What’s the big deal about heartworm disease?
You may have heard your veterinarian mention heartworm disease, or recommend a monthly preventive medication. Perhaps your dog has a heartworm test as part of her annual exam, and you’ve wondered, “what’s the big deal about heartworm disease? Is all this really necessary?” In short: yes. Heartworm is a very serious disease, so these preventive steps are important.
Let’s take a few minutes to answer some common question.
What is the disease?
Heartworm disease is just what it sounds like: worms that live in the heart. Doesn’t sound very appealing, does it? Well, it’s even less appealing than it sounds. These worms can grow up to a foot long, and can migrate to animal’s heart, lungs, and blood vessels. They can live up to 7 years in dogs, and about 2 to 3 years in cats. An unprotected animal has the potential to contract more and more worms each year.
Without treatment, heartworm disease can be fatal!
Yikes! That’s scary. How does that affect the animal?
It depends on the type of animal, and how long they’ve had the disease. In dogs, it’s possible for many worms to grow, mature, and reproduce inside the body. Sometimes, these worms can number in the hundreds. Dogs with a low worm burden may show few signs, or none at all. As the disease progresses, signs can become more dramatic. An owner may note a cough, decreased activity level, exercise intolerance, or decreased appetite or weight.
Damage occurs to the animal’s heart and lungs. As more worms grow, the dog may develop heart failure, or even a complete blockage (leading to collapse and death without intervention).
In cats, most worms do not survive to maturity. An affected cat may have just a few adult worms, or none at all. But the lack of adult worms doesn’t mean these kitties get away unscathed…quite the opposite. Even the immature form of the organism can cause significant respiratory disease. An affected cat may cough, wheeze, or have difficulty breathing. He may have non-specific signs (like a decreased appetite or activity level, weight loss, or intermittent vomiting). It’s possible to see things like weakness, trouble walking, or fluid in the belly. Sometimes a cat will show no signs at all, or will not seem abnormal until a dramatic collapse or sudden death.
You’ve mentioned dogs and cats…what types of animals can contract heartworm disease?
In small animal veterinary medicine, we are usually talking about heartworm disease in the context of pets (it can be contracted by dogs, cats, and ferrets). But wild mammals (such as coyotes, wolves, and foxes) can also carry the disease. In extremely rare instances, it has been noted in humans.
Dogs are natural hosts, and cats are atypical hosts. For this reason, the disease behaves differently in dogs v. cats.
So how do these animals become infected, anyway?
Heartworm is transmitted by mosquitoes. An adult (female) worm living in a host animal produces offspring (the immature form of heartworms are called microfilaria). These microfilaria circulate in the host’s bloodstream. When a mosquito bites the infected animal, it contracts the microfilaria. In the mosquito, the microfilaria mature to infective stage larvae. Then, when the mosquito bites another animal, the larvae are transferred to that animal. These larvae mature into adult heartworms within the newly infected animal in about 6 months.
I’ve heard that heartworm is a big problem in the South. I don’t live in the South…is my pet safe?
It’s true that heartworm is, unfortunately, very common in the southern United States. However, we in the Northeast are not unaffected.
We absolutely see cases of heartworm disease in Morris County. In fact, heartworm has been documented in all 50 states. Not to mention, through adoption, many dogs in the North have been re-homed from Southern states.
This all sounds terrible! How can I protect my pet?
The good news is that we have many good options for heartworm prevention in our pets. These medications are obtained by prescription only, and can be dispensed or prescribed by a veterinarian. For dogs, there are oral, topical, and injectable products which provide excellent protection when given as directed. Most of these medications are given monthly, and also provide treatment for intestinal parasites (worms that live in the GI tract). For dogs, choose a flea and tick product that also provides protection from mosquitoes. For cats, we have a good topical product, which provides protection from heartworm, fleas, and common intestinal worms. Talk with your veterinarian about which medication would be the best fit for your pet.
The American Heartworm Society recommends heartworm preventive 12 months a year. Dogs should be on heartworm prevention by the time they turn 8 weeks old.
As heartworm disease is transmitted solely by mosquitoes, limiting your pet’s mosquito exposure also limits her risk of heartworm. Try to eliminate mosquito breeding grounds by removing standing water from your pet’s environment, and washing outdoor water bowls daily. Do not allow containers such as kiddie pools, bird baths, and buckets to be reservoirs of standing water. Keep screens in your windows and doors in the warm months.
It takes only a few drops of blood to test a pet for heartworm disease. The American Heartworm Society also recommends testing pets for heartworm disease every 12 months. Puppies, dogs who have missed heartworm doses, and those who have not previously been on heartworm prevention will require more frequent testing.
The earlier heartworm disease is detected, the better a chance that animal has of making a good recovery. A newly infected animal rarely shows signs of infection, so early detection with a blood test is imperative in diagnosing and treating that pet. Furthermore, it can be dangerous to a pet to administer heartworm prevention if they are currently infected with heartworm disease. Therefore, we must be sure of a negative heartworm status before giving the preventive medication.
While the heartworm preventive medications are extremely effective, there are rare cases of failure. In addition, a lapse in coverage for any reason (such as missing doses, giving expired medication, or giving doses late) could leave a pet unprotected and vulnerable to heartworm disease. It’s also possible for pets to vomit up, spit out, or rub off their preventive medication, thus leaving themselves vulnerable.
For these reasons, it is important to test dogs every 12 months at a minimum. Dogs over 7 months of age need to be tested prior to beginning heartworm prevention, and then again 6 months after starting.
What should I do if my pet is not currently on heartworm prevention?
Contact your veterinarian, have your pet tested, and begin preventive medication if the test was negative for heartworm disease. Continue year-round heartworm prevention. Retest in 6 months, and every 12 months after that.
What if my pet contracts heartworm disease?
Dogs: A dog who has tested positive for heartworm disease will require follow-up testing to verify the diagnosis. If the diagnosis is accurate, the dog will need to be severely exercise-restricted to limit risk of further heart and lung damage. Some dogs need to be stabilized before the heartworms can be directly addressed. Once the pet is deemed stable, your veterinarian will be begin a treatment protocol including many months of oral and injectable medications.
These medications will be chosen based on your pet’s needs, and the presence of any clinical signs. Your dog should be re-tested 6 months after treatment, and kept on tear-round prevention for life. While heartworm infections in stable dogs can be treated, the treatment protocol is prolonged and not without risk or expense. Prevention is preferable compared to treatment.
Cats: There is no treatment for heartworm disease in cats. If a cat is diagnosed with heartworm disease, the goal is to provide supportive care and protect that cat as best as possible from the potential side effects of infection. In some cases, the worm(s) may be removed surgically. Unlike in dogs, some heartworm infections may resolve spontaneously (though a cat may still suffer from damage to his respiratory system). A major danger to an infected cat is the adult worms dying in his body, which can trigger an allergic reaction, blood clots, or inflamed lungs. The worms may also migrate to other parts of the cat’s body. These cats will need to be monitored closely.
Although heartworm disease can be a scary prospect, by testing annually and being sure to administer prevention 12 months a year, you can help protect both your beloved pet and yourself from a broken heart.
Pet Owner Resources (American Heartworm Society)