Pets and People: Distemper in Dogs



The basic vaccine for dogs against Distemper is commonly referred to as “the distemper shot,” though it also covers several infections besides distemper.  First-hand experience with this disease has become limited because of widespread vaccination.  The typical distemper suspect is a rescue or pet store dog or puppy, usually with questionable vaccination history or an as yet incomplete vaccination series.  

The dog or puppy that has been housed with other rescue dogs or with a group of dogs/puppies that have been shipped together.  Symptoms begin with Gooey eyes and nose discharge, fever, which often comes and goes unnoticed, poor appetite and coughing and development of pneumonia.

The attacking virus interfaces with the body’s mucous membranes and starts with the respiratory tract, causing a pneumonia, but it does not stop there.  The virus moves on to produce vomiting and diarrhea, callusing of the nose and foot pads.  Thus, one of the old names for distemper was "hard pad disease."

After completing what is called the mucosal phase of infection where environmental interfaces are attacked, the virus proceeds to the central nervous system for its neurologic phase leading to seizures, classically starting with snapping or tremors of the jaws that progress to convulsions of the whole body.  This distemper classic sign is called a "chewing gum fit”. Seizures are not the only distemper sign.  Tremors, twitching, imbalance, and limb weakness all may occur.  Signs may progress to death or may become non-progressive and permanent.  Recovery is also possible.

This means that the dog appears to recover only to break with neurologic disease one to three weeks later.  Younger puppies or individuals with weak immunity often die during the mucosal phase while stronger individuals may have relatively mild mucosal signs and not appear ill until the neurologic phase strikes.

The virus is shed in most body secretions, including urine, the infected dog typically spreads the disease through coughing infected secretions that get inhaled by the new host.  The virus enters the new host via the nose or mouth and promptly begins to replicate.  The 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; instead, the virus is able 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 sixth day, the virus has migrated to the spleen, stomach, small intestine, and liver.  Fever is developing at this point.

By day eight or nine, an important hurdle 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 that 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.

Most cases involve 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 immunity 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 dogs of all ages.

Diagnosis of distemper has traditionally been based on the constellation of symptoms, and for decades there was no reliable test for the infection. PCR technology has changed this as it is now possible to test for viral DNA and to distinguish infection from exposure to the virus from vaccination.

Many protocols have emerged over time as we grope for meaningful anti-viral therapy.  The fact remains that recovery from distemper is all about immunity and the only real treatment is supportive care while the patient mounts an immune response. If the patient has pneumonia, antibiotics are used on the secondary bacterial infections.  Airway dilators are used as needed.  Physical therapy is used to promote coughing.  If the patient has diarrhea, intravenous fluids are used to prevent dehydration.

Prior to widespread vaccination, distemper was the scourge of the canine community, wiping out entire towns of pet dogs.

Today, distemper is a rare disease except in the shelter, rescue, and pet store world.  The “distemper shot” is the basic immunization for dogs.  It is generally combined with vaccine for canine parvovirus as well for parainfluenza, adenovirus 2, leptospirosis, and sometimes coronavirus.

Puppies are vaccinated beginning at age 6-8 weeks and then every two to four weeks thereafter until age 16 weeks.  The next vaccine is one year later.  After that subsequent vaccination boosters are given every one to three years or based on antibody levels depending on the policy of the supervising animal hospital.

Classically, the neurologic phase of distemper occurs one to three weeks after the mucosal phase resolves but can potentially occur months afterwards.  Sometimes the mucosal phase is so minor that it is not noticed, as might occur in a dog that is older or has received some vaccines but not enough for full protection.  For these dogs, the neurologic phase seems to come out of nowhere.  Often a dog can survive even a severe mucosal phase, but the development of a neurologic phase is a more serious blow to the dog's ability to recover.

The owner of a distemper suspect will have numerous questions.

The distemper virus attacks epithelial cells.  These are cells that line the interfaces with the environment, including the mouth.  In puppyhood the buds of the permanent teeth are still developing from epithelial cells.  The distemper infection and associated fevers can leave these tooth buds permanently damaged so that the adult teeth come in with stained and pitted enamel.  This is called enamel hypoplasia.

One of the few positive aspects of distemper is that the virus cannot live without fresh secretions; it is inactivated in minutes to hours outside the living host’s body.  Minimal disinfection is necessary.

A recovered dog may shed virus up to two to three months. It is important to keep this in mind when taking a recovered pet anywhere where there are other dogs.  The most intense viral shedding occurs in the first two weeks of infection.

Humans can get infected with the virus, meaning the virus seems able to replicate in the human body, but no illness results.  At one time, multiple sclerosis was thought to be associated with exposure to the canine distemper virus, but further research suggests that it is actually the human measles virus (a close relative of canine distemper) that may be the culprit.  It does not appear that there is any human hazard in the canine distemper virus.

After an infection, the vaccine is not required, however, the "distemper vaccine" is actually a combination vaccine covering up to seven infections, including canine parvovirus. You may not want to skip these other important vaccinations.  Further, confirmation of distemper infection can be problematic.  This raises the question as to whether there is any harm to vaccinating with a product that includes a possibly unnecessary distemper vaccine.

In fact, if a dog has recovered from distemper, there will be a rapid antibody response against the distemper vaccine live virus, and it will be inactivated just as a natural infection would be.  While a recovered dog does not need distemper vaccination, there is no harm in continuing to give the vaccine and reaping the benefit of the additional infections typically covered in the product.


dog breeds, distemper, vaccination, infection, canine distemper, fever, immunization, human measles virus, anti-viral therapy