Canine Distemper

Canine Distemper, and its chronic form Hardpad, has been one of the longest recognised diseases in the dog. Before the introduction earlier this century of the "Epivax" vaccine (®) by Burroughs Wellcome distemper caused more deaths and permanent disability in young dogs than any other infectious disease. Epivax is now superceded by the tremendously improved modern vaccines, but some of our senior clients will still surprise us by asking for their dogs to be 'Epivaxed'.

The Virus

Canine Distemper Virus (CDV) is a Paramyxovirus and belongs to the same group of viruses which includes the virus of Measles in man. Although dogs are the most commonly affected species, CDV is also seen in foxes, ferrets, mink and silver foxes. In the Downland Veterinary Group area we regularly see foxes, particularly cubs, with CDV infection, and this forms the nucleus for the continuation of exposure in our pet dogs.

At normal temperatures the virus is very stable and can stay active in infected material for several weeks, provided it does not dry out or is not exposed to ultraviolet light (ie sunlight). At below zero temperatures it can stay active for many months, but at temperatures above 32°C it is rapidly inactivated.

The virus is found in almost any secretion from an infected dog. It is passed out in vast numbers in saliva, urine and faeces. It is likely that the most route of infection between animals is the inhaling of virus in droplets produced by an affected dog's coughing in the near vicinity.

Like all viruses the CDV rapidly invades cells and uses the cell's reproductive mechanism to reproduce itself. Once in a cell the virus is protected and it is very difficult for the immune system to get at it to destroy it. Many thousands of new virus particles are released when the cell dies.

The Disease

The initial disease in dogs can appear quite mild, but the severity of the symptoms steadily increase dispite treatment until the dog is often destroyed on humane grounds. CDV infection can take a month to show all of its worst characteristics, and things can still deteriorate from then on.

Having contacted the virus, the dog will appear clinically normal for about four days. It will then start to show the initial signs of infection with watery eyes, runny nose and a sore throat. The dog runs a temperature of 103.5°F (39.7°C) which will not respond to any routine treatments to reduce it. Over the next day or so the discharges rapidly become purrulent, the tonsils become very enlarged, and the dog often also gets diarrhoea and pneumonia as a direct result of invasion by the virus.

The picture or a depressed puppy with matted eyes, caked nose and gulping as it tries to swallow liquid food is one which is heart rending, particularly when one knows that treatment is only trying to alleviate the symptoms as much as possible, and that one can only hope for the immune system to be able to overcome the infection. Antibiotics cannot destroy CDV. (see Immunity and Disease)

The dog will steadily lose weight and condition, and need constant nursing to try to reduce the effects of the infection.

Just as it seems that we may be winning however, distemper throws in its next stumbling block. The distemper virus affects the brain. After about four weeks of treatment the dog starts to show signs of regular twitches, often of a facial muscle or in a leg. These twitches worsen, until the dog starts to show full blown fits and convulses violently. The poor debilitated dog is groosly weakened by the strains on its already depleted reserves, and as the convulsions increase in frequency euthanasia is usually carried out at this stage if not necessary before. If left the fits will increase so that the gaps between individual attacks are only due to exhaustion and the dog will die horribly from the effects.

With excellent clinical care and nursing a dog may recover to be able to lead an acceptable life. If the immune system can eventually over-ride the CDV then the dog can recover its condition and eliminate the virus. During this recovery the dog is still passing out billions of virus particles into its surroundings for some months and is still a danger to any other dog with which it comes into contact. It will also in the majority of cases be left with at least a permanent twich if not intermittent convulsions as a result of permanent damage done to the brain while the virus was active. Many dogs will need constant anti-convulsant medication for life.

Diagnosis

Diagnosis is made in the majority of cases on the clinical history. The presence of the prime symptoms, an increased temperature which will not respond to treatment and with a history of no vaccination, or lapsed vaccination is often diagnosis enough.

Blood samples taken at intervals from affected dogs will also show increases in the levels of antibody present against CDV. However this rise is often found too late for the prevention of permanent damage, particularly to the brain.

Blood samples can also be examined by specialised laboratories who use Immunoflourescent techniques to show the presence of virus in the white blood cells. This is usually at about 2-3 weeks post infection, and again rather late on to prevent damage being done.

Of course these are plenty of tissue samples available to confirm the presence of CDV at post mortem examination, but that is a little too late to help!

Treatment

There is no effective specific treatment for Canine Distemper

The vast majority of dogs with this disease have to be humanely destroyed.

The only treatment which we can use to try to help these wretched dogs is to support them as best as we can to reduce the debility which occurs as a result of the disease, and hope that the dog's body can respond.

Antibiotics are used to try to control secondary bacterial infections which can come as opportunists on top of the debility caused by the CDV. Palliative drugs are used to help control the diarrhoea, help breathing, ease the throat discomfort etc. and intravenous drips are used if necessary to replace body fluids and supply nutrition where possible.

There is a hyperimmune serum available which can be injected into the vein to give high levels of antibody to affected animals. It is expensive and has little if any effect once the symptoms of the disease have become evident. It is sometimes of use to try to protect dogs at risk who are in contact with an infected dog.

The major treatment is extensive nursing care. Continually cleaning the eyes, and unblocking the nostrils, cleaning the diarrhoea and stopping 'nappy rash' and pressure sores from developing are essential if the dog is to obtain any relief.

In the later stages the use of anti-convulsant drugs may help to control fits and spasms. These have varied success. It does seem likely however that if treatment with anti-convulsants begins as soon as a diagnosis of CDV infection is made, then the fits and spasms may well not be so severe.

Treatment will need to continue for a minimum of eight weeks in the majority of cases and some teeatment may be needed for life.

Hardpad

One of the manifestations of CDV infection which is seen in some outbreaks is a situation where the general symptoms are much milder than may be expected. With these cases the damage seems to be caused by the virus affecting the growth layers of the thickened skin of the nose and the pads of the feet.

The pads and the nose leather produce an excess of hard skin tissue This is thicker than the normal tissue and dries and cracks, making the pads bleed and and be very sore. This tends to become a liflong problem.

Vaccination

Vaccination with a
good quality licensed vaccine
is the only sensible way to give a dog protection against Canine Distemper

It should be evident from all that has been described above, that CDV infection is a horrendous disease, with a very poor chance of success even with the best treatment. The only way to avoid these horrors is the provision of high antibody levels in the bloodstream which can eliminate the virus before it enters the cells of the body and begins to do damage.

Modern vaccines are very safe and very effective (see Vaccines and Safety). It is very rare for a dog not to respond to a vaccine although failures do occur. Circulating antibodies are built up to high levels over the ten to fourteen days after vaccination and are maintained at protective levels for about two years.

Routine vaccination initial courses can begin from six weeks of age. Completion of the initial course can be at 10 weeks of age, and the puppy can safely go out into the big wide world two weeks later. Note that some vaccines are not effective if the course is completed before twelve weeks of age, so that the puppy is a further two weeks older before it can go out and mix with other dogs.

At one time, when fewer dogs were vaccinated and there were many affected dogs in the neighbourhood, vaccination gave the initial protection as the maternal immunity waned, and whenever the dog went out it met CDV in the environment and gave its immune system a natural boost. Nowadays the majority of dogs are vaccinated and this natural stimulus has been largely lost. It is now recommended that dogs are revaccinated against distemper every two years to ensure that the amount of antibody stays at a high enough level to maintain full protection.

Distemper vaccination in the dog is now usually combined with other vaccines in a single dose. We routinely aim to protect against seven different diseases including distemper with a single dose.

At Downland Veterinary Group we use the Nobivac (® Intervet UK Ltd) range of vaccines. This range is recognised as being one of the market leaders for safety and efficacy. We could use a cheaper vaccine, but we couldn't use a better vaccine!