Almost everyone has heard of distemper, and most dog owners know that their pet needs some type of ‘shot’ in order to protect them against this disease, but that may be the total extent of their knowledge.
As we discuss his temper in this article series, please keep in mind that the discussion will be generalized and based primarily on research findings. Averages are the basis for any vaccination recommendations and in no way reflect individual variations, individual problems, geographical peculiarities, practitioner preferences, etc.
Every program for vaccinating animals against distemper is based on compromises according to the prevalence of disease, owner convenience, cost, and many other factors. In the final analysis, the pet owner must trust his veterinarian to provide adequate protection.
The Disease
Canine Distemper (CD) or Carre’s Disease, is caused by a virus which attacks epithelial and nervous tissue cells. It can affect lymphoid tissue, the intestinal tract, nerves, the brain, lungs, footpads, and other epithelial tissue in the body. ‘Hard Pad Disease’ is nothing more than one of the many clinical manifestations of the distemper virus.
There is only one strain of canine distemper so the many clinical syndromes are only a reflection of individual response to the disease. The virus will infect dogs, fox, wolves, dingoes, coyotes, raccoons, weasels, ferrets, mink, and skunks.
Transmission of the CD virus is through discharges from the eyes, nose, or mouth of infected animals. These enter the respiratory system either by direct contact or with virus-laden dust or droplets. Flies can also mechanically transmit the virus. Urine and feces may also contain the organism and thus act as a source of infection.
At warmer temperatures, the virus appears to be very unstable outside of a host and may only survive up to a few hours. In fact, at temperatures of 140 degrees for 30 minutes will destroy the virus, as will many chemicals. In colder environments, however, the virus may lie dormant for long periods and reactivate with warmth.
This can be used as a guideline as to when a new dog can be brought into a home which has harbored a distemper case. In warmer weather, a few weeks should be more than sufficient, but in a cold climate, the backyard may act as a source of infection as the temperatures rise. Incubation is about one week. This is the time which takes for a virus to cause the disease from the time it enters the body.
The signs of distemper vary, but most often include thick, pus-laden discharges from the eyes and nose, along with a deep productive cough, vomiting and diarrhea, pustules on the abdomen, convulsions, body or leg spasms, loss of appetite, weakness, depression, high fever which may fluctuate to normal, and thickening of the footpads
Obviously, other conditions can cause the same signs, many of which are not as serious and much easier to treat. A problem in diagnosis always confronts the veterinarian in early cases of canine distemper or those not following a typical pattern since positive confirmation of the disease depends on the sophisticated procedures of virus isolation and fluorescent antibody technique. Most veterinarians diagnose and treat based on clinical experience.
There Is Still Plenty Of Research To Do
As with most viral diseases, there is no specific drug which will attack the CD virus in the body. Treatment is aimed at fighting secondary infection and controlling symptoms such as coughing, diarrhea, and convulsions. Vitamins and other bodybuilders are often used to ward off debilitation and assist the animal’s own ability to fight the disease. Drugs such as ether and vitamin C have been advocated as therapy, but their value is yet to be proven in critical studies.
Distemper antiserum and vaccine have likewise been used therapeutically, but studies have shown that dogs with signs of distemper already have formed their own antibodies to the disease.
It is interesting to note that animals raised under sterile conditions show only very mild signs when infected with canine distemper. Apparently secondary bacterial invaders are responsible for the severe forms seen in practice. The virus seems to break down body tissues and resistance allowing other organisms to do their damage. This would partially explain the many clinical variations encountered.
The survival rate for this disease is not very high, especially if the animal is showing nervous system involvement, such as seizures and muscle spasms. Many cases follow a prolonged course of treatment and care. In spite of vigorous therapy and good nursing care, many dogs still have to be euthanized because of the intense suffering. It should be obvious that prevention is the best solution to a disease of this severity.
How Vaccines Work
A description of the basics of immunity will help in understanding vaccination procedures used to prevent canine distemper. When a foreign substance enters the body (antigen), it reacts to destroy this invader.
One of the reactions is antibiotic formation. These are proteins that circulate in the blood, attach to the foreign substance, and form a harmless complex. It takes the body a few days to start making the antibody but once started, the antibody will persist for quite some time. Each different invader will stimulate the formation of the new antibody.
There are four types of vaccines for the prevention of distemper: Serum, Killed Vaccine, Modified Live Vaccine (MLV), and Measles Vaccine.
Serum
Not actually a vaccine, this is a portion of the blood taken from dogs with immunity to distemper. It does not stimulate an immune response and its longevity after injection is relatively short, about a few days. It is a rapid source of antibodies and the advantage is immediate protection. The disadvantage is its short duration and interference with the vaccine. It is not usually used in a vaccination program but rather in situations such as pet shops, pounds, etc., where immediate protection is necessary.
Killed Vaccine
This is produced by growing the distemper virus in the laboratory and then destroying it carefully. The end result is a virus particle which will not reproduce or cause disease, but still acts as an antigen and stimulates immunity (antibody production). The major disadvantage is that a fixed amount of virus particles is injected into the dog, which limits the intensity of the antibody response.
Modified Live Vaccine (MLV)
The process for producing this type of vaccine involves growing the virus in the laboratory under conditions that render it harmless but do not kill it. When this vaccine is injected, it has the ability to multiply in the body, but yet it will not cause disease. This provides a vast source of antigen and an abundance of antibody.
The duration and height of protection with this type of vaccine are excellent. It is presently the vaccine of choice for permanent distemper protection. Canine hepatitis and leptospirosis are often combined with MLV distemper vaccines. Care must be taken in the production and handling of this vaccine.
Measles Vaccine
The viruses which cause canine distemper, rinderpest of cattle, and human measles are all similar antigens. The measles virus, when injected into the dog, will stimulate antibody product which will protect the dog from distemper. The advantage of this drug is that distemper antibodies given to a young puppy through the female’s milk will not attack measles virus, whereas they will attack distemper vaccines.
The result is that very young pups (3 to 4 weeks old) can be vaccinated and develop some permanent immunity. There is still controversy among many authorities as to the value of the measles vaccine in a vaccination program.