If Thomas Cropper, a public-health veterinarian at Lackland Air Force Base, in San Antonio, Texas, thought about Chagas disease at all, he thought about it as a Central and South American problem. Named after the Brazilian physician who described it, in 1909, Chagas is a classic—one might say egregious—example of a neglected tropical disease. It is caused by the protozoan parasite Trypanosoma cruzi, which is delivered to its host by kissing bugs, known formally as triatomines. The bugs are bloodsuckers—their nickname comes from their penchant for biting near the eyes or mouth—and they can swell to the size of grapes as they feed, causing them to defecate and leave the parasite behind to make its way into the host’s bloodstream. A gross and not particularly efficient mode of transmission, it’s still good enough to have kept Chagas going since pre-Columbian times. According to the World Health Organization’s shifting estimates, between six and seven million people in Latin America are currently infected. If you’re infected but don’t have symptoms, you’re likely to find out only after donating blood. If you do have symptoms, you’re probably in trouble. About a third of Chagas patients develop a chronic form that leads to heart damage and failure.
Cropper specializes mainly in zoonoses—diseases transmissible from animals to humans—and in keeping service members away from them. Not long after he arrived at Lackland, in 2008, he learned that a military working dog had developed heart problems while deployed in Kuwait. The dog was returned to Lackland, the home of the Department of Defense’s canine school, and confirmed positive for Chagas. A study of all the working dogs on base, in fact, found that about eight per cent had antibodies against T. cruzi. Many never developed symptoms at all, but young pups would sometimes drop dead without warning. Cropper began asking about Chagas and what the risks might be for humans. “What else are these stupid bugs feeding on?” he wondered. This turned out to be a somewhat urgent question, because Lackland is where about thirty-five thousand Air Force and National Guard recruits are trained every year, often outdoors. The base encompasses a vast, cactus-strewn wilderness with populations of wood rats, armadillos, skunks, opossums, and other easy targets for a kissing bug.
Cropper called in an entomologist, Walter Roachell, and a microbiologist, Candelaria Daniels, from the Army Public Health Command at Joint Base San Antonio. Roachell found five species of kissing bug at Lackland, some in the nests dug by wood rats in the bottoms of cacti. A training instructor who accompanied Roachell claimed that he’d never before seen one of the bugs, even though certain species are distinctive—pretty, even—with their folded wings encircled by what could be described as a striped skirt. “I looked down and pointed out one crawling between his feet,” Roachell told me. Daniels, meanwhile, sought to determine the bugs’ infection rates. More than half of them, her analysis revealed, carried T. cruzi. They were eating a lot of things—wood rats, armadillos, even rattlesnakes. And, more alarmingly, nearly thirty per cent tested positive for human blood. “They were indeed feeding on people,” she said. Cropper had vegetation cut back, insecticide sprayed, and treated bed nets installed where trainees slept, and similar measures were taken around the kennels. At one point, a routine blood donation by an airman, who had neither a history of travel to Latin America nor a mother likely to have transmitted the disease to him in utero, turned up positive. He remembered suffering a swelling around his eye—one early sign of a Chagas infection—which he blamed on dirt. It “may have been feces from the kissing bug,” Cropper said, but no one was really sure.
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