9 CFR §93.320

Horses from or transiting through Central America and the West Indies shall be inspected as provided in § 93.306; shall be accompanied by a certificate and otherwise handled as provided in § 93.314; and shall be quarantined and tested as provided in § 93.308(a), (b) and (c): Provided, That any such horses that are found to be infested with fever ticks, Boophilus annulatus, shall not be permitted entry until they have been freed therefrom by dipping in a permitted arsenical solution or by other treatment approved by the Administrator.