A multi-million dollar effort to produce a test to guide treatment for a potentially lethal skin cancer recently fell apart after the scientific investigator discovered that the commercial antibodies he was using were unreliable. Cultura RM Exclusive/Peter Mulle/Getty Images hide caption

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Cultura RM Exclusive/Peter Mulle/Getty Images

A blood test developed by Harvard researchers checks for evidence of past infection with more than a thousand strains of virus, from about 200 virus families. The swine flu virus shown here, A/CA/4/09, rarely infects humans. C. S. Goldsmith/CDC hide caption

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C. S. Goldsmith/CDC

How Many Viruses Have Infected You?

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