Canine distemper is caused by a Morbillivirus, closely related to the virus causing measles in humans. It is most commonly seen in puppies 3 to 6 months old and in young un-vaccinated dogs. Puppies can be infected in-utero when the virus crosses the placental barrier between the mother and fetuses. This often causes abortion or a still-birth. If the puppies survive, they may show signs of central nervous system damage such as tremors, wobbliness, and seizures, which may worsen as the puppy ages.
The distemper virus is very contagious. It is passed from dog to dog through close contact from secretions such as urine, feces, saliva, respiratory and occular discharge. For example, the infected dog sneezes, spreading the virus to other dogs. The virus establishes itself in the nasal passages of the new dog. It then multiplies and spreads throughout the body, damaging cells from the eyes, lungs, and intestinal tract. It also damages the dog’s immune system and can spread to the nervous system causing further damage.
Symptoms of distemper virus include: anorexia, fever, discharge from the nose and eyes, pneumonia, vomiting and diarrhea. It can also infect the paw pads causing a hard scaley thickening. Damage to the brain and spinal cord causes neurologic signs. This happens in approximately 50% of infected dogs 2-3 weeks after infection. Often, these dogs are responding well to treatment when the symptoms develop. This causes seizures, both epileptic and isolated to the head. It also causes weakness, paralysis, loss of coordination, and involuntary twitching of the legs. Most dogs developing neurologic symptoms are either euthanized or die from the virus.
Distemper virus is difficult to diagnose. One way is for a diagnostic lab to preform a titer, which measures the level of distemper antibodies in the dog’s blood and tissue. A PCR can also be done, which looks for the virus itself, but neither of these methods is foolproof. Distemper viral inclusions can also be seen in blood cells on a microscope for 2-9 days after the animal is infected, but may not be present anymore when the dog begins to show symptoms.
Treatment of distemper virus is strictly supportive, as there is no known cure for the disease. It includes intravenous fluids, antibiotics to help with any secondary infections, anti-seizure medications, anti-vomiting and diarrhea medications, as well as treatments to control any additional symptoms. An infected dog will continue to shed the virus for 60-90 days post infection.
Prevention is the best method to guard against this devastating disease. Puppies should receive vaccinations starting at 6-8 weeks of age when the mother’s antibodies passed to the puppy have worn off. Boosters should be given every 2-3 weeks until the puppy is 14-16 weeks old. The vaccine can then be boostered annually or according to the veterinarian’s guidelines. Often puppies are given a human measles vaccine, which will stimulate the production of distemper antibodies received from the bitch. It is important to remember that no vaccine provides 100% protection, but the protection it does supply is better then none at all.
Nelson R and Couto C. G. Manual of Small Animal Internal Medicine. St Louis Mo: Mosby, 1999
