Microfilaria are the offspring of adult heartworms. They are produced in massive numbers in canines infected with Dirofilaria immitis (the taxonomic name for the heartworm parasite).
In some ways microfilaria can be worse than the adult canine heartworm. When large numbers of them die suddenly they can cause a shock reaction and death. That is why you should never give heartworm preventive to a pet who has missed a dose or who might have heartworms.
Microfilaria can cause reactions that affect veins and arteries in the body, make deposits in kidneys and even cause eye and brain damage.
There are almost as many protocols for treating heartworms as there are doctors of veterinary medicine. The system we follow calls for microfilaria to die at the beginning of the heartworm treatment, which is why Elvis is in the hospital with us today.
We have administered an oral medication to kill the offspring, and will monitor Elvis every ten minutes throughout the day, so that if he has any reactions to the dying microfilaria we can quickly inject medication to reverse the reaction.
Elvis is one of those dogs who had a negative heartworm test six months ago, but, having been a stray, had not been on a heartworm preventive prior to his negative test. So, we were not unduly surprised when his six-months-later test came up positive.
Thanks to youth, good pre-treatment laboratory test results (CBC, Chemistry Profile and Urinalysis) and a chest radiograph with minimal heartworm-related changes, Elvis should come through the treatment with few or no difficulties.
See you tomorrow, Dr. Randolph.