Supplement to Compendium: Continuing Education for Veterinarians™ Vol. 30, No. 8(A) • August 2008 A Roundtable Discussion FELINE HEARTWORM DISEASE Understanding the Role of Heartworm Infection in Respiratory Disease in Cats Sponsored by IDEXX Laboratories and Pfizer Animal Health About the Participants Lynn Buzhardt, DVM, Moderator, a 1980 graduate of Louisiana State University School of Veterinary Medicine, is a companion animal practitioner and partner in The Animal Center in Zachary, Louisiana. She serves on the East Baton Rouge Parish Animal Control Committee, is a board member of the American Heartworm Society, conducts FDA clinical trials, and is a spokesperson for several animal health companies. Her book, Can We Have One?: A Parent’s Guide to Raising Kids, Cats, and Dogs, will be available in fall 2008. If you’re not seeing feline heartworm disease, you may be looking in the wrong Byron L. Blagburn, MS, PhD, holds the appointment of place. Feline heartworm disease does exist and is a potentially life-threatening If heartworm test results are inconsistent, distinguished university professor at the Auburn University why recommend testing to clients? College of Veterinary Medicine. He is past president of infection. It causes more problems than ever thought possible, presents numerous the American Association of Veterinary Parasitologists, Heartworm testing should be the Southern Conference on Animal Parasites, and the diagnostic challenges, and is very different from the canine disease. In light of recent considered in many cats, including Southeastern Society of Parasitologists. Dr. Blagburn was newly acquired cats, sick cats the 2001 recipient of the American Association of Veterinary research, emerging data, and the anticipated launch of the new SNAP® Feline Triple (especially those presenting with Parasitologists’ Distinguished Veterinary Parasitologist Award and the 2003 recipient of the Auburn University Student Test, several veterinary experts met to discuss the serious threat of heartworm- respiratory signs), and healthy cats Government Association Teacher of the Year award. that are going to receive heartworm associated respiratory disease (HARD), the pros and cons of the various testing preventive. Although test results in Mark Cousins, DVM, DABVP (Feline), graduated from general can be inconclusive, the Louisiana State University in 1980 and AAHA’s Veterinary methods, and the importance of heartworm prevention in cats. Management Institute at Purdue University in 1995. He SNAP® Feline Triple Test will soon started and owns New Orleans’ first exclusively feline be available to screen feline patients practice, The Cat Practice, in 1987 and is a partner in for heartworm disease. Veterinarians Chateau Veterinary Hospital in Kenner, Louisiana. The Cat Feline Heartworm FAQ and clients need to understand that Practice has won several awards, most notably the Hospital heartworm disease poses a serious of Merit Award in the September 2005 issue of Veterinary Economics and the Innovation in Business Award from the threat to cats. Testing will detect New Orleans Chamber of Commerce. Heartworm disease is rare in cats, so why should I for two critical reasons. First, diagnosis infection in a significant number of be concerned about it? is complicated and findings can be cats and therefore plays an important Ray Dillon, DVM, MS, MBA, DACVIM, received his inconsistent. A heartworm-infected cat DVM from Texas A&M University in 1973. He was the first Feline heartworm disease is more prevalent role in identifying at-risk patients recipient and continues to hold the Jack O. Rash Chair in than we once thought. Studies have shown may present with severe respiratory signs and increasing veterinarians’ and Medicine at Auburn University. Dr. Dillon is the recipient that feline heartworm infection rates likely but test negative on antigen and antibody clients’ understanding of local disease of numerous awards, including the Phi Kappa Phi Scholar tests. Ancillary tests such as thoracic prevalence. for Auburn University, Exceptional Achievement in Auburn meet or surpass infection rates for feline University Outreach, and the Beecham Award for Research leukemia. Additionally, other data have radiography, serum chemistry analysis, and echocardiography can also be inconclusive. Excellence, and was the founding president of the American suggested that the feline adult heartworm How can I convince clients to put cats, College of Veterinary Internal Medicine Foundation. infection rate can be estimated to be 20% Cats can also die suddenly with no evidence especially indoor cats, on heartworm of preexisting illness. of the canine infection rate for the same preventive? Julie K. Levy, DVM, PhD, DACVIM, graduated from the geographic area. Although prevalence studies Second, there is no approved treatment for Feline heartworm disease is an School of Veterinary Medicine at the University of California, Davis, and earned her PhD in the immunopathogenesis are ongoing, current research suggests that feline heartworm disease, so the only way incurable and potentially fatal disease. more cats are at risk than previously thought. of FIV infection at North Carolina State University. She is to protect feline patients is to initiate year- Outdoor cats are certainly at risk, but currently assigned to the small animal internal medicine round heartworm prevention early in life. mosquitoes can get indoors and expose service at the University of Florida. Her research and clinical What is HARD? All cats, even “indoor cats,” should be on indoor cats to this threat as well. In interests center on feline infectious diseases, neonatal kitten health, and humane alternatives for feline population control. Heartworm-associated respiratory disease, prevention. a recent study, 27% of heartworm- or HARD, refers to the presentation and infected cats were exclusively indoor pets according to their owners.1 As clinical circumstances associated with is the immediate past president of What is the best way to diagnose heartworm veterinarians educate clients about Tom Nelson, DVM, the death of immature adult heartworms disease in a cat? the American Heartworm Society. He earned his degree at (so-called fifth-stage larvae) or the presence protecting their indoor cats from fleas Texas A&M University and has been in private practice for Diagnosis of feline heartworm disease can of adult worms in the pulmonary arteries and intestinal parasites, heartworms 29 years. He is a partner, surgical director, and co–medical be a complicated and costly procedure. director at the Animal Medical Center of Northeast of heartworm-infected cats. need to be included among the Heartworm antigen and antibody tests parasites that continue to pose a Alabama in Anniston. Dr. Nelson was awarded the 2002 Public Relations award by the Texas Veterinary Medical have been recommended as the initial danger to indoor cats. As mentioned, Is feline heartworm disease really that dangerous? Association and is a board member of the Companion Animal diagnostic steps. Refer to the algorithm and there is no approved treatment for Parasite Council. Feline heartworm disease is potentially supporting text on pages 8 and 9 for a more feline heartworm disease, but it is more dangerous than its canine counterpart detailed discussion of diagnostic options. readily preventable. 2 Feline Heartworm Disease Supplement to Compendium • Vol. 30, No. 8(A) • August 2008 3 Estimating the Prevalence of Feline Heartworm Infection Dr. Lynn Buzhardt: Let’s begin by illustrating To answer the question about the risk of cats are antigen positive.2 Realizing that not adult heartworms is equivalent to the risk of the the significance of feline heartworm disease. in our Gainesville, Florida, community, all cats with heartworms will have a positive retroviral infections, but the risk of infection Dr. Levy, please review the information gathered we necropsied hundreds of cats after they antigen test, what is your estimate of the with immature heartworms, which we now know from your work with shelter cats in Florida. were euthanized at the local animal control number of cats with adult heartworms? cause disease, is three times as high as the facility. We were startled to find that 5% retroviral diseases. Dr. Julie Levy: My journey with feline heartworm of cats had adult heartworms, which was Dr. Tom Nelson: During 1997, 25,277 disease started when an apparently healthy feral similar to the rate of feline leukemia virus serum or plasma samples from 46 states cat died under anesthesia for neutering. A (FeLV) and feline immunodeficiency virus were submitted to Heska for feline (FIV) infection in the same group of heartworm testing.3 Of these samples, Cousins: It makes sense, and prevalency cats. We were even more surprised 15.9% were antibody positive. Miller rates confirm, that in areas where to find that about 15% of the cats and colleagues4 looked at cats Levy: It appears that the risk for infection were seropositive for heartworm from 21 areas across the country, Dirofilaria is endemic in dogs, cats are with adult heartworms is equivalent to the antibodies and that these cats suffered primarily the Northeast and going to be infected, too. risk for the retroviral infections, but the risk substantial lung disease even if there Midwest (areas not highly endemic were no adult worms. for heartworm), and found that for infection with immature heartworms, Based on the new data, we now know 12% of cats were antibody positive. which we now know cause disease, is three that the risk for heartworm infection So across the board, 12% to 16% of cats are is even greater than the risk for these antibody positive. Dr. Ray Dillon: As Dr. Levy’s work has shown, times as high as the retroviral diseases. retroviral diseases we’ve been testing for and Dr. Levy and colleagues evaluated six anti- heartworm disease is a bigger risk to cats than vaccinating against. We were beginning to body tests, and the sensitivity ranged from 32% FeLV, yet the profession has gone crazy over feel like our traditional approach to diagnosis to 89%.5,6 In my study, 50% of the cats with FeLV.