Well, let’s see what we have learned about this rapidly spreading scourge of Heartworm in dogs.
Firstly, we know that it is transmitted by mosquitoes.
Secondly, we know that the adult worms (bundles of them) live in the right heart chambers (and sometimes in some of the big and important blood vessels), thus greatly compromising the function of the heart and the transmission from the heart to the organs.
Thirdly, and very importantly, we know that this disease (i.e., the development of the visible symptoms) sneaks up on the poor animal, and by the time we begin to see signs of the ailment, the efficiency of many organ systems (liver, kidney, lungs, the heart itself) is impaired.
Lastly, we had documented that the main symptoms were (i) a soft, deep cough, (ii) lethargy, (iii) loss of condition (weight loss), and (iv) sometimes a swelling of the limbs (especially the hind legs).

Here are answers to some of the most
frequently asked questions on Heartworm disease
Q: How do we keep tabs on the possibility of this disease
A: Simple. We check the blood regularly. Your veterinarian can take a droplet of blood and examine it under the microscope. Once the microfilariae (the immature stages of the Heartworm) are seen, that is indicative of the presence of adult Heartworms in the right heart chambers, and possibly in large blood vessels as they leave the heart.
Q:Is the Heartworm test reliable?
A: You will recall that, in my last column, I said this laboratory diagnosis is not straightforward. Not discerning the immature stages of the Heartworm in the blood sample does not mean that there is no Heartworm. This is because:
(i) Some of our veterinarians administer a broad spectrum dewormer which contains exactly the same drug that kills the microfilariae (immature stages of the Heartworm)! This means that if this very efficient drug kills the microfilariae and adult Heartworms, then the vet might not find them when the blood sample is observed under microscope. Yet, some adults could be still existing in the heart quite happily, thank you.
(ii) The number of microfilariae that are circulating at the time the sample is taken might be very small, and they will not be easily picked up during the microscopic examination of the blood droplet.
(iii) Some dogs actually have such a strong immune system that it develops antibodies (defences) that can kill many of the microfilariae which end up in the blood stream.
(iv) At the time when the blood sample was taken, the worms in the heart might not have reached the stage of actual sexual maturity. In other words, they were not quite adult, and therefore could not have mated and produced the microfilariae.
(v) Lastly, and remotely possible, the worms in the heart could be of one sex only (all males or all females). Consequently, they would be unable to mate and reproduce offspring (microfilariae).
Q: What does all of this demand of your veterinarian?
A: Simply put, your veterinarian must make it a part of his or her routine examination to check the dog’s blood for this parasite. This means (which can be deduced from the points made above) that the samples must be taken at regular intervals. It also means that if, after several blood checks, there is no sign of the microfilariae, then and only then should prophylactic measures (medication) be administered. If, on the other hand, the presence of a Heartworm burden has been identified, therapy must immediately be introduced, or the dog will die a slow and excruciating death (guaranteed!).
The prevention and cure of Heartworm Disease will be dealt with next week.