Polyomavirus is a group of small, non-enveloped viruses that can infect various animals, including humans. They are known for their ability to cause tumors in certain conditions, particularly in immunocompromised individuals. The most studied types include JC virus and BK virus, which are often found in the human population without causing symptoms in healthy people. These viruses are typically spread through bodily fluids, such as urine, and can remain dormant in the body for long periods. In some cases, they may reactivate and lead to health issues, especially in people with weakened immune systems, making ongoing research into Polyomavirus important for understanding its effects on human health.