This is not dust or a flying insect.
We have debunked many orb photographs over the years but have been unable to explain this one away.If the orb hadn't been seen with the naked eye, then it could possibly have been explained as camera glare or similar.
Instead, we are left with an unexplained supernatural phenomenon;one that cannot be explained rationally. Is it a 'spirit'? That is open to personal opinion. Whatever it was, it decided to be captured on photo footage.