Student or Learner
The word casualty is used to refer to people who are hurt or killed in an accident or fight. Then can I use it to describe those who died because of the extreme weather or an epidemic? For example, the casualties in the heat wave are at least 10. Or there are more than 20 casualties in the epidemic. Are they correctly used here?
Yes, you can use the word, but they are casualties of the heat wave/epidemic.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.