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 microfilaria (immature stages of the heartworm) are still circulating in the blood. The arsenic did not destroy them as it did the adults.

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 school there was no heartworm problem. No textbook of my generation refers to heartworm. So, whence did they suddenly arrive? And that’s not the only one. The Canine Parvovirus Disease (we’ll deal with this killer in detail at some later date) is another ailment that was not covered in veterinary school five decades ago.

Today, Canine Parvovirus Disease (CPvD) is a big time infection and receives immense coverage during the course of a veterinarian’s education. It is interesting how this disease and quite a few others have emerged over the last fifty (even 20-30 years) years. Mad Cow Disease and Swine Flu fall into this category.

One might argue that Parvovirus was always there, but now new laboratory techniques allow us to recognize it. I don’t buy that. Even 50 years ago, lab facilities were good enough to detect Parvoviruses. We knew that these especially tiny (“parvus” is the word for “small” in Latin) viruses existed; but CPvD was not an issue. One can offer the explanation that the virus has evolved from a relatively innocuous, non-lethal blob of protein into the killer it is today. Also, environmental conditions might have changed in such a way as to nurture and ensure the pathogenicity of the organisms.

This curious female dog is looking for a home. She has been spayed.

But does all of this theorizing explain heartworm? Twenty to thirty years ago we were not blind. Surely, we would have seen (during post-mortem examinations) the spaghetti-like bundles of worms in the heart, if the disease existed in any great way.

I don’t have the answers, but the questions sure are interesting. Of course, if any of the readers have explanations to these conundrums, or have scientist friends/family who might know the answers or possess better explanations, please share them with us. On the whole, you know, these columns should represent a two-way stream of information sharing. Many thanks to those who do take the time to write us.

Anyway, let’s get back to the destruction of the young, immature heartworms (circulating in the dog’s blood stream) after we have killed the adults. Once the heartworms in the heart chambers are dead, we should wait 7 to 10 days not only for the disintegration of the worms to set in, but also to see if the dead and dying adult worms will exude enough toxins (poisonous chemicals) that could further weaken the dog that has already been debilitated by the insidious course of the disease, and by the bombardment of the arsenic therapy.

In fact, there are many valid arguments to support the practice of killing the immature stages (microfilaria) of heartworms, before we proceed to destroy the adults. The problem is that the arsenic treatment is so expensive that it is more practical to keep killing the immature stages and let the adults in the heart chambers die of “old age”.

Of course, supportive therapy (improved diet, supplementary vitamins, etc) would have begun even before the arsenic treatment; and it must be continued after the conclusion of the therapy.

During those 7 to 10 days, the dog should be monitored for complications in the functioning of the lungs, liver, kidneys, etc. If everything is relatively stable, we can begin to institute the chemical attack on the microfilaria (immature stages of the heartworm).

We do that with the oral or injectable dosage of a drug which, to my mind, is one of the major achievements in the constant quest to improve the artillery used to combat pet/livestock diseases.

This drug claims to kill both ectoparasites (ticks, fleas, lice, mites) and endoparasites (intestinal worms). We know it kills the microfilaria, once we see the immature worms in the blood droplet under the microscope and vets should administer the drug without hesitation. But it is a rough drug. Yet, because the heartworm is such a dreaded disease, I don’t think twice to use the Ivermectin (the name of the drug) even a second time, a week later, even if the blood examination does not show the presence of microfilaria (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 more immature heartworms in the blood.


After the second treatment with the microfilaria-killing drug the blood is monitored for at least another two weeks. The animal should then be placed on a prophylactic (prevention) regime of a routine (monthly) administration of the Ivermectin or any other of the other heartworm prophylactic drugs (DEC salt is one such chemical; you would have to use it daily in the dog’s food, just as it is recommended in humans – after all, the filarial worm that causes Canine Heartworm Disease is very similar to the organism that causes “big foot” in humans).

NB: All of the above becomes unnecessary, if we begin a monthly anti-heartworm treatment when the dog is 6 months of age.

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’s Clinic and Shelter instead. If you do not wish your pet to have puppies or kittens, you may exploit the GSPCA’s free spay and neutering programme. If you see anyone being cruel to an animal, or if you need any technical information, please get in touch with the Clinic and Shelter by calling 226-4237.