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).
The child is related to you as your son, daughter, stepchild, foster child, adopted child, brother or sister. He may also be a descendant of any of these relatives, such as a grandchild, nephew or niece. The child lived with you for more than half the year. The child was younger than age 17 on the last day of the year.