Causes of Canine Distemper
Canine distemper is caused by a Morbillivirus from the family Paramyxoviridae. It is closely related to the measles virus and to the Rinderpest virus of cattle, and it now is referred to as the Canine Distemper Virus, or CDV. Most dogs are exposed to this virus either by inhaling respiratory secretions from an infected animal or by direct contact with infected saliva, urine or feces. Once that happens, the virus reproduces first in the dog’s respiratory tract and eventually spreads to the lymph nodes and through the lymph and blood circulation throughout its body, causing a condition called viremia. The canine distemper virus can infect the skin, gastrointestinal tract, urogenital tracts, central nervous system, or all of these areas, among others. Respiratory signs typically occur first, followed by gastrointestinal signs and in severe cases neurological signs, depending upon the status of the dog’s immune system. Infected dogs can shed the virus for several months after they become infected, whether they show clinical signs or not.
Distemper in domestic dogs can be prevented by timely vaccination of puppies starting at a young age (currently reported to be 6 to 8 weeks) and repeated every 3 to 4 weeks until 16 weeks of age, then boosted periodically. Your veterinarian can recommend an appropriate vaccination protocol for your dog, as these protocols tend to change as scientific research progresses. Keeping young dogs away from areas that are frequented by dogs of unknown vaccination status can also help prevent infection. Puppies should not be taken to dog parks or other places where many dogs visit until those puppies are fully vaccinated against distemper. Dogs who are properly vaccinated may still contract distemper under circumstances of extreme stress or when their immune systems are especially compromised, although that is uncommon.
Canine distemper is not considered to be transmissible to people, although some authorities report that humans can become infected with the canine distemper virus subclinically, which means that they do not exhibit or experience any clinical symptoms so they never know that they are infected. However, infected dogs shed the virus abundantly in respiratory and oral secretions, and viral particles are also prevalent in the urine and feces of infected animals. This infectious disease is highly contagious to other animals, especially young ones. Young dogs with signs of “kennel cough” may in fact have distemper, especially if their vaccination history is sketchy. Dogs diagnosed with distemper should be separated from all other dogs, especially healthy puppies, for several weeks even after the sick dog’s signs have resolved, because infected dogs can shed the distemper virus for several weeks after they appear to be well.