The incidence of distemper steadily declined to such an extent that many veterinary graduates in urban areas often were in practice for some time before a case of distemper came their way.
In human and veterinary medicine, when a disease has been efficiently controlled with a simple vaccination procedure, there is a tendency to become complacent and neglect the very procedures that brought about a diminution in the incidence of the disease. This has happened with canine distemper.
Veterinary practitioners in the U.S. have reported seeing a higher than usual number of cases of distemper. In most cases the dogs involved had not been vaccinated, but in the case of some greyhounds they had received at least one vaccination.
Distemper in dogs is caused by a virus infection. The earliest signs of the disease is usually of yellowish discharge from the eyes and nose, accompanied by a mild fever. The owner often ignores these early signs as he thinks the dog merely has a cold.
As the virus proliferates in the dog’s body, it may attack the respiratory system causing tonsillitis and coughing and eventually pneumonia.
If it attacks the digestive system, vomiting and diarrhea occur, but the worst feature of the distemper virus is that it frequently attacks the nervous system producing a variety of serious symptoms.
The dog first develops localized nervous spasms affecting the muscles of the head or limbs. These gradually become more severe, producing violent fits and paralysis.
As the cause of distemper is a virus, antibiotics are useful in controlling only the effects of the secondary bacteria infection. Once nervous symptoms become apparent the chances of recovery are very poor. Some dogs seem to recover from the initial respiratory or enteric forms of the disease only to develop nervous symptoms two or three weeks later.
Vaccination is the only method of preventing canine distemper.
The newer form of vaccine is produced from live, non-virulent virus grown in tissue cultures.
Such pure standardized vaccine eliminates the problems that were experienced with older type vaccines, which occasionally included virulent infections or produced ill-effects due to the animal becoming hypersensitive to some of the impurities.
It is recommended that puppies be given the first distemper vaccination at 6 weeks of age. A second vaccination is then necessary at 12 to 14 weeks, then again a year later. Subsequent vaccination is then advised every 1 or 2 years, depending on the preferences of the individual veterinarian.
Breakdowns in immunity from vaccination are now fortunately rare. Where they have occurred they have usually been traced to the animal not receiving vaccinations after the initial puppy vaccination.
The immunity gained from a single vaccination before 12 weeks can be affected by the presence of immune factors derived from the mother. These can be present up to 12 weeks of age, hence the recommendation to vaccinate again after 12 weeks.
Dogs kept either in their own backyards or on rural properties do not have the opportunity to have their immunity challenged and subsequently reinforced by contact with other dogs carrying the natural disease. It is therefore most important to regularly re-vaccinate animals in isolated situations.
It has been suspected that the presence of the virus which causes canine parvovirus disease may inhibit the ability of an animal to produce an adequate immunity from a vaccination against distemper.
This effect of the parvovirus is termed “immunosuppressive”, and accounts for the fact that the normal defense mechanisms of the dog are almost completely absent after infection with the natural parvovirus disease.
This does not mean that dogs should not be vaccinated with distemper and parvovirus vaccine simultaneously. The killed parvovirus vaccine does not inhibit the normal dog’s ability to produce a good immunity from both vaccines.
The presence of the virulent parvovirus in boarding establishments or breeding kennels could explain why there is an apparent breakdown of the immunity in previously vaccinated dogs introduced into such an environment, or why some vaccinations performed in such places fail to produce a satisfactory immune response.