Answer
Emerging disease refers to a disease which has been observed for first time. For example, COVID-19 is an emerging disease. On the other hand reemerging disease is the one which has been observed in past and then controlled. However, if it is observed again it will be called reemerging disease. For example SARS was observed in 2002-2003, if it is observed again it will be a reemerging disease.
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