On Jul. 8, 2003, the U.S. Centers for Disease Control and Prevention (CDC) responded to U.S. outbreak of mpox, the first human mpox outside of Africa. Scientists at the Marshfield Clinic in Marshfield, Wisconsin, recovered a virus resembling a poxvirus from one of the first patients and the patient’s pet prairie dog.

CDC lab tests ‘including several PCR-based assays and gene sequencing’ confirmed that the agent causing the illnesses was mpox virus. Investigators determined that a shipment of animals from Ghana, imported to Texas on Apr. 9, 2003, introduced mpox virus from the West African genetic group (clade) into the U.S.