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Veterinarian Technician March 2011 (Vol 32, No 3)

Preventing Canine Tick-borne Diseases

by Ryan Cheek, RVTg, VTS (ECC)

    Evidence of ticks spans approximately 200 million years, making them one of the most successful groups of arthropods on Earth.1 Ticks are found in all parts of the world, except Antarctica; prey on all classes of vertebrates, except fish; and were known to transmit etiologic agents of disease well before it was known that mosquitoes and fleas transmit disease. After mosquitoes, ticks are the second most important disease-causing arthropod around the world and the most important in the United States (TABLE 1) .1

    Several factors have affected the incidence and prevalence of tick-borne diseases among dogs:

    • People are moving to, or vacationing in, rural areas with pets, which can increase exposure of pets and their owners to ticks.
    • Many people do not regularly remove leaf litter, bushes, or native vegetation from their properties. Studies have shown that the tick population around a home can be reduced by 72% to 100% through basic environmental control.2
    • People draw wildlife onto their properties, which can increase the tick population. Most ticks that cause disease in dogs are three-host ticks, meaning that they require three hosts to complete a life cycle. Common hosts of ticks include deer and rodents (e.g., squirrels, chipmunks, mice), which are common in residential areas. In addition, pet owners allow their pets to roam in forested areas, exposing their pets to ticks.
    • Many individuals and communities no longer use environmental pesticides, which have helped control the tick population for many years.2

    Control of tick-borne disease in dogs is complex, involving (1) control of ticks on dogs and (2) elimination or reduction of diseases that ticks transmit (the latter is beyond the scope of this article). Methods of tick control include chemical agents, area-wide acaricides, biologic control, habitat modification, and host manipulation. Whenever recommending use of an acaricide—whether area wide or directly on a pet—the veterinary team must emphasize correct use of the product. Compliance is key to helping prevent tick resistance to the chemical and to protect the environment.

    Chemical Agents

    Numerous products that are applied directly to pets can help to control ticks. These products can be purchased over the counter or through veterinary sources and may be applied topically, sprayed on, or impregnated in a collar. Common examples of chemicals that are used to control ticks on dogs are pyrethrin, permethrin, amitraz, phenothrin, cyphenothrin, and fipronil.2 These chemicals can protect dogs from tick-borne diseases in the following ways.

    Repellency has two forms:

    • In contact repellency, a tick comes into contact with a chemical and then moves away from the host without biting.
    • In noncontact repellency, a chemical prevents a tick from making contact with a host. DEET is an example of a noncontact repellent, but it is not approved or labeled for use on dogs.

    Repellents are not meant for long-term prevention; they are typically effective for several hours and should not be used every day. Some acaricides have label claims of repellency, but the repellency characteristics should not be relied on for long-term tick control.

    Antifeeding prevents proper functioning of a tick’s mouthparts, thereby preventing the tick from attaching to a dog and feeding. Amitraz and fipronil are examples of antifeeding chemicals. Permethrin can also affect the functioning of a tick’s mouthparts.

    Flushing effect refers to the time after application of a product in which a tick leaves the host and dies. Effective tick prevention should not include products that mostly rely on the flushing effect.2 These products are not designed to prevent bites; they are designed to treat an infestation on the host. All common acaricides sold through veterinarians have a moderate to good flushing effect.

    Knockdown effect is the speed at which a chemical kills a tick. After a tick bites a host and begins feeding, it is thought to take over 24 hours to transmit most pathogens. When analyzing which tick preventive to use, veterinary professionals should consider the knockdown effect.

    Owner compliance and proper recommendations by veterinary staff are crucial for ensuring the safety and efficacy of products that are placed directly onto a dog. The veterinary staff should recommend that these products be used year-round and according to the product label.

    Frequent bathing may affect the efficacy of these products. Dermatologic shampoos are more likely than normal detergent shampoos to affect the efficacy of these products.2 If a dog is bathed frequently, other forms of tick control should be recommended to the client. Check the product label for directions on bathing a dog before and after application of the product and share this information with the client.

    Area-Wide Acaricides

    Area-wide acaricides provide tick control to a large area. These products generally need to be applied only once or twice a year, are relatively inexpensive, and are easy to apply. This type of intervention should focus on controlling the nymphal stage of ticks. Applying these products in May or early June and again in October can dramatically reduce the tick population in an area (i.e., up to a 90% reduction). When these products are applied, the focus should be on the perimeter of the tick-safe zone (see Habitat Modification below), wooded areas, stone walls, and ornamental plantings.

    Many of these products are for home use, while others are restricted for sale and use by a licensed pesticide professional. Before purchase, owners should ensure that the label indicates that the product is designed for area-wide tick control. Many of these products also harm mammals, aquatic animals, beneficial insects, or certain plants, so care should be taken to use the correct product. Over time, these chemicals may leach into ground water, which can affect well water safety and cause other environmental concerns.

    Area-wide acaricides are available in liquid and granular formulations. The liquid formulations have been shown to be more effective.3

    Veterinary personnel should become familiar with a few of these products so that they can make recommendations to clients and educate them about proper use.

    The Organic Farming Association has set standards for controlling ticks in organic yards and gardens. Products that can be used in organic yards and gardens include products that contain insecticidal soaps or botanical insecticides. These products cannot be formulated with EPA List 1 inert ingredients. For more information on the use of pesticides in organic farming, visit USDA Agricultural Marketing Service and Organic Consumers Association.

    Biologic Control

    Biologic control is a newer approach to controlling ticks in the environment. Pathogenic fungi have been shown to control tick populations.3 Several species of fungi, such as Beauveria bassiana and Metarhizium anisopliae, can be used. These fungi occur naturally and are nontoxic to mammals. They work by infecting ticks when fungal conidia attach to the cuticle of the tick’s outer body surface. The fungi then germinate and penetrate the cuticle, and hyphae grow, causing a fungal infection that kills the tick. M. anisopliae also produces secondary metabolites that are toxic to ticks. These products work on other arthropods but do not generally affect beneficial insects, such as honeybees, when used properly. Several products are in development, and a few that can be used in residential settings are available.

    For many years, people have used guinea fowl or turkeys to help control tick populations. It is thought that these birds eat ticks, which controls the population. Birds have not been proven to effectively control ticks and, therefore, should not be used as the primary method of controlling ticks. Other biologic methods, such as the use of parasitic nematodes and wasps, have proven ineffective because of climate changes and the life cycles of ticks and wasps.

    Habitat Modification

    The goal of habitat modification is to control the number of ticks—not to completely eliminate them—in an area where a dog is allowed to roam. Ticks primarily live in densely wooded areas, particularly in low-lying brush and plants. Ticks can also be found in grass and in ornamental vegetation. In residential lawns, 82% of ticks are found within 3 yards of the lawn perimeter.3 Basic habitat modifications include keeping the lawn trimmed, removing leaves or other debris that accumulates, and reducing groundcover.

    An area should be designated a tick-safe zone, meaning that it should be unattractive to ticks and, therefore, should have a decreased tick population. For example, ticks prefer dark and humid areas, so creating an area with direct sunlight by cutting tree branches can be effective. The humidity of an area can be decreased by planting grasses and plants that do not require a lot of watering.

    A border area that is approximately 3 yards in width should be created around the tick-safe zone. This border area should have few or no low-lying plants and be covered with woodchips or other landscaping material. Dog houses and outdoor pet beds should be placed within the tick-safe zone. Creating and maintaining a border area has been shown to reduce the tick population by 72% to 100% within a tick-safe zone.3

    Host Manipulation

    Owners should be encouraged to check their dogs for ticks every day and instructed about proper tick removal (BOX 1) .

    Daily removal of ticks can greatly reduce the chance that a dog will acquire a disease. Long-haired dogs may need to be clipped in the summer to allow easier tick identification and removal. Dogs without proper tick protection should have limited access to wooded or forested areas.

    Ticks feed on almost all vertebrates, so any animal that comes into contact with a residential lawn could spread ticks. Controlling contact with wildlife is paramount to controlling the tick population. The control of wildlife should focus on controlling deer, small mammals/rodents, and birds.

    Many owners enjoy seeing deer in their neighborhoods; however, in areas that have a significant deer population, it is estimated that more than 90% of adult ticks feed on deer.3 Each tick can lay thousands of eggs each year. Deer can be managed with deer fencing, repellents, and deer-resistant landscaping.

    Deer fencing is the most effective method for controlling deer. In the Northeast, placing a deer fence around a large area has been shown to decrease the nymph population by 84% and the larval tick population by 100%.3 Although deer can leap 8 ft into the air from a standing position, they are more likely to try to push under obstacles such as fences. A deer fence should be 5 to 6 ft tall and secured to the ground. Many different materials, such as chain link, wood, polypropylene plastic, or steel mesh, can be used for deer fencing.

    Deer repellents can be effective when used in areas with low deer populations. Repellents act as deterrents to help reduce damage to plants and gardens; deer do not typically forage on lawns. The performance of repellants varies greatly depending on the product, application, rainfall, and the availability of other food sources for deer.

    It has been suggested that using landscaping to make a yard unattractive to deer can cause ticks to go elsewhere for food, but this has not been proven to be completely effective, perhaps because many plants that are not attractive to deer are attractive to ticks. The goal of the landscaping method is to design a landscape that is not palatable to deer. To do this, an extensive knowledge of plants is needed.

    Small mammals and rodents are important reservoirs of tick-borne pathogens. Mice are the most abundant and efficient animal reservoir for Borrelia burgdorferi, Babesia spp, and Anaplasma spp. In a study conducted in the Northeast, more than 90% of mice were found to carry B. burgdorferi, and 50% were shown to carry all three pathogens.3

    Other small mammals that carry ticks include voles, shrews, prairie dogs, chipmunks, and squirrels. Although not a significant risk, birds can also bring ticks onto a property. Keeping these animals away from a lawn can be more challenging than keeping deer away.

    Conclusion

    The best way to control tick-borne disease in dogs is to control the tick population. Not every method mentioned above is necessary to decrease the population, but a combination is recommended in areas with large tick populations. Veterinary professionals must educate clients about proper tick control and help them to make a personalized plan to control ticks.

    1. Romich JA. Tick-borne bacterial zoonoses. In: Understanding Zoonotic Diseases. Clifton Park, NY: Thomson Delmar; 2008:239-297.

    2. Blagburn BL. Tick control and vector borne diseases: what you need to know. Proc NAVC 2007.

    3. Stafford KC. Tick Management Handbook. New Haven, CT: The Connecticut Agricultural Experiment Station; 2007.

    References »

    NEXT: Tech Tips (March 2011)

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