| The main reasons for tick control are to protect hosts from irritation and production losses, formation of lesions that can become secondarily infested, damage to hides and udders, toxicosis, paralysis, and of greatest importance, infection with a wide variety of disease agents. Control also prevents the spread of tick species and the diseases they transmit to unaffected areas, regions, or continents. |
| Cultural and Biologic Control: |
| These 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, have specific requirements in terms of microclimate and are restricted to particular microhabitats within the ecosystems inhabited by their hosts. Destruction of these microhabitats reduces the abundance of ticks. Alteration of the environment by removal of certain types of vegetation has been used in the control of
Amblyomma
americanum
in recreational areas in southeastern USA and in the control of
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, which provide shelter to the free-living stages. |
| The abundance of tick species can also be reduced by removal of alternate hosts or hosts of a particular stage of the life cycle. This approach has occasionally been advocated for the control of 3-host ixodid ticks such as
Rhipicephalus
appendiculatus
,
Amblyomma
hebraeum
and
Ixodes
rubicundus
in Africa, and
Hyalomma
spp
in southeastern Europe and Asia. |
| Rotation of pastures or pasture spelling has been used in the control of the 1-host ixodid tick
Boophilus
microplus
in Australia. The method could also be applied to other 1-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 the unfed nymphs and adults. |
| Predators, including birds, rodents, shrews, ants, and spiders, play a role in some areas in reducing the numbers of free-living ticks. In the New World, fire ants (
Pheidole
megacephala
) are noteworthy tick predators. Engorged ticks may also become parasitized by the larvae of some wasps (Hymenoptera), but these have not significantly reduced 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 the control of
B
microplus
on that continent. Use of resistant cattle as a means of tick control is also becoming important in Africa and the Americas. In Africa, infestations of ixodid ticks on livestock and wild ungulates may also be reduced by oxpeckers (
Buphagus
spp
), which are birds that feed on attached ticks. |
|  |
| Chemical Control: |
|
See also
ectoparasiticides, Ectoparasiticides . 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 has been done in specific sites (eg, along trails) in recreational areas in the USA and elsewhere, to reduce the risk of tick attachment to people. This method has not been recommended for wider use because of
environmental pollution and the cost of treatment of 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 the kennel tick,
Rhipicephalus
sanguineus
. |
| The free-living stages of argasid ticks, which infest specific foci such as fowl runs, pigeon lofts, pig sties, 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. In the first half of the century, the main acaricide was arsenic trioxide. Subsequently, organochlorines, organophosphates, carbamates, amidines, pyrethroids, and avermectins have been used in different parts of the world. The introduction of new compounds, such as the phenylpyrazoles, has been necessary because
of the development of resistance in tick populations. |
| Acaricides are most commonly applied to livestock by use of dips or sprays, with dips being considered the more effective. In recent years, several other means of acaricide application have been developed, including slow release of systemics from implants and boluses, slow release of conventional acaricides from impregnated ear tags, pour-ons (which are applied on the back and spread rapidly over the entire body surface), and spot-ons (which are similar but have less ability to
spread). On fowl, acaricides are usually applied as dusts; on cats as dusts or washes; and on dogs as dusts. |
| For many years, pyrethroids and organophosphates formulated as dusts, dips, or collars were used on dogs and cats to control ticks. With the advent of the phenylpyrazoles, long-lasting spray and convenient spot-on formulations were introduced. Recently, pyrethroids have been introduced as highly concentrated spot-on products that are labeled only for dogs due to their toxicity in cats. The use of these concentrated pyrethroids is not advised on dogs if a cat is even in the same household. |
| |
|
Vaccines: |
| A recent advance of potentially great importance has been the production, using biotechnology, of a promising vaccine against
B
microplus
. The immunizing agent is a concealed tick antigen, not normally encountered by the host. The immune mechanism that 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 reduces their reproductive potential. Prospects of developing similar
vaccines against other ixodid tick vectors of cattle diseases of major veterinary importance are not clear.
Boophilus
ticks are good candidates for such vaccines in that they are 1-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
) that
Boophilus
ticks transmit. By contrast, most other tick vector species of agents that cause important cattle diseases (eg, anaplasmosis, heartwater, theileriosis) are 3-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. |
| |
| Control Strategies: |
| Initially the main uses of acaricides were tick eradication, prevention of spread of ticks and tickborne diseases (quarantine), and eradication and control of tickborne diseases. The eradication programs were successful in some ecologically marginal subtropical areas, such as southern USA and central Argentina where
Boophilus
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 the areas where eradication was not achieved, the costs of maintaining intensive tick control programs often have become prohibitive. For this reason, integrated biologic 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 using the principles of endemic stability and developing improved recombinant vaccines. A current, promising strategy is the identification of receptor sites on the midgut of vector ticks, and the development of 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. |
| |
