The view through the mosquito net is blurry, but I can see the thick skin of grime on the leading edge of each blade of the ceiling fan as it slowly whirs around, keening alarmingly. This is how it was every summer when I visited my grandmother's house in southern India. While my cousins snore on the bed mats laid across the floor beside me, glistening bodies bathed in the warm night breeze, my sleeping mat is ensconced in a hot, gauzy cage. The mosquitoes descend from the darkened corners of the whitewashed room and perch menacingly on the taut netting, ready to exploit any flicker of movement from their prey within. It is hard to fall asleep knowing they are there, watching me, but eventually I drop off and my tensed body uncurls. They sneak into the gaps my protruding limbs create, and feast.

In the morning, all my hard work of trying to fi t in, to overcome the Americanness of my suburban New England life, has been undone, for my Indian cousins are smooth and brown while I am speckled with bleeding scabs. My grandmother vigorously pats talcum powder over my wounds, the white powder caking pink with congealed blood, as my cousins snicker. I don't understand how they escape unscathed while I am tormented. But incomprehension is part of the package of these childhood summers in India. Just outside my grandmother's house ragged families huddle in rubble along the road and use the train tracks as their toilet. They wave their sticklike arms in my face and moan woefully when we pass by on the way to temple, caricatures of beggars. One boy's leg has swollen to the size of a log, and is gray and pimpled, from some disease brought on by a mosquito bite. My grandmother tightens her grip on my hand. We give the children nothing. I can't understand this, either. When we get to the white marble temple, it is full of incense and golden statues encrusted with diamonds and rubies -- to my seven-year-old mind, the very picture of prosperity.

Part of me despises my estrangement, my incomprehension, the fact that I must sleep under the suffocating net and take the malaria pills while my cousins don't. But part of me is secretly glad. The boy with the swollen leg frightens me. The family who lives on the curb frightens me. India frightens me. These fears, for the girl who is supposed to be Indian but isn't, are unspeakable.

When no one is looking, I crush the mosquitoes' poised little figures with my palm and smear the remains on a hidden seam in the couch. Our Jain religion forbids violence of any kind. No eating meat. No swatting flies. My grandmother wears a mask over her mouth while she prays, to protect airborne microbes from inadvertent annihilation in her inhalations, and considers walking on blades of grass a sin. Meanwhile, there I am in the corner, cravenly pulverizing mosquito corpses behind my back, blood literally on my hands.

Back home in New England, the mosquitoes still bite, but there are no nets at night, no pills to take, no scary beggars on the side of the road. We shop for forgettable plastic trinkets at the mall. My fear and loathing of the mosquito are blunted into games of tag. My father calls himself Giant Mosquito, undulates his fingers like proboscises and chases me and my sister. It's scary, but fun-scary. We screech with glee and stampede through the house.

Thirty years later, on the S-shaped land bridge between the North and South American continents, I meet Jose Calzada. Calzada is a mosquito stalker of sorts, and I, the mosquito hater, have come to learn about the local mosquitoes and their exploits. A parasitologist from Panama City, Panama, Calzada spends his time rushing to the scene of disease outbreaks across the isthmus. The mosquito-borne parasite that causes malaria, Plasmodium, is one of his specialties.

It is April 2006. For most of the past century, there hasn't been much work in this field for people such as Calzada. Panama prides itself on being one of just a handful of tropical developing countries to have tamed its mosquitoes and nearly conquered malaria. American military engineers built a canal through Panama in the early 1900s, and forced malaria to retreat to the remote fringes of the country. Since then it has stagnated, primarily in its most benign incarnation, vivax malaria, which is rarely fatal.

But things have changed in recent years, and Calzada has agreed to show me some obscure signs. He emerges from the imposing Gorgas Memorial Institute, Panama's sole health research center. Clean-shaven and trim, Calzada has a slightly worried look in his eyes that is off set by high cheekbones suggesting a perpetual halfsmile. I wait while he meticulously changes out of his work clothes -- button-down oxford shirt and slacks -- and into a T-shirt and jeans. Climbing into my diminutive white rental car and tossing a baseball cap on top of his backpack in the backseat, he patiently directs me out of the labyrinthine metropolis. Navigating Panama City's congested streets, past shiny skyscrapers and packed cafes, is a task that challenges even my well-honed Boston driving skills.

After twenty minutes heading east out of the city, the road turns quiet. It's a lovely drive, with hills in the distance, verdant pasture and scrub unbroken save for a few elaborately gated houses set far back from the road. Colombian drug lords, Calzada says, by way of explanation. Another hour passes, and the road rises, a glittering lake coming into view, just visible through a tangle of jungle. As we near the water, the pavement ends, and we pull over.

Here, at the end of the road, is the town of Chepo. From what I can see, it consists of a wooden lean-to facing a sleepy roadside cafe. Two police officers amble out of the lean-to, which turns out to be a checkpoint. They take my passport and vanish, leaving Calzada and me to buy a cold drink at the near-empty cafe. As we sit, I can just make them out in the murk within the lean-to, inspecting the blue passport with great care, turning it over and over in their hands as if for clues to some baffling mystery.

Inspection completed, Calzada leads us on foot behind the road. The hillside is green and lush, with a slick red clay track leading to the crest. He heads up and I follow gingerly.

Excerpted from The Fever: How Malaria Has Ruled Humankind for 500,000 Years by Sonia Shah. Copyright 2010 by Sonia Shah. Excerpted by permission of Sarah Crichton Books / Farrar, Straus and Giroux, LLC. All rights reserved.

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