Medically important ixodid ticks often carry multiple pathogens, with individual ticks frequently coinfected and capable of transmitting multiple infections to hosts, including humans. Acquisition of multiple zoonotic pathogens by immature blacklegged ticks (Ixodes scapularis) is facilitated when they feed on small mammals, which are the most competent reservoir hosts for Anaplasma phagocytophilum (which causes anaplasmosis in humans), Babesia microti (babesiosis) and Borrelia burgdorferi (Lyme disease). Here, we used data from a large-scale, long-term experiment to ask whether patterns of single and multiple infections in questing nymphal I. scapularis ticks from residential neighbourhoods differed from those predicted by independent assortment of pathogens, and whether patterns of coinfection were affected by residential application of commercial acaricidal products. Quantitative polymerase chain reaction was used for pathogen detection in multiplex reactions. In control neighbourhoods and those treated with a fungus-based biopesticide deployed against host-seeking ticks (Met52), ticks having only single infections of either B. microti or B. burgdorferi were significantly less common than expected, whereas coinfections with these 2 pathogens were significantly more common. However, use of tick control system bait boxes, which kill ticks attempting to feed on small mammals, eliminated the bias towards coinfection. Although aimed at reducing the abundance of host-seeking ticks, control methods directed at ticks attached to small mammals may influence human exposure to coinfected ticks and the probability of exposure to multiple tick-borne infections.

This review addresses the role of compounds secreted into the external environment that mediate important aspects of tick behaviour. Known as semiochemicals, these information-containing compounds include pheromones (used for conspecific communication), allomones (defence secretions) and kairomones (used for host identification and location). An impressive body of knowledge has accumulated concerning the identification of the compounds that comprise these semiochemicals. Pheromones are the best known and intensively studied, including arrestment (=assembly) pheromones, attraction–aggregation–attachment (AAA) pheromones and sex pheromones. Arrestment behaviour is mediated by contact with excreta from other ticks. In contrast, aggregating and sexual behaviours comprise a hierarchy of responses to different types of chemical compounds that must be recognized in a sequential order to achieve the end result. Ixodid ticks also produce an allomone that protects against certain insect predators. Finally, ticks use kairomones for host identification, e.g. volatiles such as CO2 and NH3 and various oils such as glandular secretions from deer. Knowledge of tick pheromones has been used to develop innovative new technologies for tick control. These products incorporate tick pheromones and small amounts of pesticide to attract and kill ticks on their hosts or in vegetation. The kairomones and the tick allomone also may be of interest for use in controlling ticks.

In Kenya, there are at least seven distinct tick-borne diseases (the ileriosis, anaplasmosis, babesiosis, heartwater, Nairobi sheep disease, sweating sickness and erhlichiosis in dogs). Theileriosis causes major economic losses arising from deaths of infected cattle.

Control of these diseases is almost exclusively by the application of chemical acaricides to cattle. Use of acaricides is regulated and only those passing field tests are permitted to be marketed in Kenya. Field trials on immunization against East Coast fever (ECF) by infection and treatment are still continuing. Chemotherapy treatment is also available but quite expensive.

The Veterinary Department continuously evaluates acaricides which have been documented to have activity against ticks. These acaricides have been grouped into four groups ranging from organophosphorus compounds in Group I to synthetic pyrethroids in Group IV. To-date Groups III and IV acaricides are kept as reserve, although amitraz in Group III can be used on a limited scale on privately owned farms.

Boophilus microplus is Brazil's outstanding livestock ectoparasitic pest (annual losses, US$ 1B), affecting, to varying extents, all its States, with a national herd of some 130 M cattle. The country's 8.5 M sq km and 23,000 km of land frontier with 10 tick infested countries complicate any concepts of national campaigns. Whereas Brazil is increasingly climatically suitable for B. microplus from south (three generations annually) to central (four) to north (potentially up to five), direct problems caused are incidentally decreased due to greater use of Bos indicus cattle at lower stocking rates; five tick population survival mechanisms are suggested. Voluntary, empirical chemical tick control remains the tradition, with little government involvement. Formamidine and synthetic pyrethroid acaricides dominate the market, due to former tick resistance to arsenicals, organochlorines and organophosphates, and market forces. Plunge dips, various sprayers, and “pour-on” formulations are used; first suspicions of tick resistance to synthetic pyrethroids have been reported. Various ecologically based “improved” tick control schemes produced promising results experimentally, but require a complementary vaccine against babesiosis/anaplasmosis before wide recommendation. Intensive use of synthetic pyrethroid acaricides has created tick-borne diseases and heightened demand for a live, frozen “vaccine”, in its pre-commercialization phase in Brazil. A strategic research and development approach has been adopted for widespread improvement to cattle ticks and tick-borne disease control in Brazil.

A situation report on the Ixodoidea infesting livestock in India is presented. Of the nearly 120 tick species known from this country, information regarding the hosts and distribution of 46 ixodid species belonging to eight genera and six argasid species belonging to three genera, parasitizing livestock has been provided. The ecology and disease relationship of the economically more important species have been reviewed. Notwithstanding the rich tick fauna, the native cattle seldom carry excessive tick burdens. Control is greatly facilitated by the high degree of natural resistance possessed by indigenous cattle, zebu. Chemical acaricides are the maincomponent of control strategies which are largely aimed at protecting the at-risk exotic and crossbred animals from ticks and the diseases transmitted by them. Exploitation of immunity and possibly some biological control may be integrated with the use of chemicals in future.

Risk-benefit considerations have stimulated efforts to develop technology to overcome the limitations of procedures that place excessive reliance on the use of acaricides for the control of ticks affecting cattle. One of the alternatives to acaricides is the selection and use of breeds of cattle with a natural propensity for developing acquired resistance to ticks. The literature on aspects of the modes of expression and mechanisms of resistance of cattle to ticks, is reviewed along with information on the successful efforts in Australia to develop productive Bos indicus ï Bos taurus breeds with the ability to develop high levels of resistance. The use of cattle resistant to ticks is discussed in relation to other factors that should be considered in the design of a programme for tick control.

The systems analysis approach is an appropriate procedure for the effective development of a management model for the strategic control of ticks. The interacting nature of the controllable and uncontrollable factors, and the difficulty in mimicking such complex situations experimentally, should be considered in the formulation of such models. ICIPE's approach relies on the use of both deterministic and stochastic models, and assumes unambiguous definitions of management's expectations.

Increasing costs of tick control have necessitated a complete re-assessment of its economic impact. There are two main approaches to studies on production economics. Some researchers advocate a “systems approach” in which all production traits and their interactions are monitored simultaneously, whilst others claim that studies must produce specific data on selectively identified components in the system which can then be used in process/simulation type models.

Studies were carried out in Zambia using a farming systems approach to quantify the effects of tick control on traditionally managed Sanga cattle. It seems that this decision was justified, because it is evident from the results that the determinants of the effects of tick control are extremely complex.

Overall herd productivity, i.e. outputs of milk and weaner calf per livestock unit carrying capacity, was about 25% higher in a tick-free herd. However, the annual cost of control in 1988 at ZK286.26 per livestock unit was greater than the increase in value of the products at ZK175.48 per livestock unit carrying capacity.

From this study, the intensive tick control in this system is not justified in the absence of serious tickborne disease. However, the analysis of various interactions indicate that limited seasonal tick control of adults from November to April would be economically viable. Calves should not be treated until they are 3 months of age.