Disease risks for dogs in social settings Canine distemper. Canine distemper is caused by a very contagious virus. ... Canine influenza ("canine flu" or "dog flu") Canine influenza is caused by the canine influenza virus. ... Canine parvovirus ("parvo") ... External parasites (ticks, fleas and mange) ... Heartworms. ... Leptospirosis.