Study: Surprising findings about heartworm in shelter cats and dogs

Cat and dog together on white backgroundAre you testing dogs in your shelter for heartworm? How about cats? How confident are you that the tests you’re using aren’t letting some pets slip through the cracks? A new study found that, despite availability of preventives, 1 in 4 dogs and 1 in 5 cats taken in as strays to Florida shelters have been infected.

“This confirms suspicion that many animals are still not receiving even the basic health care they need, likely driven by the cost of care, veterinary care deserts, and lack of owners understanding what care is needed to keep their pets healthy,” said Dr. Julie Levy, the Fran Marino Professor of Shelter Medicine Education at UF and one of the study co-authors.

“This creates problems for shelters since they receive many animals with unknown histories, heartworm tests are imperfect, and missing infections can lead to lung and heart damage and further spread to other animals.”

Existing tests target different stages in the life cycle of the heartworm. Antibody tests (Ab) can deliver positive results for past or current infections with third or fourth stage larval infections; angtigen (Ag) and microfilaria (Mf) tests detect adult worm infections.

The researchers tested 100 dogs and 100 cats from three Florida animal shelters. All of the animals were strays at least two years of age and without any known history of heartworm preventive medication. The veterinary student researchers learned Fear Free handling techniques and used treats and cuddles while collecting blood for a panel of test methods. The test results were shared with the shelters for the pets’ medical files.

The study was conducted by several UF-affiliated researchers, including Kellie Hays and Jennifer Lane, student researchers working under the direction of Dr. Levy; Drs. Maria Serrano and Simone Guerios, colleagues in UF’s Shelter Medicine student rotation at Miami Dade Animal Services; as well as Dr. Annette L. Litster, former director of Maddie’s Shelter Medicine Program at Purdue University. Their findings included:

  • Heat treatment of serum from dogs increased detection of heartworm. (Read more about heat treatment here.)
  • The Ag or Mf tests showed dogs more likely to be infected than cats, however, when evidence of exposure was shown by a positive Ab test, the prevalence was about the same. This indicates cats tend to have larval adult infections that usually recognized, which is important because a lasting and even life-threatening respiratory disease can result from even brief infection with larval stages in cats.
  • Given cats have a similar, high risk of infection to dogs in Florida, heartworm preventives should be given to cats in areas where heartworm transmission occurs.

The authors concluded, “Shelters in high prevalence areas should prioritize allocation of resources for heartworm screening and prevention, especially for animals being transported to low prevalence areas of the country, where awareness of HW screening and prevention could be suboptimal.”

Kellie M. Hays, Jessica Y. Rodriguez, Susan E. Little, Annette L. Litster, Kennedy K. Mwacalimba, Kellee D. Sundstrom, Deborah M. Amodie, Maria A. Serrano, Simone D. Guerios, Jennifer N. Lane, Julie K. Levy, Heartworm prevalence in dogs versus cats: Multiple diagnostic modalities provide new insights, Veterinary Parasitology: X, Volume 4, 2020, 100027, ISSN 2590-1389,