I would get that head down quickly. Looks like you have imported something with the skull to me. I would soak the skull in boiling water with bleach in it. Outside the house. Then let it drip dry. I would then swill some acetone around in the skull, drip dry again and freeze it for at least a month. The horns I would leave outside with some acetone soak cotton wool in the ends. Then pour some into the horns and then tip out and then leave in a shed to dry out.
I certainly would get it out of the house straight away before infects the whole house.