We are all Russian nesting dolls: Our intestines house many bacteria, which house many viruses. These so-called bacteriophages are likely as important for our health as the bacteria they live in.
Lisa Brown for NPR
France has banned imports of live pigs and other products from the U.S. to keep out a virus that has killed more than 4 million pigs in the U.S. Here, young pigs look out of a pen at a North Dakota hog farm in a 2005 file photo.
This electron microscope image provided by researchers shows a section of a Pithovirus particle, dark outline, inside an infected Acanthamoeba castellanii cell.
Julia Bartoli, Chantal Abergel/AP