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Clarke Atkins, DVM, Diplomate ACVIM (Internal Medicine & Cardiology), <\/em> The author discusses new information on some of the most important issues faced by practitioners today, including: Development of heartworm resistance to common preventives, complexities of feline heartworm, and the role of Wolbachia in the heartworm complex.<\/p>\n The 14th Triennial Heartworm Symposium, which took place September 8 through 10, 2013, in New Orleans, was one of the most important scientific meetings held in the 40-year history of the American Heartworm Society (AHS).<\/p>\n In recent years, significant work has been undertaken to better understand the most important issues faced by practitioners today, including:<\/p>\n New information on these topics, as well their connection to the challenges of compliance, owner education, and shelter medicine, sparked lively discussion in New Orleans.<\/p>\n The 14th Triennial Heartworm Symposium was attended by scientists and clinicians from 13 countries, with more than 50 sessions and posters presented. To read the “Symposium Snapshot,” visit heartwormsociety.org\/veterinary\u2011resources\/AMHS_Symposium.pdf.<\/p>\n In addition, the AHS website features videos of interviews with key speakers, including Drs. Wallace Graham, Clarke Atkins, Laura Kramer, Matt Miller, Ray Dillon, and Byron Blagburn; watch the videos at heartwormsociety.org\/veterinary-resources\/interviews-with-experts-from-the-2013-heartworm-symposium.html.<\/p>\n Scientific papers from the symposium will be published in a future issue of the Journal of Veterinary Parasitology<\/em>.<\/p>\n<\/div>\n For the past 10 to 15 years, heartworm experts and practitioners have become concerned that Dirofilaria immitis<\/em> (heartworm) may be developing resistance to our current macrolides and avermectins, also known as macrocyclic lactones<\/em> (MLs) (Table 1<\/strong>). Concern for decreased efficacy exists for all MLs.<\/p>\n These concerns have resulted in lively debate regarding the role of resistance in apparent lack of efficacy (LOE) reports emanating from the Mississippi Delta region (Figure 1<\/strong>).<\/p>\n It is now accepted that heartworm resistance to preventives, a class effect, has been documented, apparently in small pockets, both in and outside the Mississippi Delta. However, the true incidence of resistance is unknown at this time. According to Ray Kaplan, DVM, PhD (University of Georgia), we know very little about the development of heartworm resistance. We do know that it is different from that which occurs in livestock gastrointestinal nematodes.<\/p>\n The practice of \u201cslow kill\u201d (also called \u201csoft kill\u201d or \u201ctrickle kill\u201d)\u2014killing adult heartworms with long-term, monthly use of a preventive dosage of ivermectin\u2014has been implicated in the development of heartworm resistance. However, this is an area of controversy.<\/p>\n Resistance has occurred with all 4 licensed ML molecules, though not all products are equal in this regard. Imidacloprid\/moxidectin topical has been demonstrated to be more effective in preventing heartworm infection (HWI) by 2 resistant isolates, as compared to other ML chemicals and formulations, but the overall clinical importance of these findings remains to be determined.1<\/sup><\/p>\n While more research is needed to better understand resistance, it is clear that client adherence (compliance) remains the major factor involved in the Mississippi Delta dilemma. In a recent study, only 1% to 3% of reported putative LOEs in the region were truly supported by product failure.2<\/sup><\/p>\n Therefore, based on our current knowledge, the best course of action is to continue recommending on-label use of heartworm preventives, 12 months per year. Preventives are effective in the vast majority of patients and represent the best protection currently available to pets.<\/p>\n In the meantime, work is underway to develop a genetic test that will help veterinarians determine the relative risk of heartworm resistance in their practice areas. In addition, the AHS released a revised statement on heartworm resistance, available at http:\/\/www.heartwormsociety.org\/pdf\/Resistance_statement_FINAL.pdf.<\/p>\n Wolbachia<\/em> (Figure 2<\/strong>) is a critical component in the well-being, long-term survival, and reproduction of heartworms and, therefore, plays an important role in the treatment of HWI:<\/p>\n For these reasons, the AHS guidelines for treatment of adult heartworms (see Updated AHS Guidelines<\/strong>) call for treatment with the antibiotic doxycycline prior to administering melarsomine in order to reduce post-adulticide side effects.<\/p>\n Laura Kramer, DVM, PhD, Diplomate EVPC (University of Parma, Italy) noted in her presentation that doxycycline can be combined with an ML to create an alternative adulticide. While she combined doxycycline and ivermectin, similar studies have used moxidectin instead.<\/p>\n This combination of doxycycline and ivermectin:<\/p>\n Veterinarians have known for some time that heartworm disease (HWD) presents differently in cats than dogs and that heartworms mature and reproduce less frequently in cats. In fact, feline HWD is under-recognized by veterinarians and more common than originally thought.<\/p>\n Cats can develop a condition known as heartworm-associated respiratory disease<\/em> (HARD), which results in significant lung damage, cough, wheezing, and dyspnea, when developing stage 5 filarids are eliminated and no mature adult heartworms are present.<\/p>\n HARD, as used here, is different than the HWD produced by adult D immitis<\/em> (Table 2<\/strong>). In HARD, heartworms die before maturing (early in stage 5 or immature adult stage) and producing antigen, making diagnosis challenging. Cats affected with HARD are typically antigen-negative, but antibody-positive and, while radiographic lesions are typically present, absence of adult worms renders cardiac ultrasound nondiagnostic.<\/p>\n Ray Dillon, DVM, MS, MBA, Diplomate ACVIM (Auburn University) explains that diagnosis of (mature) feline HWD and HARD is further complicated because other feline parasites, including Toxocara cati<\/em> and Aelurostrongylus abstrusus<\/em>, can cause lung disease similar to that induced by heartworms. He also noted that, while broad-spectrum preventives for heartworm and intestinal parasites prevent roundworms in the gastrointestinal tract of cats, they do not appear to prevent roundworm migration to the lungs.<\/p>\n Matt Miller, DVM, MS, Diplomate ACVIM (Cardiology) (Texas A&M University), demonstrates that some radiographic changes due to feline HWD are detectable and relatively specific, leading to a diagnosis of feline HWD (Figure 3<\/strong>). Radiography can also help rule in\/out other diseases, such as neoplasia, foreign body, thoracic trauma, and heart failure.<\/p>\n Animal shelters deal with extremely large volumes of animals, and many shelters face significant challenges when it comes to prevention and treatment of HWD due to the high prevalence of HWD in animals under their care and availability of little to no medical history. In addition, funding often is minimal, and staffing resources are generally limited.<\/p>\n Katherine Polak, DVM, MPH, MA (University of Florida), explains that many shelters are unable to follow the AHS guidelines. For example, the shelter team may:<\/p>\n In addition, dogs sometimes test negative for heartworms and are adopted, only to become antigen-positive on the next retest.<\/p>\n There are no easy solutions for these challenges, but the AHS is working toward connecting shelter veterinarians with informational resources that will help them provide the best possible care for patients with HWI\/HWD. This will be a topic of discussion for the AHS this year (2014).<\/p>\n HWD is arguably the most significant disease in small animal medicine, with an estimated 1 million dogs and an unknown number of cats affected. The 2013 Triennial Heartworm Symposium gave attendees a unique, firsthand opportunity to learn the latest about this serious disease. Practitioners and other veterinary professionals are urged to visit heartwormsociety.org<\/a> for more information about the symposium, heartworm client educational resources, and HWI. n<\/p>\n AHS = American Heartworm Society; HARD = heartworm-associated respiratory disease; HW = heartworm; HWD = heartworm disease; HWI = heartworm infection; LOE = lack of efficacy; ML = macrocyclic lactone<\/p>\n
\nNorth Carolina State University<\/em><\/p>\n
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More from the 14th Triennial Heartworm Symposium<\/h2>\n
LACK OF EFFICACY & HEARTWORM RESISTANCE<\/h2>\n
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<\/p>\nDocumentation of Resistance<\/h3>\n
Resistance Development<\/h3>\n
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Product Efficacy<\/h3>\n
Adherence Importance<\/h3>\n
Updated 2014 AHS Guidelines<\/h2>\n
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WOLBACHIA<\/em> & DOXYCYCLINE<\/h2>\n
Wolbachia\u2019s<\/em> Role in Treatment<\/h3>\n
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<\/a><\/p>\nCombination Adulticide Therapy<\/h3>\n
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FELINE HEARTWORM DISEASE<\/h2>\n
HARD Syndrome<\/h3>\n
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<\/a><\/p>\nRole of Radiography<\/h3>\n
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<\/a><\/p>\nHEARTWORM DISEASE IN ANIMAL SHELTERS<\/h2>\n
The Care Gap<\/h3>\n
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Connecting Shelters& Resources<\/h3>\n
IN SUMMARY<\/h2>\n
Suggested Reading<\/h3>\n
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<\/a>Clarke Atkins<\/strong>, DVM, Diplomate ACVIM (Internal Medicine & Cardiology), is the Jane Lewis Seaks Distinguished Professor of Companion Animal Medicine at North Carolina State University. He is also a member of the Today’s Veterinary Practice Editorial Peer Review Board and American Heartworm Society’s Executive Board. Dr. Atkins’ research involves canine and feline heartworm disease and pharmacologic therapies for cardiac disease; he received the 2004 Norden Award for excellence in teaching.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"