American Heartworm Society updates feline guidelines

Photo: Pee Paew/Adobe Stock

The American Heartworm Society (AHS) has updated their Feline Heartworm Guidelines for veterinarians. The guidelines—last revised in 2015—addresses persistent underdiagnosis and undermanagement of heartworm disease in cats, and provides more robust data on prevention, testing and treatment, according to AHS.¹

The guidelines update was spearheaded by a committee of AHS board members. The revisions were completed after a thorough scientific review by experts from the fields of parasitology, cardiology, and clinical practice. It includes revised advice on heartworm screening, mosquito control and treatment options for heartworm-positive cats.¹

Feline heartworm disease can be life-threatening. It starts with a bite from a mosquito infected with the parasitic worm Dirofilaria immitis, allowing heartworm larvae to enter the cat’s bloodstream. The larvae thrive and develop in subcutaneous tissues before moving into muscle tissues, the heart, lungs and arteries.²

Immature worms’ arrival into the small arteries in the lungs initiates a severe inflammatory response that damages not only the arteries, but also the bronchioles (small airways) and alveoli, according to Cornell University College of Veterinary Medicine in Ithaca, New York. “Between 60 and 100 days after the initial infection, you can start to see signs of pathology in an affected animal’s body, even though the parasite has not yet reached maturity,” Dwight Bowman, DVM, PhD, a professor of parasitology at Cornell, said on the university’s website. ²

The revised AHS guidelines recommend routing heartworm screening for cats. The 4 primary reasons for screening, according to the AHS, are as follows¹:

• to help establish a diagnosis when a veterinarian finds clinical evidence of infection;
• to monitor the status of cats already diagnosed with heartworms;
• to establish a baseline prior to beginning a heartworm prevention product;
• and to better understand the relative risk of feline heartworm in a practice area.

“While dogs are routinely screened for heartworms during annual check-ups, testing in cats has primarily been limited to cases when a veterinarian suspects heartworm infection based on a cat’s clinical signs,” Jennifer Rizzo, DVM, president of AHS, said in a news release.¹ “With so few cats tested, it has been difficult for veterinarians to get a handle on the true incidence of heartworm in cats—even though cats are at risk wherever heartworm infection occurs in dogs.”

According to the revised guidelines, cats should be screened using both antigen and antibody tests. The AHS further recommends that veterinarians conduct antigen tests with heat-treated serum, which differs from their canine guidelines. Heat-treated serum dissociates potential antigen-antibody immune complexes and helps obtain the most accurate results. The second component of heartworm screening in cats is antibody testing.¹

Other diagnostic techniques outlined in the revised guidelines include radiography, echocardiography and point of care ultrasound.¹ “There’s no question that testing limitations have been a significant factor in heartworm underdiagnosis in cats,” Rizzo acknowledged in the release. “By using the most accurate screening procedures and screening cats on a more routine basis, we hope to greatly improve the veterinary profession’s understanding of the disease and initiate steps to best manage affected patients.”

With more routine testing, the AHS says its experts expect the numbers of cats diagnosed with heartworms to increase. Treatment objectives are to relieve the clinical signs of disease and, in the case of adult infections, to prevent sudden death of the cat.¹ “While no approved adulticide treatment is available for cats, our guidelines include updated recommendations for managing infected cats,” Rizzo said.

Several classes of medications, along with dosages, are described in the revised guidelines, from anti-inflammatory drugs to leukotriene modifiers to antibiotics, according to AHS. Techniques for surgical removal of adult heartworms are also described in the revised guidelines.¹

Meanwhile, the AHS guidelines continue to recommend that all cats be on year-round heartworm prevention with a macrocyclic lactone product. However, the revised guidelines now also address the importance of vector control as well as preventive products. The goal of vector control in cats should be to reduce the risk of mosquitoes in the environment rather than on cats themselves, according to AHS.¹

“As an organization dedicated to reducing the incidence of heartworm disease and its impact on pets, the AHS has long been concerned about the underdiagnosis and undermanagement of heartworm disease in cats,” Rizzo said. “Fortunately, we now have scientific information that supports a more proactive approach to heartworm diagnosis, as well as greater specificity in prevention and treatment approaches.”

The revised guidelines can be accessed on the AHS website at heartwormsociety.org/guidelines.

References

1. American Heartworm Society announces updated guidelines on management of feline heartworm disease. News release. American Heartworm Society. November 12, 2024. Accessed November 13, 2024. https://www.heartwormsociety.org/in-the-news/910-american-heartworm-society-announces-updated-guidelines-on-management-of-feline-heartworm-disease
2. Cornell Feline Health Center. Heartworm in cats. Cornell University College of Veterinary Medicine. Accessed November 13, 2024. https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/heartworm-cats