Severe enteritis caused by a small nonenveloped single-stranded deoxyribonucleic acid (DNA) virus that is resistant to inactivation and remains infectious in the environment for 5–7 months. First observed in dogs in 1976, canine parvovirus may have originated by mutation of a closely related parvovirus of cats or wildlife. The original virus was designated as canine parvovirus, type 2 (CPV-2); however, since its discovery the virus has undergone two minor genetic alterations, designated CPV-2a and CPV-2b. These alterations may have enabled the virus to adapt to its new host, replicate, and spread more effectively.