Make sure you're sitting down for your daily dose of health news: NPR noted that scientists have discovered 43,381 unknown viruses in sewerage water sampled in three cities (Pittsburgh, Barcelona and Addis Ababa). For perspective: science today has classified only about 3,000 known viruses. You can take solace in the fact that about 90 percent only infect bacteria or plants--not humans. But you're still allowed to panic about the more than 4,000 viruses that might come after you--especially if you saw Contagion. The study, which appeared in the journal mBio, however, concludes that knowing what's out there is the best defense from eye-melting superbugs:

At this time, virology is focused on the study of a relatively small number of viral species. Specific viruses are studied either because they are easily propagated in the laboratory or because they are associated with disease. The lack of knowledge of the size and characteristics of the viral universe and the diversity of viral genomes is a roadblock to understanding important issues, such as the origin of emerging pathogens and the extent of gene exchange among viruses.

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