There's no consensus on that in what Horus is concerned. Horus' stories, especially early ones don't make him a miracle maker. Also, it's not clear whether he was given birth to without Osiris' semen. So, I'd like the source.
The same goes for Mithra. The Iranian Mithra is more like the Christian Peter or the Egyptian Anubis in Duat.
Zoroastrianism has a messiah figure called Saoshyant. Later concepts say there might be three of them born by maidens.
The Mithra from the Roman spinoff religion of Indo-Aryan Mithra, called Mithraism, was born from a rock, much like Adam. Mithraism was more of a secret order religion, masonry if you will, a syncretism between Roman (rip of Greek mythology), Judaism-Christianity among others.
Like Christian sects spawned from Gnosticism, these movements were usually secretive and considered satanic.