An Overview of Canine Distemper
Canine distemper is caused by the canine distemper virus (CDV). Prior to the arrival of canine parvovirus, CDV was unquestionably the most feared disease seen in domestic canines. This is a highly contagious, largely incurable, and often fatal disease that attacks the respiratory and gastrointestinal tracts, and, most devastatingly, the central nervous system (CNS).
Cases of canine distemper are much less common today due to the advent of effective vaccines, but puppies and even unvaccinated adult dogs are still highly susceptible to infection. Even with a conscientious vaccination program, some dogs still fall victim to this potentially fatal virus.
Why and how might my dog become infected?
Despite the fact that CDV particles are present in many environments, not every dog will become infected. This is because several factors influence the effectiveness of the virus. Host vitality (overall health of the dog, immune experience, vaccination status), virulence of the virus (the number of viral particles in a given area), and other environmental factors (stress, dry weather, cold weather) all interact and ultimately determine whether or not an individual dog will fall ill. Though the most important factors seem to be the immune level of the dog and the number of viral particles the dog is exposed to, if each factor is ‘just right’, a dog will become infected. When this occurs, a specific sequence of events is initiated as the virus attacks the body.
CDV travels about as aerosol particles and enters the body through the nose or mouth as the dog breathes. There is then a latent period of approximately 10 to 14 days during which the virus is replicating and spreading throughout the body, but no clinical symptoms have yet become visible. Once in the respiratory tract, the virus makes its way to the nearby lymph nodes in the neck. Once secure within the nodes, viral particles begin replicating and gradually spread through the lymphatic system, generally infecting all lymphatic tissue within 5 days. By the ninth day post infection the virus has invaded the blood, from which it will spread into the respiratory and GI tracts and eventually the CNS.
Canine distemper is estimated to be fatal in 50% of cases affecting adult dogs, and in 80% of cases affecting puppies. When the virus does prove fatal, death is usually a result of damage to the nervous system and ensuing complications such as seizures.
How will my vet reach a diagnosis of distemper?
Symptoms of distemper can be extremely variable depending upon the stage of the disease. The initial symptom of infection is fever, but this is easy to overlook and often goes unnoticed. Other classic early symptoms of distemper include significant eye and nose discharge, often accompanied or followed by depression, loss of appetite, nausea, vomiting, and diarrhea. Pneumonia is sometimes yet another side effect, but does not appear in all cases. Many dogs experience trouble with their vision as a result of CDV. Inflammation, lesions, and ultimately blindness due to swelling of the optic nerve may sometimes be observed. Symptoms indicating infection of the CNS include encephalomyelitis – simply put, an inflammation of the brain and spinal cord. It is this aspect of the virus that is the most deadly, as it often causes muscle incoordination, muscle spasm, seizure, partial or complete paralysis, and deterioration of mental faculties.
The early symptoms of distemper are similar to those exhibited by other diseases. If however you suspect your dog is exhibiting any symptom that might indicate infection with CDV, you should contact your veterinarian immediately. Diagnosis can be difficult but is possible and is based on a variety of factors including laboratory tests. Because distemper symptoms are so varied, there is no one test to determine whether or not your dog is infected. Rather, a wide range of procedures, when used together, may lead to a diagnosis.
Common respiratory side effects such as pneumonia may be detected by either x-ray or CT scan. Cerebrospinal fluid (liquid that surround the brain and spinal cord) can be examined for the presence of antibodies that would only be present if CDV were in the body. Similarly, immunofluorescent assays can detect the presence of viral antigens – immune system proteins that serve to fight viral invaders. A polymerase chain reaction (PCR) can be used to determine the genetic sequence of any virus present, but this is an extremely sensitive, difficult, and occasionally inaccurate technique. Finally, a microscopic examination of blood and tissue samples may detect the presence of inclusion bodies, cellular structures that indicate that CDV particles are present. None of these techniques can provide a definitive, question-free diagnosis. Generally a veterinarian will use laboratory procedures in conjunction with clinical observations and knowledge of the individual dog’s vaccination history in order to reach a diagnosis of distemper.
What are the treatment options for dogs with distemper?
Treatment procedures for dogs suffering from CDV are limited to a supportive capacity. A hospital stay may be necessary, as fluids and nutrients are often given intravenously and the trained veterinary staff is properly prepared to care for seriously ill animals. Treatments may vary between individual cases, but there are certain aspects that are considered vital.
The environment in which a sick dog resides must be kept clean, warm, and free of chilly drafts. An effort should be made to keep eyes and nose as free of discharge as possible. Certain medications may be prescribed to combat the effects of vomiting and diarrhea. As previously mentioned, the patient should be monitored closely for dehydration and may have to receive fluid and/or liquid nutrition intravenously. Dogs having difficulty with their vision may be administered glucocorticoid therapy in an attempt to prevent blindness. If the disease progresses to such a degree that neurological damage occurs, medicinal control of seizures and muscle spasms may become necessary.
Even if a dog survives and recovers from a bout with canine distemper, it should be noted that many animals continue to suffer long term effects. Enamel hypoplasia, or lack of tooth enamel, is a common affliction of CDV survivors. This deficiency, if untreated, causes severe tooth decay. A second long lasting effect of distemper is known as hyperkeratosis, which refers to an unnatural and uncomfortable hardening of the nose and foot pads. There is no easy, quick, or surefire cure for canine distemper.
How do I vaccinate my pet against canine distemper?
Vaccines are complicated substances and often raise many questions. For a brief introduction to vaccines and how they work, please goto An Introduction to the World of Vaccines.
Since the advent of effective vaccinations, CDV has become much less of a threat to domesticated dogs. This does not mean, however, that CDV is not a serious problem. Vaccination of your dog should not be considered an option – it is a must. Veterinarians usually administer the CDV vaccine as part of a combination which includes, among others, the parvovirus and coronavirus vaccines. These shots are given every 3-4 weeks from the time a puppy is 6 weeks old until he is at least 16 weeks of age.
How else can I help prevent the disease?
The most important step in preventing the spread of distemper is vaccination. Beyond that, however, certain steps may be taken to minimize exposure. Thankfully, the canine distemper virus is not as tough as the canine parvovirus and cannot survive for long outside the dog’s body. The viral particles may be killed by exposure to heat, sunlight, various detergents and soaps, and an assortment of chemicals. Any potentially infected dog should be isolated from other dogs. Once the sick dog has recovered or has left the home, pet owners should wait one month before introducing a new animal. Further, contaminated objects and areas may be disinfected using a 1:30 bleach-water solution.
Additional resources on the web:
Provides a brief and simple overview of the disease for pet owners.
Provides a slightly more in-depth description of canine distemper.
Merck Veterinary Manual
Intermediate-length article focused on the etiology, pathology and diagnosis of canine distemper.
International Veterinary Information Service
Article on canine distemper written for veterinary professionals.
For information on specific vaccines, visit the manufacturers' websites: