Amoeba threatens global health
Naegleria fowleri amoebas, like these, can glom onto nerve endings in the nose of an exposed individual and motor along them into the brain
Amoebas blob-shaped microbes linked to several deadly diseases contaminate drinking-water systems around the world, according to a new analysis. The study finds that amoebas are appearing often enough in water supplies and even in treated tap water to be considered a potential health risk. A number of these microorganisms can directly trigger disease, from a blinding corneal infection to a rapidly lethal brain inflammation. But many amoebas possess an equally sinister if less well-recognized alter ego: As Trojan horses, they can carry around harmful bacteria, allowing many types to not only multiply inside amoeba cells but also evade disinfection agents at water-treatment facilities. Even though recent data indicate that amoebas can harbor many serious waterborne human pathogens, U.S. water systems don't have to screen for the parasites, according to study coauthor Nicholas Ashbolt of the U.S. Environmental Protection Agency's National Exposure Research Laboratory in Cincinnati. He coauthored a study of amoebas' "yet unquantified emerging health risk" posted online December 31 in Environmental Science & Technology. He and Jacqueline Thomas of the University of New South Wales in Sydney analyze data from 26 studies conducted in 18 countries. All had identified amoebas in drinking-water systems. Some reports had focused on measurements at treatment plants, others in exiting water; some even extracted the parasites from tap water. Indeed, among 16 studies that looked for tap-water contamination, 45 percent reported finding amoebas. In 2003, Francine Marciano-Cabral of Virginia Commonwealth University in Richmond and her colleagues identified one species of amoeba that is directly lethal Naegleria fowleri in water throughout the plumbing of an Arizona home where two young girls had recently died. The amoeba explained the girls' fatal encephalitis, a brain disease. "We suspect they got it from submerging in the bathtub," Marciano-Cabral says. The family's private water supplies had not been chlorinated, a disinfection process that can limit amoeba contamination. Thomas and Ashbolt reviewed six studies that together included data from 16 different water-treatment plants and probed for sources of the amoebas that the studies had turned up. Five of those studies reported finding a high prevalence of the parasites in anywhere from 75 to 100 percent of the surface waters, such as rivers, that were sampled. After water treatment, often using carbon filtration or chlorination, contamination levels dropped somewhat, to fewer than 50 percent of water samples. In general, the new analysis points out, water treatment appears to reduce amoeba concentrations to a tenth or one-hundredth of starting concentrations, "but breakthrough events do occur and release potentially high numbers of free-living amoebae" roughly 110 of the parasites per liter into drinking-water distribution systems. Source: Science News
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