New Strategies for Canine Tick and Flea Control
Insects and acari have long presented a common and difficult challenge to companion animal veterinarians worldwide. Although effective insecticides and acaricides have been widely available for several decades, safety concerns and compliance issues have sometimes led to less than satisfying results even when best practices were followed. These arthropods cause a health concern not only because of infestation risk but also due to their ability to serve as vectors of serious, sometimes fatal, disease agents. Many flea- and tick-borne agents also infect people, creating a zoonotic disease threat.
Fleas remain the most common and important ectoparasite of pets worldwide. Reasons for our failure to eliminate the high risk of flea infestation for dogs include environmental burdens of immature stages that create an ongoing source for reinfestation, external sources of additional fleas that have not been identified, and owner behaviors including inadequate treatment1. These ongoing infestations present potentially serious health consequences for both dogs and people.
Although most dog owners are familiar with fleas, misconceptions abound about this ectoparasite and the best way to limit infestation risk. Some dog owners consider a few fleas to be normal on a pet and may not attempt to intervene until the home environment has been heavily contaminated with immature stages, while others may believe that since they do not see any fleas on their dog, treatment is unnecessary. Unfortunately, a few fleas are easily overlooked even by the most dedicated owner. Other mistakes made by pet owners include only treating once when a flea infestation is present, attempting to treat seasonally, or only treating the dog and neglecting to treat other pets in the family that may harbor active flea infestations1. All of these approaches can result in a failure to eliminate flea infestation and an ongoing canine and human health threat in the home.
Ticks have become a more urgent issue for companion animal health in many areas of the world due, in part, to wide scale geographic expansion of several tick species into new regions. As tick populations spread to new areas, the risk of disease transmission increases. Newly introduced ticks harboring tick-borne infections often catch the local community by surprise, resulting in widespread infection and disease even when vaccines and highly effective tick control products are available. Combining vaccination with tick control has been shown to dramatically reduce the risk of canine Lyme disease in endemic areas. Several acaricides, including systemic isoxazolines, have been shown to reduce or block transmission of tick-borne infections in experimental models.
One common misunderstanding among pet owners is that ticks can only be acquired from natural areas outdoors. While ticks are very common in both grassy and wooded areas surrounding homes as well as in urban and suburban parks and more natural, wild areas, one species in particular - the brown dog tick, Rhipicephalus sanguineus - thrives inside homes, kennels, and anywhere frequented by dogs. Due to the unique ability of brown dog ticks to survive long-term in the low humidity indoor environment, even dogs that spend no time in nature are at risk of acquiring severe, sometimes fatal tick infestations. All three stages feed on dogs and, when tick numbers are high, anemia and even exsanguination may result.2 Premise infestations with brown dog ticks are extremely difficult to eradicate, resulting in a long-lived nuisance for owners and pets alike3.
Controlling ectoparasites in dogs can be difficult. Although many options for flea control are available, until recently, persistent tick control options for dogs were limited to topical products, such as amitraz, fipronil, and pyrethroids. The advent of systemic isoxazolines, which provide safe and long-lived efficacy against fleas, ticks, and mites, offers new opportunities for protecting pets from the blood loss and dermatitis associated with infestation as well as reduced risk of disease transmission.
Isoxazolines have been shown capable of blocking infection with several tick-borne disease agents. Although ticks must attach to the host and begin to feed in order to acquire these systemic acaricides, some of these compounds act quickly enough to reduce or interrupt transmission4,5. Isoxazolines have also proven effective at eliminating mite infestations. Published studies to date support the use of these compounds for the treatment of demodectic mange, ear mites, and sarcoptic mange6,7. In addition, the isoxazolines provide excellent flea control, reducing flea populations and evidence of flea allergy dermatitis in naturally infested dogs.
The trend of increasing flea and tick populations and a greater risk of infections will likely continue for the next several decades. Mite infestations will similarly remain a common issue for pets. Because fleas, ticks, and some mites also create a zoonotic health risk, controlling these ectoparasites effectively has important One Health implications. Incorporating isoxazolines into routine parasite control programs for dogs brings with it the benefits of long-lived flea control, effective tick control, reduced transmission of some tick-borne infections, and the added benefit of treating or preventing mite infestations. Limiting these infestations improves the lives of animals and of people, protecting the human–animal bond and ensuring that pets remain close members of their human families.
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