The prevalence of BK viruria was 22 and 55 % in adult patients with multiple sclerosis [28] who received Natalizumab (an α4-integrin monoclonal antibody (mAb)) and those with inflammatory bowel disease [29] some of whom received Infliximab (an anti-tumor necrosis factor alpha (TNFα) chimeric mAb) and Adalimumab (anti-TNFα human mAb), respectively. Here, TNF is linked to multiple sclerosis.