Mo. Rev. Stat. § 322.030: Duty of owner or person in charge to kill dog or have immunized.

Whenever any dog has been bitten by, fought with, or has been substantially exposed to any dog affected with rabies, it shall be the duty of the owner, or person in charge thereof, forthwith to kill such exposed dog or have it immunized against rabies at the owner's or custodian's expense, by the administration of antirabic virus by a licensed veterinarian.