Virus-Disease Links Are Hard to Forge
By Douglas Steinberg
If genomics is glitzy nowadays, virus research is, well, gritty. Its latest heyday, when HIV was shown to cause AIDS, only masked its true nature. Associating viruses with diseases has always been particularly difficult and labor intensive. Cause-and-effect relationships are maddeningly elusive.1
Consider the following two questions: Does infection by mouse mammary tumor virus (MMTV) or a human homologue lead to human breast cancer? And does human herpesvirus 6 (HHV-6) contribute to multiple sclerosis?
These questions seem to have little in common. Discovered in the 1930s,2 MMTV is a retrovirus known to cause breast cancer by inserting itself into the genome and changing gene-expression patterns, albeit in mice, not humans. Identified 14 years ago,3 HHV-6 is a DNA virus that infects almost all people. Its link to multiple sclerosis, however, is...