There are plenty of viruses that still do something, but we don't know what it is, because the something is not immediately threatening to public health. For i

There are plenty of viruses that still do something, but we don't know what it is, because the something is not immediately threatening to public health. For instance, there is a chicken virus (SMAM-1) that unconditionally increases adiposity in the infected bird, even when the chicken is fed the same amount as inunfected chickens. SMAM-1 is zoonotic to humans. It also makes them fat. Several human adenoviruses are suspected of doing similar things. But they have not been studied extensively, because the general prejudice is that people become morbidly obese due to their own lifestyle choices, and therefore excessive adiposity is a condition that should be first-treated with lifestyle intervention, rather than applying evidence-based medicine. There are still a lot of nonscientific prejudices in general medicine. "Let's sequence all viruses in our patients," sounds a whole lot like "let's wash our hands before touching a new patient, so we don't spread diseases between them," which was once rejected by the experts as implausible hogwash.