Shingles is caused by the same virus as chickenpox, so the illnesses could be related if your dad and cousins had come into contact. However, it’s also possible that the timing is just coincidence. Most people get chickenpox as a child, and after you’ve got better the virus stays in your body in a dormant form. Usually your immune system keeps it in check, but sometimes it can be reactivated and go on to cause shingles. It’s not known how or why reactivation might occur, but it’s thought to be related to a dip in your natural defences – for example, if you’re stressed.