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 specific injections, the problem is not yet over. The microfilariae (immature stages of the heartworm) are still circulating in the blood. The drug of choice may not have destroyed them all.
This, in itself, is interesting. The drug kills the adults, but may not kill the young immature worm, and the destruction of the microfilariae is critical to eradicating heartworm infestation. Having killed heartworms in the heart chambers, we should wait 7-10 days, not only for the disintegration of the worms to set in, but also to see if the dead worms would exude toxins that could further weaken the dog, which has already been debilitated by the insidious course of the disease and by the bombardment of the worm killing medication. Of course, supportive therapy (improved diet, supplementary vitamins, etc.) would have begun even before the treatment, and continued after the conclusion of the therapeutic interventions.
During those 7-10 days, the dog should be monitored for complications in the functioning of the lungs, liver, kidney, etc. If everything is relatively stable, we can continue to institute the chemical attack on the microfilariae with the same drug that kills the adult heartworms. We do that with the oral or injectable dosage of the 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. I should also mention that two scientists, William Campbell and Satoshi Omura, shared the Nobel Prize for Medicine in 2015 for their work in discovering Ivermectin, to combat roundworm-related infections and reduce the incidence of river blindness (a devasting disease in certain countries in Sub-Saharan Africa), lymphatic filariasis, as well as other ailments. The drug treats approximately 25 million people annually, preventing new cases of river blindness. It also prevents roundworms in billions of livestock and pets around the world.
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 unhesitatingly. It is a powerful drug. However, because the heartworms are so dangerous and endemic in the region, vets do not think twice to use the Ivermectin, even if the blood examination does not show the presence of microfilariae.
Remember, however, the point (and the reasons therefor) I made previously: a negative result does not mean that there are no organisms in the blood.
After the second treatment with the microfilaricide (to kill the immature heartworm stages), the blood should be monitored regularly for at least another two weeks, and often in the ensuing years, during which time the animal should be placed on a prophylactic regime of a routine administration of the microfilaricide.
Given that Guyana has ideal climate for the spread of heartworm disease, there are several species of mosquitoes that spread the microfilaria, and we continue to be plagued by the presence of strayed dogs (un-spayed females of particular concern), it is incumbent on caregivers to have their dogs checked, treated (if positive), and placed on the routine prophylactic regime. If not, I fear that the disease will reach alarming rates in the future.
Next week we shall deal with the control aspect of this disease.
