Heartworm Testing:

Screening Patients to Save Lives and Decrease Risk of Infection

By Michael H. Costello, DVM

The Impact of Heartworm Disease

Most pet owners have heard of heartworm disease but few truly understand the devastating impact it can have on their pet, and pets within their immediate vicinity. The insidious nature of heartworm disease is what makes it so devastating. Most patients show no clinical signs until the worms have done severe damage to the heart, lungs, liver and/or pulmonary arteries. Therefore, diagnosing the presence of the worms before the animal becomes ill is vital. A common and unfortunate frustration is that sudden death can be the first recognized sign of the disease, with a pet passing at home or during an anesthetic event in the clinic. Other cues that might point us towards a positive heartworm diagnosis would be coughing, fatigue, and increased respiratory rate. Therefore, even though it may not be at the top of our differential list, we need to include screening for heartworm disease when patients present with these signs. When dealing with coughing or asthmatic cats, screening for heartworm exposure should be considered before additional and sometimes invasive diagnostics are done.

To add to the complexity and frustration of heartworm disease, treating a longstanding, severe infection can be fatal. Luckily, as time has gone on, we have become more adept at avoiding the common side effects with different treatment protocols and effective staging of the disease. One of the primary reasons for staging a patient prior to treatment is to evaluate the risk of thromboemboli. The larger the worm burden, the more changes to the heart and pulmonary arteries and a patient’s activity level post treatment may influence the schedule of treatment and adjunctive therapies used. Imaging of the thoracic cavity with radiographs and/ or echocardiography are the common ways to evaluate the extent of damage to the heart and pulmonary vessels. The American Heartworm Society has some very useful resources for veterinarians and pet owners to help decide what treatments are correct for each patient. Melarsomine remains the backbone of the treatment, but the addition of pretreating with doxycycline and macrocytic lactones have improved the success rate of treatment.

We have also realized that failure to treat a patient does not only impact that pet, but those animals near the pet’s home. If a patient is not treated, this pet is now a reservoir to facilitate the spread of heartworm to other pets in the immediate vicinity. Mosquitos will bite an infected dog and now can easily infect the next dog, cat or coyote that they bite. As we as a society have become more suburban to urban, we are seeing more and more pets within smaller areas, making transmission very easy as the mosquito does not need to fly far for their next meal.

Testing for Heartworm

Luckily screening tests have become very easy to use. Testing for heartworm in dogs and cats takes a simple blood draw, and results are back before the pet leaves the clinic. This allows for safe prescription of preventatives and the chance to discuss treatment options in the same visit, should the pet have a positive result. Not only are the results fast, but the specificity and sensitivity of these point of care tests are outstanding, so confidence in the validity of the results is naturally very high. These factors, in addition to being a low-cost option, should make heartworm testing an easy proposition for your pet owner as they work with you on their pet’s regular preventative care plan. Knowing a pet’s status and the prevalence of heartworm in an area will help you and the owner determine the best parasite control regimen for that patient and the owner’s level of risk tolerance.

Sending a pet owner out the door with good news on a screening panel is a great feeling. As sad as it can be to inform someone that their pet is heartworm positive, reassuring pet owners that it is better to diagnose early on before the pet becomes ill, can help. Diagnosis of a detrimental disease is not desirable, but when it can be treated effectively, the reward is great for everyone. At the same time as benefitting a single patient, high compliance of heartworm testing also reduces the source of infection from the community. This additionally protects those pets who are not on heartworm preventative, ultimately keeping local rates of the disease lower.

Additional Benefits of Heartworm Testing

With what seems to be a never ending expansion of heartworm preventative options, we are seeing more and more combination products that not only prevent heartworm infections, but also treat or manage intestinal parasites and ectoparasites. Routine fecal screenings are still recommended, but decreasing parasite counts in patients on routine heartworm prevention is the added benefit of an all in one approach that can reduce the rates of flea and intestinal parasite infestations. In addition to protecting the patient and other pets in the environment, this management of zoonotic parasites can ultimately help mitigate the risk to humans, especially children, from being exposed.

Keep the Conversation Going

At the end of the day, it is easy to deprioritize the importance heartworm disease in areas with lower infection rates. Luckily, it can be even easier to train your staff to educate your pet owners on heartworm disease and the actions they can take to mitigate their risk. The insidious nature of this disease mandates aggressive screening to detect the infection before severe damage has occurred. Furthermore, it is with aggressive screening that we can promote awareness and limit the extent of heartworm’s local spread. When the focus is on the education of the disease, your clinic can provide even higher quality medicine, in a cost-effective manner that can increase your revenue and limit the risk to your pets and their families.

Consider Testing Alternatives

Solo Step CH and Solo Step FH Heartworm Tests are lateral flow immunoassays for the detection of heartworm antigens (canine test) and the detection of antibodies to heartworm (feline test) in serum, plasma or anti-coagulated whole blood. When only a heartworm test is warranted, Solo Step tests provide an inexpensive and extremely accurate one-step process for heartworm detection.

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