[ Reigen makes an 'ehhh' sound before continuing. ]

Kind of. Mostly. Spirits are certainly a product of humans. Things like urban legends can take on physical forms if enough people believe in them.

Not sure what you're implying by full-blooded, though. Spirits don't have bodies, if that's what you're asking. A human can be possessed by a spirit but it won't get into their blood. That would be weird.