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).
Jessica Bell (English dub) Amalia Sheran Sharm (or Amalia for short) is one of the main characters of the Wakfu: The Animated Series. She is the princess of the Sadida Kingdom, but isn't terribly fond of her royal duties and would much rather go out adventuring, often dragging a bemused Evangelyne in tow.