Heart Worm Prevention
April is Heartworm Prevention Month! It’s a huge topic in pet care, but many may not think about the potential impact on their pets quality of life. Heartworms are insidious in that many pets go a very long time without showing any symptoms. All the while, they are shedding juvenile heartworms and having ever increasing damage to their heart.
Why be concerned?
Heartworms cause serious damage to not just the heart, but also lungs and other organs, through the release of toxic chemicals when the heartworm dies. Spread through the bite of an infected mosquito, larvae travel through the bloodstream and mature into adults in cardiac tissue. Heartworms live in more than just cats and dogs. They also live in ferrets, foxes, wolves, coyotes, and sea lions. So even though you may not live near any other pets, because wild species live in proximity to many urban areas, they are considered important carriers of the disease.
Interestingly in cats, heartworms do not live as long (2-4 years), grow as large, or produce as many adults when compared to heartworms in dogs. Even though a cat may only have 1-2 heartworms, given their relative body size, a cat with only a few heartworms is still considered heavily infected.
Stages of Heartworm Disease
There are four classes, or stages, of heartworm disease. The higher the class, the worse the disease and the more obvious the symptoms.
Class 1: No symptoms or mild symptoms such as an occasional cough.
Class 2: Mild to moderate symptoms such as an occasional cough and tiredness after moderate activity.
Class 3: More severe symptoms such as a sickly appearance, a persistent cough, and tiredness after mild activity. Trouble breathing and signs of heart failure are common. For class 2 and 3 heartworm disease, heart and lung changes are usually seen on chest x-rays.
Class 4: Also called caval syndrome. There is such a heavy worm burden that blood flowing back to the heart is physically blocked by a large mass of worms. Caval syndrome is life-threatening and quick surgical removal of the heartworms is the only treatment option. The surgery is risky, and even with surgery, most dogs with caval syndrome die.
Treatment and Prevention
Treatment is kind to neither the pet nor the pocketbook. The drugs used for treatment are toxic to the pets body and can have serious complications, such as blood clots in lungs. Injections of Melarsomine, an arsenic-containing drug that is FDA-approved to kill adult heartworms, are given deep into the back muscles through multiple rounds. Other drugs can kill the larvae in the blood stream.
To avoid the need to treat your pet, prevention is key. There are many FDA-approved products to prevent heartworms. All do require a vet prescription, so make sure you’re talking with your vet about what’s going to work best for your pet. There are liquid products applied topically, chewable tablets, and ones administered sub-dermally every 6-months. Puppies as young as 7 months can start on heartworm prevention, and it’s recommended to begin yearly testing after that. If your pet has not been on heartworm prevention, you must get them tested before you begin giving them prevention medications. This is because prevention medications are not meant to treat current infections and may actually lead to more complications and side-effects.
Thankfully, people cannot get heartworms from their pets. Heartworms are only transmitted by the bite of an infected mosquito. In rare cases, people can get heartworms after being bitten by an infected mosquito, but because people are not a natural host for heartworms, the larvae usually migrate to the arteries of the heart and lungs and die before they become adult worms.
