Destruction of the immature stages
Last week we concluded the article by saying that even after the adult heartworms in the right heart chambers (and elsewhere) have been killed by the series of arsenic injections, the problem is not over. The microfilariae (immature stages of the heartworm) are still circulating in the blood. The arsenic did not destroy them as well.
This, in itself, is interesting. Arsenic kills the adults but not the young. I can’t explain this. Perhaps I missed this day in school. What am I talking about? When I went to school, canine heartworm seemed not to be a problem. Did it exist as a killer malady? No textbook of my generation refers to heartworm. So where did the canine heartworm ailment suddenly arrive from? And that’s not the only such disease. The canine parvovirus disease (we’ll deal with this killer in detail at some later date) is another ailment that we did not cover in vet school.
Today, canine parvovirus is a big-time infection and receives immense coverage during the course of a vet’s education. Yet none of the texts tell us how these diseases suddenly have emerged over the last 20 years as big time problems.
One might argue that canine parvovirus was always there, but now new laboratory techniques allow us to recognize it. I don’t buy that. Even 20 years ago, lab facilities were good enough to detect parvoviruses.
Perhaps one can argue that the virus has evolved from a relatively innocuous, non-lethal blob of protein into the killer it is today.
Well, that is at least a more acceptable theory. But it does not explain the current ubiquitous presence of heartworm and its ability to kill a large percentage of dogs.
Twenty, thirty years ago we were not blind.
Surely, we would have seen (during post mortems) the spaghetti-like bundles in the heart if the disease existed and had a great incidence. But we didn’t.
I don’t have the answers, but the questions are interesting. Of course, if any of the readers know the answers, or have scientist friends/family abroad or locally who might know the answers, please educate us.
On the whole, you know, these columns should represent a two-way stream of information sharing.
Anyway, let’s get back to the destruction of the larvae. Well, now that the heartworms in the heart chambers are dead, we should wait 7-20 days not only for the disintegration of the worms to set in, but also to see if the dead worms will exude toxins that could further weaken the dog that has already been debilitated by the insidious course of the disease, and by the bombardment of arsenic injections as the drug/cure of choice.
Of course, supportive therapy (improved diet, supplementary vitamins, etc) would have begun even before the arsenic treatment, and continued after the conclusion of the therapy.
During those 7-20 days, the dog should be monitored for complications in the functioning of the lungs, liver, kidney, etc. If everything is relatively stable, we can begin to institute the chemical attack on the microfilariae.
We do that with the oral or injectable dosages of a drug called Ivermectin. This drug is one of the major achievements in the constant quest to improve the artillery which is used to combat pet/livestock diseases.
This drug claims to kill both ecto-parasites (ticks, fleas, lice, mites) and endo-parasites (intestinal worms)! We know it kills the microfilariae and we administer it because it works. But it is a rough drug. Yet, because the heartworm is such a dreaded disease, I don’t think twice to use the Ivemectin even a second time, a week later, even if the blood examination does not show the presence of microfilariae (which should mean that they are all dead).
Remember, however, the point (and the reasons therefor) I made previously: a negative result does not mean, 100 per cent, that there are no larval stages in the animal’s body (perhaps they are hiding in the lymph or in the fluids surrounding the brain or in joints).
After that second treatment with the microfilaricide, the blood is monitored for at least another two weeks.
The animal should then be placed on a prophylactic regime of a routine administration of a microfilaricide.
Next week we’ll deal with the control aspect of this disease.
Please implement disease preventative measures (vaccinations, routine dewormings, monthly anti-heartworm medication, etc) and adopt-a-pet from the GSPCA’s Animal Clinic and Shelter at Robb Street and Orange Walk, if you have the wherewithal to care well for the animals. Do not stray your unwanted pets, take them to the GSPCA Clinic and Shelter instead. If you see anyone being cruel to an animal, get in touch with the Clinic and Shelter by calling 226-4237.
