Canine heartworm prevention and broad-spectrum internal parasite control (Sponsored by Virbac Animal Health)
Broad-spectrum internal parasite preventives decrease the potential for disease in animals and people by eliminating roundworms, hookworms, and tapeworms from dogs. The life cycle of heartworms, pet owner compliance, and properties of broad-spectrum heartworm preventives all may affect successful heartworm prevention and internal parasite control. So all should be considered when selecting products and implementing a comprehensive control program.
Heartworm life cycle
Transmission of heartworms begins when mosquitoes ingest Microfilaria from an infected dog. Microfilaria then migrate to the mosquito's excretory system and develop to the infective third stage larva. When infected mosquitoes feed, they deposit larvae at the skin surface. Larvae enter the mosquito bite wound and begin migrating to heart and pulmonary arteries.1 Adult heartworms reach sexual maturity at six to 6.5 months. Female worms release Microfilaria after mating and fertilization. Heartworms are known to live and continue to produce Microfilaria for up to seven years. Microfilaria can survive in infected dogs for up to two years.Client compliance
Given the complex interplay between the heartworm developmental cycle, diagnostic testing, and treatment and prevention strategies, it is easy to see why achieving successful heartworm diagnosis, treatment, and prevention can be challenging. One of the biggest obstacles is client compliance. Recent surveys indicate that pet owners often do not use heartworm preventive medications regularly or reliably.2 In addition, more than 250,000 dogs are diagnosed with heartworm infection each year, and surveys of clinic dispensing records indicate that pet owners often do not receive the amount of heartworm preventive necessary to protect all pets in a household for the entire year.3 Compliant use of these products will allow us to achieve a level and spectrum of internal parasite control that was previously unachievable. Given the potential for disease in animals and people, and the variations in climate in all U.S. regions from year to year, the best approach to comprehensive parasite control is year-round prevention. Veterinarians must communicate to clients that because heartworm transmission periods vary markedly from region to region and from year to year, our only assured strategy for preventing heartworm infection is to emphasize compliant, year-round use of preventives. Compliant use of broad spectrum heartworm preventives also protects pets from parasites.
Current heartworm preventives like IVERHART MAX® (ivermectin/pyrantel pamoate/praziquantel) (Virbac Animal Health)†* belong to the macrocyclic lactone class of endectocides, which includes ivermectin, milbemycin oxime, moxidectin, and selamectin. Macrocyclic lactones exert their effects by targeting a group of ion channels unique to invertebrates.
Broad-spectrum parasite control products are now available in oral, topical, and injectable formulations and have activity against one or more potentially zoonotic internal parasites. Newer combination products are also effective against tapeworms. Tapeworms such as Dipylidium caninum and Taenia pisiformis are common and may cause signs of gastrointestinal disease in infected dogs. D. caninum also may infect humans, especially children, and can be a cause of considerable alarm among parents and care-givers when proglottids are passed in feces or are found in soiled diapers. The Companion Animal Parasite Council (CAPC) recognizes the importance of zoonotic internal parasites and recommends year-round use of heartworm preventives with efficacy against zoonotic internal parasites. For more information on CAPC, visit http://www.capcvet.org/.
* Virbac Animal Health's IVERHART MAX® Flavored Chewables is a broad-spectrum, once-a-month internal parasite preventative. Please consult package insert for complete product information. Indications: For use in dogs to prevent canine heartworm disease by eliminating the tissue stage of heartworm larvae (Dirofilaria immitis) for a month (30 days) after infection and for the treatment and control of roundworms (Toxocara canis, Toxascaris leonina), hookworms (Ancylostoma caninum, Uncinaria stenocephala, Ancylostoma braziliense), and tapeworms (Dipylidium caninum, Taenia pisiformis).
† All dogs should be tested for heartworm infection before starting a preventative program. Following the use of IVERHART MAX® Flavored Chewables, digestive and neurological side effects have rarely been reported. Use with caution in sick, debilitated, or underweight dogs weighing less than 10 lbs.
1. Kotani T, Powers KG. Developmental stages of Dirofilaria immitis in the dog. Am J Vet Res 1982;43:2199-2206.
2. American Animal Hospital Association (AAHA). The Path to High-Quality Care: Practical Tips for Improving Compliance. Lakewood, Colo. AAHA Press, 2003.
3. Cummings J, Vickers L, Marbaugh J. Evaluation of veterinary dispensing records to measure "clinic compliance" with recommended heartworm prevention programs, in Proceedings.
Dr. Jason McFarland