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).
What relationship to you is your great-uncle's daughter? Your great uncle's child is your parent's first cousin, and your first cousin once removed. What is the relationship of my second cousin's granddaughter to me? Your second cousin's granddaughter is your 2nd cousin twice removed. The once removed and twice removed refer to how many generations they are removed from your own.