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).
Children of your FIRST COUSIN'S children, are your FIRST COUSINS, TWICE REMOVED. So, your FIRST COUSIN'S son is your FIRST COUSIN, ONCE REMOVED. And your FIRST COUSIN'S son's, son's daughter is..........your FIRST COUSIN, THREE TIMES, REMOVED. Thus, your SECOND COUSIN'S child is your SECOND COUSIN, ONCE REMOVED.