Mosquitoes play an essential role in the life cycle of a 10-12 inch worm which is extremely common in this climate zone, yet almost never seen by human eyes. That’s because the heartworm conducts all of its business inside, in the dark, in secret. It lives inside the large vessels that are attached to the heart, in communities of a dozen up to a couple hundred individuals. That’s right, a couple of hundred. Submerged in blood, their presence is easily overlooked while the host gradually becomes more and more debilitated. During that time, the worms are happily mating with each other and producing hordes of microscopic offspring small enough to fit easily through the bite mark of a mosquito. Once they’re sucked into their flying transport during the next mosquito attack, they spend a couple of weeks on board gathering up the energy to get a place of their own. Then they disembark, entering a new animal through a fresh mosquito bite. They burrow around under the skin here for a while, until they’re ready to dig their way to the heart. This moment is the only time when heartworms can be removed from an infected pet without endangering his safety. Once they move away from the skin and reach maturity, the risk involved in treating this condition escalates sharply.
Adult heartworms live near the large pulmonic heart valve, where their crowded, bundled bodies obstruct blood flow and cause substantial inflammation. That’s all happening inside the blood vessels, 24 hours a day—you know, the place where you object to the presence of a tiny, sterile needle for 30 seconds during your annual physician visit. Their lifespan is several years, entirely spent wriggling around (as seen on cardiac ultrasound) and replicating themselves. Eventually they die of old age, but even in death they wreak havoc. A floating heartworm corpse can cause even more damage as it moves downstream and forms a cork in one of the smaller vessels.
Heartworm is a devastating parasite that’s very common in many regions of the world. Even though this thing is the size of a spaghetti noodle and goes everywhere your dog does, accompanied by 100 of its closest friends (the kind with benefits, am I right?), you will never, ever lay eyes on it. A less attentive person than yourself might forget that they even exist. And that could lead to some very serious consequences.
Dr. M.S. Regan