Tick Control

Biological control measures can be directed against both the free-living and parasitic stages of ticks. The free-living stages of most tick species, both ixodid and argasid, require specific microclimates and are restricted to particular microhabitats within ecosystems inhabited by their hosts. Destruction of these microhabitats decreases the abundance of ticks.

Alteration of the environment by removing certain types of vegetation has been used to control Amblyomma americanum in recreational areas in the southeastern US and to control Ixodes rubicundus in South Africa.

Control of argasid ticks such as Argas persicus and A walkerae in poultry can be achieved by eliminating cracks in walls and perches, where free-living stages shelter.

The abundance of tick species can also be decreased by removing alternative hosts or hosts of a particular stage of the life cycle. This approach has occasionally been advocated for control of three-host ixodid ticks such as Rhipicephalusappendiculatus, Amblyomma hebraeum, and Ixodes rubicundus in Africa, and Hyalomma spp in southeastern Europe and Asia.

Rotation of pastures or pasture spelling has been used to control the one-host ixodid tick Rhipicephalus (subgen Boophilus) microplus in Australia. The method could also be applied to other one-host ticks, in which the duration of the spelling period is determined by the relatively short life span of the free-living larvae. However, it has minimal application to multihost ixodid ticks or argasid ticks because of the long survival periods of unfed nymphs and adults.

Predators, including birds, rodents, shrews, ants, and spiders, play a role in some areas in decreasing the numbers of free-living ticks. In the New World, fire ants (genus Solenopsis) are noteworthy tick predators. Engorged ticks may also become parasitized by the larvae of some wasps (Hymenoptera); however, these have not notably decreased tick populations.

Zebu (Bos indicus) and Sanga (a B taurus-B indicus crossbreed) cattle, the indigenous breeds of Asia and Africa, usually become very resistant to ixodid ticks after initial exposure. In contrast, European (B taurus) breeds usually remain fairly susceptible. The tick resistance of Zebu breeds and their crosses is being increasingly exploited as a means of control of the parasitic stages. The introduction of Zebu cattle to Australia has revolutionized R microplus control on that continent. Use of resistant cattle as a means of tick control is also becoming important in Africa and the Americas. In Africa, ixodid tick infestations on livestock and wild ungulates may also be decreased by oxpeckers (Buphagus spp), which are birds that feed on attached ticks.

Control of ticks with acaricides may be directed against the free-living stages in the environment or against the parasitic stages on hosts.

Control of ixodid ticks by acaricide treatment of vegetation is used in specific sites (eg, along trails) in recreational areas, in the US and elsewhere, to decrease the risk of tick attachment to humans. This method has not been recommended for wider use because of environmental pollution and the cost to treat large areas. Dog kennels, barns, and human dwellings may also require periodic treatment with acaricides to control the free-living stages of ixodid ticks such as Rhipicephalus sanguineus (the kennel tick).

The free-living stages of argasid ticks, which infest specific foci (eg, fowl runs, pigeon lofts, pigsties, and human dwellings), are more frequently and more effectively treated with acaricides.

Treatment of hosts with acaricides to kill attached larvae, nymphs, and adults of ixodid ticks and larvae of argasid ticks has been the most widely used control method. A variety of ectoparasiticide products are available on the market to treat animals against ticks. Some ectoparasiticides are applied as sprays, dips/washes, spot-on treatments, or impregnated ear and tail tags and collars and distributed cutaneously (on the skin surface). Other treatments are administered PO and distributed via systemic circulation. In general, ticks must attach to an animal and acquire a blood meal for blood-distributed ectoparasiticides to be effective. Alternatively, cutaneously distributed ectoparasiticides have potential to both kill attached ticks and prevent the attachment of new ones.

Pyrethroids, including fipronil, permethrin, and permethrin combination products, are effective ectoparasiticides because of rapid penetration of arthropod cuticle and high accumulation in arthropod tissues. However, topically applied cutaneous ectoparasiticides may not achieve uniform distribution, with some body parts not being covered to the same extent and concentration (eg, hindlimbs versus the back). This may be due to increased distance from the original application site as well as to greater comparative loss of active ingredient from the legs during routine life activities.

Pyrethroids are safe and effective in dogs; however, they are toxic to cats, rabbits, and fish and should be avoided in these species.

Systemically distributed ectoparasiticides, including afoxolaner, fluralaner, and sarolaner, tend to achieve more uniform distribution throughout the animal body and extremities but may take longer to reach full efficacy and have somewhat lower speed of kill.

See also Ectoparasiticides.

An advance of potentially great importance has been the production, using biotechnology, of a promising vaccine against R microplus. The immunizing agent is a concealed tick antigen not normally encountered by the host. The immune mechanism it stimulates is different from that stimulated by exposure to ticks (ie, tick feeding). The antigen was derived from a crude extract of partially engorged adult female ticks. It stimulates the production of an antibody that damages tick gut cells and kills the ticks or drastically decreases their reproductive potential.

Prospects for developing similar vaccines against other ixodid tick vectors of cattle diseases of major veterinary importance are not clear. Rhipicephalus ticks are good candidates for such vaccines, in that they are one-host ticks and show a marked preference for bovine hosts, which act as the principal reservoir of perhaps the most important group of disease agents (Babesia spp) these ticks transmit. By contrast, most other tick vector species of agents that cause important cattle diseases (eg, anaplasmosis, heartwater, theileriosis) are three-host ticks, which infest not only cattle but also wild ungulate species, for which vaccination is not feasible. Moreover, many wild ungulate hosts of the vector ticks serve as reservoirs of these disease agents. For these reasons, vaccines against nonboophilid vector ticks may be unable either to eradicate the ticks or to eliminate important sources of the disease agents they transmit.

Initially, the main uses of acaricides were for eradicating ticks, preventing spread of ticks and tickborne diseases (quarantine), and eradicating and controlling tickborne diseases.

Eradication programs were successful in some ecologically marginal subtropical areas, such as the southern US and central Argentina, where Rhipicephalus spp and babesiosis were eradicated, and southern Africa, where East Coast fever (caused by Theileria parva parva) was eradicated. The programs were less successful in the ecologically more favorable tropical areas of northeastern Australia, Central America, the Caribbean islands, and East Africa.

In areas where eradication was not achieved, costs of maintaining intensive tick control programs often have become prohibitive. For this reason, integrated biological and chemical control strategies are being adopted. The effectiveness of these cost-containment strategies requires better knowledge of the dynamic associations among the disease agents, their vertebrate hosts, the tick vectors, and the environment.

Strict quarantine measures to prevent reintroductions are enforced in countries from which ticks and tickborne diseases have been eradicated. Climate-matching models, geographic information systems, and expert systems (models based on expert knowledge and artificial intelligence) are being used to identify unaffected areas in which tick pests could become established if introduced.

Control of these diseases will require use of the principles of endemic stability and development of improved recombinant vaccines. A promising strategy is identifying receptor sites on the midgut of vector ticks and developing antibodies that bind with these sites, thereby blocking tick-ingested tickborne pathogens from infecting the tick. Cattle injected with receptor-site antigens may produce antibodies that feeding ticks ingest.

• Procedure for eradicating cattle tick from infested land. Department of Agriculture and Fisheries. Biosecurity Queensland. Biosecurity Acts 2014.

• Protecting US cattle from fever ticks. USDA Animal and Plant Inspection Service.

• Also see pet owner content regarding ticks of dogs, cats, and horses.