There had been concern expressed by the Council what when visiting other worlds, Earth especially, Eileen could bring back human type viruses and illnesses but, to date, this has not happened.
Youngsters in the Kingdom have a series of jabs against human diseases when still at school but there isn't anything available anywhere that would protect them from a curse spell. They are also expected to use their common sense if they come across gingerbread houses covered in sweets. Not only are they warned of the dangers of witches using this as a device to snare children (whom she intends to cook), but the perils of diabetes, obesity and tooth decay are also emphasized. The result has been nobody goes near a gingerbread house (much to the annoyance of the witch who originally patented the idea).
Humans are despised by the magical world for its warlike qualities and our capacity for polluting anything. Illnesses just stress how weak we are in the eyes of magical beings generally.