Canine Distemper

he infected dog typically infects other dogs via coughing infected respiratory secretions though the virus is shed in most other body secretions including urine. The virus enters the new host via the nose or mouth and promptly begins to replicate. Virus is engulfed by cells of the immune system called “macrophages.” The idea is that the virus will be engulfed, walled off within the cell and then destroyed by enzymes. Unfortunately for the new host, this process does not damage the virus as intended enabling the virus to use the macrophage as a means of transportation through the host’s body. Within 24 hours, the virus has traveled to the lymph nodes of the lung. By the 6th day, the virus has migrated to the spleen, stomach, small intestine, and liver. Fever is developing at this point.

By day 8 or 9 an important crux is reached in the timetable of infection. The host is mounting an immune response during this time and the outcome depends on how fast and how well this is accomplished. A strong immune response begins to clear the virus at this point and has eliminated all traces of virus with no symptoms of illness by Day 14. A weak immune response allows the virus to reach the “epithelial cells,” the cells which line every interface the body has with the outside world. The tender epithelial cells lining the chambers of the brain are infected as well. The host begins to get sick as the virus spreads but as the host’s immune response grows symptoms wane. This phenomenon accounts for the wide variability in symptoms; some dogs get only a few mild symptoms while others get a full lethal combination

After clearing from most internal organs, the virus is able to “hideout” for long periods of time in the nervous system and skin. Because of this phenomenon, callusing of skin or, much worse, seizures may occur long after the infection was thought to be cleared.

Most victims in the U.S. are puppies. (The colostrum suckled in the first day or so of life will provide them with a solid reflection of their mother’s immunity. This will have waned by age 16 weeks leaving the puppy vulnerable if vaccines have not been administered for further protection. In our society most mother dogs will have received some form of vaccination and thus be able to pass on at least some immunity and will have some ability to protect herself. In societies where vaccination is not common, distemper attacks all age dogs.)

Distemper is diagnosed based on a detailed history, physical examination, blood work and other diagnostic tests. In uncertain cases, cerebrospinal fluid may be analyzed. Most frequently, distemper is diagnosed by ruling out other causes of the clinical signs. The first sign of distemper is usually a watery discharge from the eye that may appear pus-like, followed by a nasal discharge, fever, vomiting, and diarrhea. Canine distemper was once referred to as the “hard pad disease” due to some cases causing the pads of the paws to harden. Some other signs and symptoms of canine distemper include:

• Coughing
• Lethargy
• Decreased appetite
• Calluses or a hardening of the footpads and nose
• Seizures or twitching
• Complete or partial paralysis in the last stages 

Dogs with signs of distemper are usually hospitalized for ongoing supportive care. Intravenous fluids and antibiotics are given to control infections, and other medications to control vomiting and diarrhea, convulsions and seizures may also be administered. The prognosis depends on the duration of the infection and the individual’s ability to stave off the infection. However, once stabilized, most pets recover without long term effects.

The best way to control this virus is by vaccinating and maintaining the booster schedule suggested by your veterinarian. Most comprehensive annual vaccines include a vaccine against the distemper virus. All puppies should be vaccinated by the time they are 5-6 weeks old and need to be boostered monthly until their immune systems are fully developed.