Canine Distemper

Distemper is a highly contagious disease affecting dogs and wild carnivores, and is caused by a paramyxovirus. It has been very rare since 1960, when a vaccine was developed, but there are periodic outbreaks.

Distemper affects dogs of all ages, although different dogs have varying susceptibility. Dogs usually become infected by direct contact, inhaling the virus, which enters through the respiratory tract. After the virus enters the body, it multiplies in the tonsils and bronchi, then spreads throughout the body in about eight days. From this point, the disease can develop in three different ways. In about half of all dogs, the immune response developed after the infection is adequate and the virus disappears. These dogs recover after displaying only a few mild symptoms. In other dogs, however, the immune response is inadequate. These dogs have the characteristic symptoms of the disease. Finally, in a minority of dogs, apparent recovery takes place, but the dogs have nervous symptoms a month later.

The most classic form of this disease develops as follows. The incubation period lasts three to seven days, during which the dog displays no symptoms. Then the virus spreads through the dog's body and a fever of 40°C is observed, with a yellow discharge from the eyes and nose and sometimes, small pustules on the abdomen.

This stage lasts two to three days and is followed by a stage in which the dog seems to return to normal, except for persistent conjunctivitis. Next comes the clinical phase, during which occur most of the symptoms typical of canine distemper. The temperature remains high (about 39.5°C), the mucous membranes are inflamed, a discharge appears from the nose and eyes, the dog has diarrhea, and coughing reveals the presence of tracheobronchitis. The virus may be localized in various places: rhinitis, conjunctivitis, bronchial pneumonia (revealed by coughing and respiratory problems), gastroenteritis (causing diarrhea and vomiting), and keratitis (inflammation of the cornea) with ulceration are symptoms of complications due to the presence of bacteria. Later on, two types of nervous symptoms caused by the immune system's reaction to the disease may appear.

If the symptoms appear rapidly, paralysis, convulsions, involuntary muscle contractions, and coordination problems while walking may be observed. When the symptoms take longer to appear-up to several months-the dog will still have difficulty coordinating its movements, and this ataxia progressively becomes paralysis.

Involuntary muscle contractions and vision problems also occur.

There are several courses the disease can take. The dog may recover completely, without going through the clinical phase; or it may recover incompletely and suffer nervous, respiratory, or dental after-effects. Atypical forms of the disease also exist. There is a form that affects the skin and nerves, which causes a thickening of the nose and footpads, discharge from the nose and eyes, and persistent fever. This form progresses slowly. After a few weeks, encephalitis appears and leads to death. Another form of encephalitis (old-dog encephalitis) can affect old dogs, as the name implies.                  

At least four of the following six criteria must be met for a positive diagnosis of distemper: discharge from the nose and eyes, digestive symptoms, respiratory symptoms, nerve symptoms, and persistent fever, observed in a young dog. Laboratory tests will confirm the clinical diagnosis.

The disease is transmitted by direct contact between an infected animal and a healthy one. The virus is usually inhaled, and all body secretions contain virus particles. Treatments include a specific treatment, consisting of administration of high doses of serum, and a more general treatment allowing the dog to fight secondary infections, as well as the digestive and respiratory symptoms. Preventive measures are the most effective way to protect a dog against this disease. In large populations of dogs, it is preferable to quarantine animals being brought in. The facilities should also be disinfected. Vaccines exist, and can be used after the age of eight weeks. Dogs should be immunized as soon as possible.