Heartworm disease is a serious illness in dogs and cats caused by a parasite called Dirofilaria immitis. It spreads through mosquito bites and is found in many parts of the world, including North Carolina. If you’ve been to our hospital you’ve heard us stress that if left untreated, heartworms can be deadly. We are all a part of the battle against heartworms, and now that a drug-resistant strain is spreading in parts of the U.S., it’s more important than ever to make sure your pet’s prevention plan is truly effective.
The Weapons. To prevent heartworm, veterinarians use a group of medications called macrocyclic lactones. These include drugs like ivermectin, selamectin, and moxidectin. But not all of these medications are created equal and provide protection against resistant strains.
The Resistance. Since 2005, there have been reports that these medications don’t always work. By 2015, research confirmed what we already suspected; some heartworms had developed resistance to these drugs. This means the parasites can survive even when treated, making prevention more difficult.
The Battle. The data is confusing, though. Heartworm infection in a pet receiving medication doesn’t always mean that the parasite is drug-resistant. Sometimes, the problem is missed doses or incorrect use. Testing for true resistance is complicated, expensive, and raises ethical concerns. Scientists still don’t fully understand the genetic changes behind resistance.
The Strategy. But we do know that the most effective weapon against heartworm disease is a monthly preventative. But dosing matters a lot when it comes to preventing heartworm resistance. Subtherapeutic dosing, which means giving too little of the active ingredient, can contribute to the development of drug-resistant heartworm strains. Moxidectin, one of the key medications used in prevention, must be delivered at a concentration high enough to fully protect against infection.
The Front Line. Products like ProHeart® 6 and Simparica Trio® contain moxidectin at levels proven to be effective against both standard and resistant heartworm strains. We recommend these two products to ensure your pet gets consistent protection and to reduce the risk of resistance spreading. We can help you decide which one is best for your pet.
The Home Front. You can help advance the fight against drug-resistant heartworms by staying consistent with your pet’s prevention schedule. Give preventives on time, every time, and follow our recommendations closely. If you miss a dose or aren’t sure whether your pet is protected, let us know, and we can help you get back on track. Annual heartworm testing is also critical, even for pets on prevention. It helps catch infections early and gives us valuable data to monitor resistance trends.
The Victory. Our goal is to prevent, protect, and preserve the health of every pet in our care. We can turn the tide in this fight to ensure a healthier and happier future for our furbabies. Together we can protect your pet and help slow the spread of resistant heartworm strains.
