Word: protozoans
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Dates: during 1990-1999
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...culprit, test results show, is a tiny parasite with a big name: cryptosporidium. The oocysts (parasite versions of eggs) of this pesky protozoan can be removed only through filtration. Unlike bacteria, they are not readily killed by chlorine. Furthermore, the tests that water-purification plants routinely rely on to detect biological contaminants do not pick up the presence of cryptosporidium. What makes the parasite especially nasty, explains microbiologist Dean Cliver of the University of Wisconsin, Madison, is that the oocysts do not hatch in water -- in this case Lake Michigan water -- but remain dormant until they are swallowed by some...