Updated Feline Heartworm Guidelines: What You Need To Know
Heartworm disease has been diagnosed in all 50 U.S. states and around the globe. It is considered regionally endemic in the contiguous 48 states, Hawaii, Puerto Rico, U.S. Virgin Islands, and Guam. In addition, the movement of microfilaremic dogs and wild canids to nonendemic regions could provide a source of infection in these seemingly safe areas.
We know that cats are at risk for feline heartworm disease wherever infection occurs in dogs. In fact, heartworm antibody (HW Ab) levels nationwide appear to be in the 15–17% range. However, the condition is underdiagnosed in our feline friends. Diagnostic challenges and the tendency for cats to exhibit only transient clinical signs or die before a diagnosis is confirmed make determining the true prevalence of the condition difficult. To help veterinarians better identify and manage heartworm disease in cats, the American Heartworm Society (AHS) updated its Feline Heartworm Guidelines in November 2024.
What's in the Feline Heartworm Guidelines?
The AHS guidelines provide detailed information about heartworm epidemiology, the biology and pathophysiology of feline infections, and best practices to address prevention, diagnosis, and treatment.
The revised guidelines recommend annual heartworm testing for all cats to help diagnose infections, monitor heartworm-positive patients, establish baselines before beginning preventive treatment, and assess the heartworm risk in specific areas. They also advise using duel testing, involving antigen testing on heat-treated serum samples and antibody testing on untreated serum, to improve accuracy.
Why Dual Testing Is Necessary
Heartworm infection is often overlooked in cats because signs can be vague or nonexistent. In addition, no single test can detect every heartworm case in feline patients. Antigen tests are highly specific for adult female heartworms but won't detect an infection if only male worms or immature worms are present. Antibody tests identify the presence of antibodies in a cat's blood, which are produced by the immune system in response to heartworm exposure—however may not indicate whether the infection is currently present. This is why the revised guidelines recommend both a heat-treated antigen test and an antibody test. In some cases, additional diagnostic testing such as thoracic radiography, echocardiography, or repeat serology testing may be indicated.
Heat-Treated Antigen Testing
Documented cases have demonstrated that antigen-antibody complexes can interfere with antigen testing, leading to a false negative result. Heat treating the sample breaks down these immune complexes, releasing the antigen and providing a more accurate test result.
Antibody Testing
Antibody tests identify the presence of antibodies in a cat's blood, which are produced by the immune system in response to heartworm exposure. Unlike dogs, cats typically only have 1-2 adult worms. Clinical signs of heartworm in cats are more connected to the immature phase of the worm when antibody tests can detect an immune response. Antibody tests are only available in the reference lab currently while there are options for rapid assay tests available in clinic for feline immunodeficiency virus (FIV), feline leukemia virus (FeLV) and heartworm antigen.
Challenges in Feline Heartworm Testing Compliance
Heartworm testing is considered a standard part of preventive care for dogs, but pet owners may meet recommendations for regularly testing feline patients with hesitation. Key barriers veterinarians encounter when discussing heartworm testing with cat owners include:
- Lack of awareness: Since dogs are the primary host for heartworms, many cat owners don't realize their cats are also at risk.
- Misconceptions about indoor cats: Owners who never let their cat outside may believe their pet is safe from exposure. However, mosquitoes can easily enter homes and increase the risk of infection. In one retrospective study, approximately 25% of cats diagnosed with adult heartworms were considered indoor cats as defined by the owner.
- No approved treatment: Since no approved adulticide treatment is available for cats, owners may feel there is no point in testing.
- Financial value: Heartworm testing adds to the overall cost of the veterinary visit, and pet owners may not prioritize testing if their cat appears healthy. Unlike canine heartworm testing, which is a prerequisite for prescription preventives, many owners don't recognize the need for testing in cats. While testing for microfilariae before starting heartworm prevention is unnecessary in cats, antigen and antibody testing is strongly recommended to provide a baseline test that can be followed in the future to assure successful preventative protocols are being implemented within the household.
Tips To Improve Feline Heartworm Testing Compliance
Regular heartworm testing can detect disease early and help save lives, but you must first convince your clients this is a necessary part of their cat's health care. Clear communication, education, and strategic approaches can help improve compliance. Effective strategies for veterinary teams might include:
- Start the conversation early. Introduce heartworm testing at kitten visits and position testing as a routine standard of care instead of an optional diagnostic.
- Educate owners. Educating cat owners about the risks of heartworm disease can help them see the importance of regular testing. Address the topic with infographics, educational handouts, blogs, and social posts. Important points to highlight include:
- All cats, even those who live solely indoors, are at risk as infected mosquitoes still find their way into our homes, despite our best efforts.
- Cats often show vague signs or are asymptomatic.
- Sudden death can be the first sign of heartworm disease in cats.
- Heartworm-associated respiratory disease (HARD) can occur even if no adult worms are present.
- A single adult heartworm can be fatal in cats.
- Treatment in cats focuses on managing signs, and early detection through testing allows for better management and an improved prognosis.
- Include testing in routine preventive care recommendations. Recommend annual heartworm testing as part of each cat's routine wellness visit.
- Discuss cost concerns. Be transparent about pricing and explain that prevention is much cheaper than treating a heartworm infection.
- Offer testing incentives. Offer discounted heartworm testing during National Heartworm Awareness Month, and consider a "heartworm prevention bundle" that includes testing and a discount on preventives.
- Include the entire team. Ensure everyone in your practice can explain feline heartworm disease and the value of routine testing.
AHS continues to recommend all cats be on year-round heartworm prevention. The new recommendations can help veterinary teams identify early cases and start treatment to improve outcomes for infected cats. Download the updated Feline Heartworm Guidelines to learn more about AHS's recommendations.
