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).
Great grandfather to Grandfather to Father to you. Great grandfather's sister to Grandfather to Father to your cousin ( I am simply assuming that she had a son who had a son and then a son or daughter that is your cousin whom you are going to meet. Your cousin's father and your father were cousins, third cousins. Your cousin's grandfather and your grandfather were cousins, second cousins.