Background: In 2007, two novel human polyomaviruses were reported, the Karolinska Institute polyomavirus (KI) and the Washington University polyomavirus (WU), both were discovered in respiratory tract samples from individuals with acute respiratory tract infections, and they were categorized among Polyomaviridae family.  Both viruses were detected in specimens from patients with respiratory tract disease on all continents suggesting a worldwide distribution. Serological studies have shown that similarly to BK and JC, infection with the new polyomaviruses KI, WU is common in the general population. Primary infection probably occurs early in childhood, as suggested by the seroprevalence in young people (<21 years of age), which is similar to that of adults. KI and WU polyomaviruses have been detected in respiratory samples from children and adult patients with acute respiratory symptoms from around the world. And some studies also found that there is a relationship between these two viruses and some other diseases.