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).
*** Just as your sister/brother s children are your children s cousins, addition is related to subtraction via the term inverse property. Subtraction is the inverse property of addition. In other words, subtraction is the opposite of addition. We can undo the work of addition by subtracting.