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).
My Second Cousin removed a Guide to understand relationships Your uncle is the brother of your father or mother. Your aunt is the sister of your father or mother. Your great uncle (or grand uncle) is the brother of your grandfather or grandmother. Your great aunt (or grand aunt) is the sister of your grandfather or grandmother. Your great-great uncle is the brother of your great-grandfather or great-grandmother. Your great-great aunt is the sister of your great-grandfather or great-grandmother. Your first cousin is the child of your aunt or uncle. Your second cousin is the grandchild of your great aunt or great uncle.