Fever can support the immune system's attempt to gain advantage over infectious agents, such as viruses and bacteria, and it makes the body less favorable as a host for replicating viruses and bacteria, which are temperature sensitive. Infectious agents are not the only causes of fever, however.
Your sister's grandson is your great nephew. You are his great aunt (if you are a woman) or his great uncle (if you are a man).
Well it's likely true but you should assume she's related. My Mothers Grand Mother was something like 4th or 5th in line for the Throne and I assure you, everyone around them from the ones folding their socks to the Groom of the Stool is a Cousin.