luxury indoor environments. In this lobby, he said, the best place to find Aedes aegypti would be the flowerpots.
I laughed with him, albeit less easily. Of the 3,000-plus mosquito species alive, most are is different. Whether in Rio de Janeiro, New Delhi, or Miami-Dade County, it will breed in clean water supplies, it will come indoors, it will make a beeline toward human odor, and it will bite when the sun is up, circumventing bed nets that protect at night. Masks to prevent the spread of COVID-19 won’t make a difference. Neither will staying at home, unless you live in a closed, air-conditioned house. No other mosquito is so perfectly suited to live with, and on, human beings.
