Canine distemper virus (CDV) causes a highly contagious disease of dogs and also affects other species such as the fox, coyote, wolf, ferret, skunk, and raccoon. The incidence of disease is greatest in young dogs three to six months of age. Young dogs are most susceptible because the protection against distemper that is passed on from mother to newborn has decreased or disappeared by 9 to12 weeks of age.
Distemper is caused by a virus similar to the one that causes measles in people. It is transmitted through the air via droplets originating from many bodily fluids of an infected animal. Because the virus does not affect people or cats, there is no concern for dogs transmitting it to these species.
Different stages of the disease are associated with various clinical signs, usually involving some combination of the respiratory and/or gastrointestinal tract signs in the early stages, and the nervous system several weeks later. Not all stages occur in all dogs. Distemper is much less common than it was years ago, prior to the introduction of the distemper vaccination. The prognosis for dogs with distemper ranges from good to guarded. Some patients recover; some patients recover but have additional manifestations of the disease later in life; some dogs die from the disease or have such severe persistent signs that they must be euthanized.
Several diseases and disorders can appear similar to canine distemper. Kennel cough, or infectious tracheobronchitis, is a contagious respiratory disease of dogs that is manifested by coughing. This is a transient disease, and most dogs recover without severe complications.
The respiratory form of canine distemper must be differentiated from the following:
Pneumonia due to other infections (bacterial, fungal) can present similarly to dogs with distemper.
The gastrointestinal (GI) form of canine distemper must be differentiated from the following:
Other GI viral diseases including parvovirus and coronavirus
Bacterial enteritis including Campylobacter, Salmonella and Clostridia
Protozoal infections, specifically, Giardia
Ingestion of foreign bodies and toxins
Any non-infectious disorder that causes vomiting and diarrhea in dogs
The central nervous system (CNS) form of canine distemper must be differentiated from the following:
Granulomatous meningoencephalitis is a progressive, inflammatory disease of the central nervous system of dogs. Many signs seen in this disorder may mimic the neurologic form of canine distemper.
Protozoal encephalitis is an inflammation of the brain, caused by one of the protozoal organisms (neosporosis, toxoplasmosis).
Cryptococcosis is a systemic fungal infection that affects particularly the respiratory and neurologic systems.
Lead poisoning commonly produces clinical signs that involve both the gastrointestinal tract and nervous system.