Canine Distemper - Treatment

Treatment

Until recently, canine distemper has been associated with a long history of pessimism with respect to treatment of infected animals and the disease was usually assumed to have a poor prognosis. Most care offered was only palliative, geared toward easing the suffering. Several factors had an important role in maintaining the status quo.

Research and funding, for the most part, have focused on vaccination rather than on finding a cure for distemper.

In an outdated theory, the injuries that occurred were the result of a strictly autoimmune reaction, with the thought being that initially the canine distemper virus was introduced, but then subsequently eliminated, and that the cytokines continued to attack and damage healthy tissue in the absence of a current pathogen. Based on that theory, anti-inflammatory and immunosuppressive drugs have been prescribed by some veterinarians in an attempt to bring the effects of the condition under control, but this did not succeed.

It was later considered that the action of macrophages on infected nerve cells indicated the autoimmune reaction was likely a direct consequence of the presence of the virus. Often, owners seek expert help only when the disease is in its advanced stages (nervous phase) due to the nonspecific earlier signs and prescription of anti-inflammatory drugs (which are usually corticosteroids) undermine the immune system of the animal, allow the proliferation of the virus, and the autoimmune reaction increases as a means of containment of infected cells.

The first references to suggest effective treatments for similar viruses could be effective for canine distemper arose when studies found canine distemper was a disease comparable to measles, and infected animals could be used to develop new technologies for treatment of measles. The question of whether the reciprocal would be true was resolved when studies assessed the efficacy of traditional treatments for measles, some of which were successfully applied to animals with distemper.

Vitamin A and ribavirin as a treatment of distemper (and measles) are under evaluation and the modes of action remain unexplained. Some experiments suggest vitamin A and ribavirin could be effective as a treatment, but to date is not commonly employed in practice. Some evidence points to an indirect action, such as confirming a reduction in the amounts of vitamin A during infection, pointing to the hypothesis that it is raw material for some mechanism of resistance to infection. That the anti-infective characteristic is not specific to vitamin A is a mystery; however, there was no doubt about its effectiveness in this particular experiment, action mechanisms elucidated or not.

The adoption of ribavirin as a possible treatment for canine distemper followed the same steps as vitamin A; it was the principle used in cases of subacute sclerosing panencephalitis under measles. The first verification of the effectiveness occurred in vitro. The distemper virus was observed to be very susceptible to ribavirin, and 0.02 to 0.05 micromols are needed to induce its mechanism of error catastrophe and the inhibitory effect on virus replication by 50%.

The main concern in the use of ribavirin was the result of its interaction with the blood–brain barrier. As the brain is an immunologically privileged area, the concern was the capacity of ribavirin to overcome this barrier. In a study using mice with encephalitis due to measles, once the virus has become established in the nervous phase, the blood–brain barrier fails, in a way, reducing the restriction to the action of the ribavirin in these areas. The verification of all these results in vivo resulted in an effectiveness of 80% in animals that had already reached the nervous phase of viral infection. The application of ribavirin demands a close monitoring of the animal due the risk of leukopenia; also, the ingestion of long-chain tryglicerides (fats) are needed to better absorb the drug, and for preservation of gastric tissues, which are quite susceptible to it.

The medical and veterinary communities widely accept, while possible treatments are still being explored into their efficacy, prevention using vaccination is the most reliable way of preventing disease spread among the population.