Today's Veterinary Practice

MAY-JUN 2018

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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PEER REVIEWED 14 PARASITOLOGY often target the primary reproductive host: the flea- infested dog or cat. And interestingly, failures in flea control often occur when flea-infested feral pets or flea-infested urban wildlife invade the owners' yards. But when dealing with most 3-host ticks, the problem is that the majority of the reproducing ticks are not on the dogs or cats, but on their natural wildlife hosts. Because we are limited in our ability to manage ticks on wildlife, reinfestation of pets is a common occurrence, and protracted use of acaricides as preventives is routine in many areas. Numerous studies demonstrate the high level of efficacy of the various acaricides, but the residual activity is rarely 100%, and the efficacy of products varies between and within species, even in the same laboratory. Evaluations of acaricides under natural or field conditions further illustrate that although efficacy is good, it is not 100%. For instance, in a field efficacy trial conducted in Kansas, an imidacloprid (8.8% w/w)-permethrin (44.0% w/w) formulation was evaluated on dogs against naturally occurring populations of A. americanum. When dogs were walked in a naturally tick-infested environment, the 48-hour postexposure efficacy of the imidacloprid-permethrin formulation was 93.5%, 98.9%, 94.6%, 94.1% and 96.6% on days 3, 7, 14, 21 and 28, respectively, post treatment.8 Variation in product efficacy also occurs. In 2 studies conducted at Kansas State University, different results were found when evaluating the efficacy of acaricides against Dermacentor variabilis infestations in dogs from 2 different regions of the United States. 9,10 In the first study, the efficacy of imidacloprid-permethrin and fipronil–(S)-methoprene formulations was evaluated against a D. variabilis isolate from California. The 48-hour postinfestation efficacy on day 30 post treatment was 92.0% and 83.2%, respectively, for the imidacloprid-permethrin and fipronil–(S)- methoprene formulations.9 In the second study, the 48-hour postinfestation efficacy on day 30 for the imidacloprid-permethrin and fipronil–(S)-methoprene formulations against a D. variabilis isolate from Oklahoma was 17.5% and 75.7%, respectively. 10 Recently, a new class of insecticide/acaricide has provided the first orally administered approach to tick control. Afoxolaner, fluralaner and sarolaner are members of the isoxazoline class and work by inhibiting GABA and glutamate-gated chloride channels, leading to hyperexcitation and death of insects and arachnids. 11-13 METHODS OF COMBATTING TICKS Understanding Tick Ecology in Your Area Because tick control can be extremely difficult and because ticks are vectors of a variety of bacterial and protozoal diseases, veterinarians should have an understanding of the ecology of the tick(s) encountered in the area in which they practice. Veterinarians need to be educated on the various aspects of tick ecology, disease transmission and control methodologies so they can then educate their staff and pet owners. CAPC, a leading parasitic content provider, offers client and staff education resources available at capcvet.org and petsandparasites.org . Managing Pet Owner Expectations Because 100% tick kill is rarely achievable, perceived efficacy of acaricides may be directly related to the numbers of ticks to which dogs are exposed. If a dog is treated with one of these highly efficacious acaricides and encounters just a few ticks, it is likely that all those ticks will be killed. However, if tick exposure is considerably larger, expect a few ticks to be observed on these dogs, and pet owners may perceive a lack of efficacy. Therefore, in areas where tick populations are increasing, the perception may be that the products are not as effective as they once were. Pet owners often view tick infestations of their pets differently than flea infestations. 12 Whether this is because of concerns about tick-transmitted diseases or simply a phobia, the presence of a couple of ticks on the pet often elicits a more pronounced negative reaction than the presence of a couple of fleas. A 95% effective flea product may provide great client satisfaction, while a similarly effective tick product may be perceived as a failure. Therefore, it is not uncommon for label-recommended application of a product to not appear to control the problem. This result may be real or perceived, based on pet owner expectations of product performance. Given pet owner concerns, a need to reduce tick-borne disease and a lack of 100% efficacy, occasionally additional control measures are needed. If additional control measures are deemed necessary, pet owners need to be educated as to why such measures are necessary and notations made in the

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