CHICAGO (Reuters) - An icky parasite that is a major source of tummy trouble for young children and nature lovers appears to have been infecting mammals for a very long time, U.S. researchers said on Thursday.
Giardia lamblia is one of the most common human parasites in the United States, causing more than 20,000 intestinal infections each year.
A complete genetic sequence of this parasite now suggests it had ancestors reaching back more than a billion years.
"We think it is deep in the evolutionary tree," said Hilary Morrison, of the Marine Biological Laboratory in Woods Hole, Massachusetts, whose study appears in the journal Science.
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