Maggots can be a hazard to people and animals if they are ingested or if they get on the body. It is possible for maggots to infest living tissue in a condition called Myiasis.
Myiasis does not occur very often in the United States; instead it is a problem that exists mainly in tropical countries in South America and Africa. While Myiasis may pose a risk to people, it is commonly used in medicine in order to deal with the rotting flesh on wounds. The maggots used in these procedures have been sterilized and don't have the risks involved with wild maggots. Wild maggots consume rotting matter and various toxins, which if ingested by humans, could cause serious illness.