Canine distemper is a contagious, often fatal, multisystemic viral disease that affects the respiratory, gastrointestinal, and central nervous systems of dogs. Distemper is caused by infection with the canine distemper virus. Canine distemper virus occurs among domestic dogs as well as many wild species, including raccoons, skunks, and foxes. The development of an effective vaccine in the early 1960s led to a dramatic reduction in the number of infected domestic dogs, occuring now now only as sporadic outbreaks.
Young puppies between 3 and 6 months old are most susceptible to infection and disease and are more likely to succumb to the disease than infected adults. Non-vaccinated older dogs are also highly susceptible to infection and disease. Non-vaccinated dogs that have contact with other nonimmunized dogs or with wild carnivores have a greater risk of contracting canine distemper.
Dogs infected with canine distemper virus, shed the virus through bodily secretions and excretions, especially respiratory secretions. The primary mode of transmission is exhaled airborne viral particles that dogs breathe in.
Dogs in recovery may continue to shed the virus for several weeks after symptoms cease, but they no longer shed the virus once they are fully recovered. It is possible for humans to contract an asymptomatic (subclinical) canine distemper infection. Anyone who’s been vaccinated against measles (a related virus) is protected against CDV as well.
Macrophages (white blood cells that ingest foreign disease-carrying organisms, such as viruses and bacteria) carry the inhaled virus to nearby lymph nodes where it begins replicating (reproducing). It spreads rapidly through the lymphatic system and infects all the lymphoid organs within 2 to 7 days. By days six to nine, the virus then begings to invade the central nervous system and lungs.
Early symptoms of canine distemper include fever, anorexia, and mild eye inflammation that may only last a day or two. Signs become more serious and noticeable as the disease progresses.
The initial symptom is fever (103ºF to 106ºF), which usually peaks 3 to 8 days after infection. The fever often goes unnoticed by the owner and may peak again a few days later. Dogs may experience eye occular and nasal discharge, depression, and loss of appetite (anorexia). After the fever, signs vary considerably, depending on the strain of the virus and the dog’s immunity.
The set of clinical signs that dogs infected with canine distemper virus may show involve multiple organ systems and include:
Ataxia (muscle incoordination)
Hyperesthesia (increased sensitivity to sensory stimuli, such as pain or touch)
Myoclonus (muscle twitching or spasm), which can become disabling
Paresis (partial or incomplete paralysis)
Progressive deterioration of mental abilities
Progressive deterioration of motor skills
Conjunctivitis (discharge from the eye)
Fever (usually present but unnoticed)
Pneumonia (cough, labored breathing)
Rhinitis (runny nose)
These symptoms are often comlicated by secondary bacterial infections. Dogs almost always develop encephalomyelitis (an inflammation of the brain and spinal cord), the signs of which are variable and progressive. Most dogs that contract distemper, die from neurological complications including the following:
Seizures that are unique to distemper, are sometimes referred to as a “chewing gum fits” because the dog appears to be chewing gum.)
Many dogs experience occular disease:
Inflammation of the eye (keratoconjunctivitis, inflammation of the cornea and conjunctiva, or chorioretinitis, inflammation of the choroid and retina)
Lesions of the retina (the innermost layer of the eye)
Optic neuritis (inflammation of the optic nerve which leads to blindness)
Two relatively minor conditions that often become chronic, even in dogs that recover are:
Enamel hypoplasia (inadequate production of enamel to protect the teeth – distemper kills the cells that make enamel)
Hyperkeratosis (thickening and subsequent hardening of the skin of the foot pads and nose)
In utero infection of fetuses is rare, but can occur. This may lead to spontaneous abortion, persistent infection in neonates, or the birth of normal looking puppies that rapidly develop symptoms and die within 3 to 6 weeks.
Roger L. Welton, DVM
Founder and Chief Editor, Web-DVM.net
President, Maybeck Animal Hospital