The past: Historical and socio-economic aspects
The present: Some recent research
The future: Integrated tick and TBD control
General discussion
Conclusions
Bibliography
R.G. Pegram, R.J. Tatchell, J.J. de Castro, H.G.B. Chizyuka, M.J. Creek, P.J. McCosker, M.C. Moran and G. Nigarura
The authors are all present or former staff members of FAO or their senior national counterparts. Much of the work reviewed for the preparation of this paper was supported through collaborative programmes between FAO and the Danish International Development Agency (DANIDA) end between FAO and the United Nations Development Programme (UNDP) and the governments of Burundi, Ethiopia, Kenya, Malawi, the Sudan, the United Republic of Tanzania, Uganda, Zambia and Zimbabwe.
Approximately 80 percent of the world's cattle population of 1281 million are at risk from ticks and tick-borne diseases (TBD). Over a decade ago McCosker (1979) estimated global costs of control and productivity losses to be some US$7000 million annually (=US$7/head/year). In Africa, with 186 million head of cattle, ticks and TBD are the most serious constraints to increased production. Weekly or twice-weekly applications of chemical acaricides are still a common form of control; however, immunization against TBD and the economics of control have recently been receiving increasing attention. In this paper, aspects of the past, present and future of tick control are reviewed. The history of tick and TBD control from its inception until 1980 is reviewed and some of the research carried out during the 1980s is considered. Finally, future prospects for the adoption of revised tick control policies with particular emphasis on Africa are examined. Some recent research findings and their relevance to future control strategies are also discussed.
The practice of intensive tick control spread rapidly throughout Africa following the introduction of exotic cattle breeds. In many African countries it was enforced through legislation. In the past decade, however, it has become apparent that intensive tick control is prohibitively expensive; it must be emphasized that the cost-benefit of intensive tick control programmes has rarely been established since they have been based on the assumption that indigenous livestock requires the same degree of control as exotic stock. The consequence of this assumption is that, for nearly 100 years, millions of resistant cattle have been dipped regularly for the sake of a small proportion of susceptible exotic stock, leading to the loss of both resistance to ticks and enzootic stability to TBD.
The formulation of tick control strategies must be based on sound ecological data and economic assessments derived from studies on the impact of tick control or from experimental or field assessments of damage caused by ticks in the absence of control. National and individual perceptions of the need for tick control must also be understood by policy-makers.
Ecological studies
Ecological studies on ticks have been carried out in many countries in eastern and central Africa over the past ten years. They have concentrated on two ecological aspects: the effect of seasonal dynamics of ticks in parasitic phases on livestock and the development and survival of ticks during -free-living stages in pastures (Figure 1). Data derived from some of the studies have been integrated into computer population models and climate-matching models (Sutherst, 1987). For example, ecological data from Burundi were incorporated in computer simulations to estimate the number of ticks eliminated using different dipping strategies. The simulations were then used in the design of control strategies.
Economic studies
There are two scientific approaches to evaluating production losses caused by ticks. Sutherst (1987) suggests using simulation/process-type models for which specific single variables are investigated to determine damage coefficients, i.e. losses in live-weight gain (LWG) or of milk per tick (Table 1). Alternatively, a systems approach (on-farm study) has been advocated to assess the economic impact of ticks (Ellis, 1986; Pegram and Chizyuka, 1987). The importance of the faithful replication of field conditions in the design of productivity experiments was emphasized by Morris and Meek (1980). Similarly, in discussing the impact of trematodes on production, Dargie (1986) stated that "...the search for economically sound levels and means of control requires adequate measurements of the whole production process and not merely one component of it". Both approaches have been used in recent studies to quantify the economic impact of ticks and their control in Africa.
In southern Africa, Taylor and Plumb (1981), using fully tick-susceptible cattle, demonstrated a large difference (48 kg) in group mean-weight gain between heavily tick-infested and tick-free animals. Field trials in Kenya using Boran heifers immunized against East Coast fever (ECF) showed that animals dipped weekly gained an average of 78 g per day more than unclipped animals over a 30-week period (de Castro et al., 1985a). De Castro (1987) also demonstrated that high tick numbers caused proportionally greater live-weight losses in tick-susceptible Boran cattle than in tick-resistant animals of the same breed. Other trials have indicated that differences in LWG between tick-free and tick-infested animals are much smaller or negligible (de Castro et al., 1985b; Tatchell et al., 1986; Tatchell, 1988) (Table 2).
In Zambia, long-term studies using a farming systems approach were undertaken to quantify the impact of tick control on local Sanga cattle. In the first trial significant decreases in LWG occurred only in periods of medium to high challenge with adult Amblyomma variegatum (Pegram et al., 1989a and 1989b). In the second trial the impact of tick control on overall herd productivity was measured. Outputs of milk and weaner calf in relation to the carrying capacity of available land were found to be about 25 percent higher in a tick-free herd. The annual cost of control in 1988 at K286.26 (Zambian kwacha) for each livestock unit was greater than the increase in value of the products at K175.48 per livestock unit carrying capacity (Pegram et al., 1991) (Table 3).
A series of experimental studies were carried out in Zimbabwe [reviewed by Norval (1990)] to quantify the effects of feeding standard females of the species A. hebraeum and Rhipicephalus appendiculatus on meat and milk production for use as damage coefficients in computer simulation models. The reduction in LWG caused by each adult female tick completing its feeding was approximately 4 g for R. appendiculatus and 10 g for A. hebraeum. Losses in milk production caused by both species amounted to approximately 7 g for every female that became engorged.
Integrated tick management
Adequate scientific knowledge currently exists to support changes in the philosophy behind tick control. The general principles on which future strategies should be based were summarized by Tatchell (1986 and 1987) as follows:
· preserve enzootic stability or re-establish it through immunization against TBD;· educate farmers and advisers to accept the benefits gained from both boosting immunity to TBD and achieving host resistance to ticks that would result from relaxed tick control regimens;
· assess true benefits of using different cattle breeds;
· modify animal husbandry, for example, by allowing the more susceptible cattle to be grazed and treated together;
· institute tick control regimens based on sound economic thresholds.
Recently Tatchell (1992) further developed the concept of integrated tick management (ITM), emphasizing the importance of animal management, ecology, epizootiology and economics and marketing in the formulation of integrated policies for tick and TBD control. Essential elements of an integrated tick and TBD control programme include:
· appropriate legislation;· correct extension messages, for both disease and vector control;
· enzootic stability to TBD through immunization;
· host resistance to ticks using the correct breed, whether exotic or cross-bred dairy cattle or selected indigenous beef cattle;
· appropriate strategies, such as minimal control in periods of low challenge and strategic control for seasonal challenges;
· economics and marketing, considering the costs of vaccine production and delivery, the type of farming system, whether dairy or beef, and whether it is a private or public programme.
Novel methods in tick control
Major advances have been made in the development of novel methods and strategies for the control of ticks in recent years. New and easier methods of applying acaricides are available - ear tags, neck bands, tail bands and pour-one, for example - particularly for the pyrethroids with long residual activity. A mechanical applicator has also been developed (Duncan, 1991). In Kenya, an intraruminal ivermectin slow-release device providing 90-day protection against tick damage was demonstrated (Tatchell, 1992).
Tick repellents to use on livestock are limited (Mwase, Pegram and Mathers, 1990); however, several studies have indicated the potential benefits of using tick-repellent grasses and plants such as Melinis minutiflora, Stylosanthes species and Cassia absus. The application of tick attractants, such as pheromones, in combination with toxicants has also been considered. Pasture management, including spelling, has been used in Australia, and seasonal changes in cattle-grazing areas in Zambia are believed to be responsible for a decrease in tick numbers.
Tick control strategies
Specific strategies for the future vary according to the breed and type of cattle and to the management system. The following three main options are considered, with particular emphasis on strategic or minimal control regimens in which enzootic stability to TBD is established and maintained through natural exposure or, where necessary, through immunization.
Intensive dipping/spraying. Highly productive, pure-bred Bos taurus dairy cattle are likely to continue to require intensive tick control even though they represent only a small, specialized sector of the livestock industry and their suitability for many situations in Africa has been questioned.
Strategic tick control. In most farming situations using cross-bred (B. taurus x B. indicus) beef cattle, as well as in developing smallholder dairy systems that also use cross-bred cattle, strategic tick control would appear to be ecologically and economically feasible. These categories form the primary target for immunization programmes. The duration and frequency of treatment will vary according to the ecoclimatic zone and tick challenge (both in terms of numbers and species), the breed and type of animal, the relative costs of control measures and the value of animal products. Assessments will have to be made initially from available field and experimental data for tick damage and productivity and then verified under local conditions. Computer modelling may assist in these assessments. Annual or periodic adjustments need to be made based on prevailing costs. Where immunization is practiced, its costs should be included in the initial analyses.
1. Estimates of damage coefficients (live-weight-gain and milk losses) per engorged female - Estimation des dégâts (gain pondéral et rendement laitier) par femelle engorgée - Estimación del coeficiente de daños por hembra repleta (ganancia de peso vivo y pérdidas de leche)
|
Tick species |
Live-weight-gain loss (g) |
Milk loss (g) |
|
Amblyomma hebraeum (Norval et al., 1989) |
10 |
7 |
|
Amblyomma variegatum (Pegram & Oosterwijk, 1990) |
45-60* |
- |
|
Amblyomma americanum (Barnard, 1985) |
16-29 |
- |
|
Amblyomma maculatum (Williams, Hair & McNew, 1978) |
33 |
- |
|
Boophilus microplus (Sutherst et al., 1988) |
0.6-1.5 |
- |
|
Rhipicephalus appendiculatus (Norval et al., 1988) |
4 |
7 |
|
Rhipicephalus appendiculatus (de Castro et al., 1985b) |
NSD |
- |
NSD = non-sufficient data.
* Excluding compensatory live-weight gain.
2. Estimates of live-weight-gain losses in tick infested cattle - Estimation de la baisse de gain pondéral dans les troupeaux infestés par les tiques - Estimación de la disminución del peso vivo en los vacunos infestados de garrapatas
|
Place |
Author |
Duration of study |
Live-weight - gain loss |
Daily live-weight-gain loss |
|
Sudan |
Tatchell, 1988 |
4 |
1.6 |
13 |
|
Kenya |
de Castro et al., 1985b |
7 |
17 |
78 |
|
Kenya |
Tatchell et al., 1986 |
16 |
NSD |
NSD |
|
South Africa |
Taylor & Plumb, 1981 |
12 |
48 |
132 |
|
Zambia |
Pegram & Chizyuka, 19902 |
24 |
12 |
17 |
|
|
|
36 |
12 |
12 |
|
Zambia |
Pegram & Chizyuka, 1990 |
36 |
-Calf |
41 |
|
|
|
|
-Milk |
440 |
NSD = non-sufficient data.
1 Difference: tick- free > tick-infested.
2 5-10 kg over 3 to 4-month periods: compensatory live-weight gain + adverse effects of acaricide.
3. Estimates of productivity in tick-free and tick-infested herds - Estimation de la productivité dans des troupeaux exempts de tiques et dans des troupeaux infestés - Estimación de la productividad en hatos sin garrapatas y en hatos infestados
|
Category |
|
Tick-free herd |
Tick-infested herd |
|
Mature age |
- cows [at first calving] |
3.9 |
4.2 |
|
|
- calves [at weaning] |
204 |
238 |
|
Weight |
- cows [adult] |
221 |
215 |
|
|
- calves [at weaning] |
65 |
61 |
|
Mortality |
- cows |
4 |
5 |
|
|
- calves |
13 |
19 |
|
Milk |
- offtake |
83 |
69 |
|
|
- daily milk yield |
2.4 |
2,0 |
|
Calving interval |
|
511 |
591 |
|
Cattle production efficiency factor |
- offtake |
903 (+24%) |
727 |
K = Zambian kwacha.
Lucc = livestock unit carrying capacity.
Control benefit K176 - control cost K286 = - K110 per livestock unit.
4. Daily live-weight gain and mean adult tick counts of Amblyomma variegatum and Rhipicephalus appendiculatus in different cattle breeds1 - Gain pondéral journalier et nombre moyen de tiques adultes (Amblyomma variegatum et Rhipicephalus appendiculatus) recensés sur différentes races de bovins - Aumento diario de peso vivo y número medio de garrapatas adultas de las especies Amblyomma variegatum y Rhipicephalus appendiculatus en distintas razas de vacunos
|
Breed/group |
Daily live-weight gain (g) |
A. variegatum |
R. appendiculatus |
|
Ankole (treated) |
185 |
- |
- |
|
Ankole (untreated) |
199 |
25 |
32 |
|
Sahiwal x Ankole (treated) |
216 |
- |
- |
|
Sahiwal x Ankole (untreated) |
185 |
18 |
37 |
|
Friesian x Ankole (untreated) |
204 |
25 |
62 |
|
Brown Swiss x Ankole (untreated) |
161 |
21 |
50 |
|
Guernsey x Ankole (untreated) |
247 |
24 |
101 |
1 See Figure 2.
Minimal or threshold tick control. Various studies have demonstrated that, in situations where tick control has been decreased or stopped completely, enzootic stability is re-established and maintained with no subsequent increase in the prevalence of TBD. Therefore, under conditions of enzootic stability, whether induced or occurring naturally, the implementation of minimal tick control may be justified. When Amblyomma species are abundant, spraying the preferred sites of adult ticks will reduce udder damage. At times of very heavy tick challenge, systems such as slow-release ivermectin boluses or implants may help to control damage while maintaining enzootic stability.
Marketing and management
A major conclusion reached at the Conference on Improving Agricultural Production in Africa, which was held in Abidjan, Côte d'Ivoire, in 1992, was that marketing is a prime constraint on the improvement of livestock productivity. Therefore, viable markets must be developed in many countries for surplus production resulting from any improvements in livestock productivity.
The importance of animal management, particularly nutrition and breed selection, in any viable livestock industry must be emphasized. While beef may be produced efficiently by local breeds, milk production requires cross-bred animals. However, it is rarely appreciated that the quantum leap apparent in milk production with B. taurus breeds is only possible with an equivalent leap in management. Ideally, the use of other more adaptable breeds should be considered. In tropical and subtropical Australia, the integrated pest management (IPM) approach to tick control is now being applied to the dairy industry with the development of adapted and more resistant crossbreeds such as the Australian Friesian-Sahiwal (AFS) and the Australian Milking Zebu (AMZ). In Kenya, the International Livestock Centre for Africa (ILCA) has demonstrated the suitability of Ayrshire-Sahiwal crosses. The Sahiwal breed is said to exhibit a high degree of resistance to ticks. Studies in Burundi confirmed this, but they also showed that a group of Sahiwal x Ankole crosses kept tick-free had better LWG than a similar tick-infested group. However, it was a group of susceptible, heavily tick-infested Guernsey x Ankole crosses that had the highest LWG (Table 4 and Figure 2).
Local breeds such as Boran, Kenana and Mashona should also be considered for immediate use or for selective improvement.
Ecological factors
Recently, the importance of temperature and diapause in the phenology of R. appendiculatus has been demonstrated (Berkvens, Pegram and Brandt, 1992). An eastern African strain of R. appendiculatus exhibited diapause when exposed to field conditions in Zambia. This brings into question the recent hypothesis of Norval et al. (1991) that non-diapausing populations of R. appendiculatus, which were assumed to have been introduced in cattle with ECF from eastern Africa, were associated with the continued presence of ECF in southern Africa. At certain localities in eastern Zambia, however, temperatures are sufficiently high in some years to allow early cohorts of local populations of R. appendiculatus to develop rapidly enough to facilitate a second generation of adults in the May-June period. It is suggested that if the phenomenon of global warming leads to temperature increases of 2° to 3°C in central Africa, then second generations may occur throughout much more of the region. This could have serious implications for seasonal tick control strategies.
Host resistance
It is known that in many subtropical and semi-arid environments in Africa indigenous dual-purpose breeds are highly resistant to ticks, resulting in low infestation rates that cause insignificant direct losses. Massive losses caused by ticks and TBD occur in susceptible breeds of cattle if unprotected. Moreover, local indigenous cattle kept completely tick-free become equally susceptible. Any disruption of intensive control regimens can have disastrous effects, as was seen in Zimbabwe during the liberation war when the breakdown of dipping caused losses from TBD approaching one million head of cattle (Norval et al., 1991).
The phenomena of host resistance to ticks and enzootic stability to TBD are well documented (Perry et al., 1985; Tatchell, 1986 and 1987; Latif and Pegram, 1992). For example, in Africa east of the Great Rift Valley, the tick species R. pulchellus feeds heavily on large wild mammals, however, overall population densities are usually limited by host resistance. In cattle, resistance levels may vary greatly between breeds and between animals. For local Sanga cattle in Zambia, cumulative total counts of adult A. variegatum over a three-month period ranged from 128 to 1182. In contrast, it was demonstrated in Burundi that various cross-breeds showed marked differences in susceptibility to R. appendiculatus but not to A. variegatum.. Experimental observations on cattle have shown that less than 1 percent of ticks feed successfully on indigenous, resistant B. indicus breeds, whereas more than 50 percent may feed to repletion on exotic, susceptible B. taurus breeds. As noted earlier, although Sahiwal crosses exhibit a high level of resistance to ticks, they appear to respond significantly to control measures. It is therefore suggested that, while some breeds show high levels of resistance to ticks, it may be at the expense of productivity.
Tick damage and tick/host interactions
Damage coefficients for each engorged standard female can be used in simulation models to estimate production losses caused by ticks and the economic benefits of control strategies. To date, however, these data have not been verified through long-term field trials, and there is some evidence that reduction in weight gain and milk production attributed to ticks under natural field conditions may not show simple linear relationships (Barnard, 1985; Stachurski, Barre and Camus, 1988; Pegram et al., 1991). This would be in general agreement with the statement of Hawkins and Morris (1978) that "...each additional parasite has less effect than the one before it...". A review of the data from field trials carried out to assess the impact of tick control emphasizes that the effects of tick infestations show considerable variation. Several reasons for this were highlighted, including: the differences in susceptibility or resistance of the hosts, which also influence grooming and grazing behaviour; the differences in quality and quantity of available grazing, which are related to seasonal effects; the timing and abundance of sequential tick burdens; and the timing of possible periods of compensatory weight gain.
In the comprehensive field trials conducted in Zambia, the overall effects of tick control were influenced by several often-complex interactions:
· treatment- season-calf LWG-tick abundance
· treatment-milk availability-calf age-calf LWG
· calf LWG-weaning age and weight-calving interval
· calving interval-calving season-parity II milk yields
· treatment-calf age-mortality.
The effects of these major interactions are considered briefly. More than 90 percent of the overall improvement in milk yields occurred between November and April. Greater milk yields enhanced calf growth, which reduced the time up to weaning and, subsequently, the calving interval. This in turn led to a change in the calving season of alternate parturitions so that cows calved in October-November, coinciding with improved nutrition and, consequently, much greater milk yields. However, there was a direct negative effect from treating calves of less than three months of age. It was also shown that the conversion index (daily LWG of calves/daily milk intake) was greater in treated herds. Thus, tick-free cows produced higher quality milk than tick-infested cows, or calves of tick-free dams converted each unit volume of milk to meat more efficiently than calves of tick-infested dams (Figure 3)
The relationships between tick numbers and host nutrition are also complex. It has been shown in Australia that two-thirds to three-quarters of the adverse effect of Boophilus microplus ticks on growth rates is the result of a decrease in appetite (Seebeck, Springell and O'Kelly, 1971; Nelson, 1984). This may be true of most tick species. It is suggested, therefore, that when host metabolism is diminished during periods of reduced feed availability, the adverse anorectic effect caused by ticks may be less. This hypothesis is supported by observations made in several countries with different tick species. In Australia, Sutherst et al. (1983) reported smaller losses in LWG per engorging female of B. microplus in autumn and winter (0.47 g/tick), when cattle grow more slowly (90 g/day) or lose weight (-120 g/day), than in summer (0.72-1.52 g/tick), when cattle grow more quickly (310-590 g/day)
Extrapolation of results from experimental studies with A. hebraeum and R. appendiculatus in Zimbabwe (Norval et al., 1988 and 1989) indicate a similar phenomenon. The authors estimated the effect of each standard female of A. hebraeum on LWG to be 9 to 19 g during the first 35 days, when cattle gained weight at approximately 280 g/day. In the third period of 35 days, when cattle gained only 86 to 114 g/day, the estimated effect of each female was 1 to 3 g. In the experiments with R. appendiculatus, the loss per standard female was estimated at 6 to 8 g during the first 28-day period, when Nkoni cattle gained 800 g/day and Friesian x Hereford (FH) crosses gained 200 to 446 g/day. In contrast, in the third 28-day period, when Nkoni cattle were gaining only 18 to 32 g/day and the FH crosses were losing weight, the loss per female was 3 to 4 g/day. In a study with quasi-natural infestations of A. variegatum in Zambia, grazing was poor and growth rates were low during the first eight weeks in both tick-free (151 g/day) and tick-infested (146 g/day) cattle. When overall growth rates were higher, the tick-free animals gained significantly more weight (468 g/day) than heavily tick-infested animals (385 g/day) (Pegram and Oosterwijk, 1990) (Figure 4).
The authors concluded from these observations that relationships between tick numbers and losses in weight gain are unlikely to be linear and may vary considerably in different situations depending on several factors such as host nutrition, breed, season and host resistance. If, as mentioned above, two-thirds to three-quarters of the adverse effect of ticks is caused by appetite depression, then one would expect that a threshold number of ticks may cause maximal anorexia. Each additional feeding tick would have a much lower influence on weight loss because of its specific effect. These complex interactions have been emphasized to illustrate the point that the answer to tick control is far from simple! They should, therefore, be considered in the formulation of models on which tick control policies are to be based.
Economic aspects
Several authorities have questioned the justification for intensive tick control. Matthysse (1954) recommended that "...any large-scale tick control programme be preceded by an extended survey of seasonal tick populations, incidence of tick-borne disease, mortality and economic loss". Some 30 years later, Tatchell (1984) noted that "...countries lacking large-scale intensive tick control were keen to establish it whereas those where it was already practiced were trying to find ways of stopping it".
The only economic analyses available prior to the late 1980s were those of Ferguson (1971) and Sere (1979). Ferguson concluded that, in Uganda, "...control measures may provide the cornerstone for expansion of beef and milk production". At that time, however, control costs were much lower than they were in the 1980s: Pegram and Chizyuka (1990) noted that treatment costs in Zambia increased up to 52 times from the early 1950s to the late 1980s. It was concluded from the studies undertaken in Zambia that intensive tick control in the traditional, multipurpose livestock system is not justified in the absence of losses from TBD (Pegram et al., 1991). Strategic seasonal control of adult ticks every two weeks from November to April was suggested as an economically viable solution.
3. Interaction of the main effects of tick control on herd productivity and the subsequent change in calving season - Incidence des principaux effets de la lutte contre les tiques sur la productivité du troupeau et déplacement de la saison de vêlage - Interacción entre los principales efectos de la lucha contra las garrapatas sobre la productividad del hato y el cambio de la temporada del parto
4. Interaction of the main effects of tick infestation on live-weight gain and the possible influence of nutrition and the metabolic state of hosts - Incidence des principaux effets de l'infestation par les tiques sur le gain pondéral et influence possible de la nutrition et de l'état métabolique des hôtes - Interacción entre los principales efectos de la infestación de garrapatas sobre la ganancia de peso vivo, e influencia de la nutrición y estado metabólico del huésped
In addition to assessments of production losses related to ticks, an overall view of the economics of control and losses at the national level is essential. This is necessary because a particular site of an experimental or farm trial does not necessarily reflect the overall distribution of ticks and associated losses. For example, the damage to cattle caused by ticks is greatly exacerbated in areas where the incidence of secondary screwworm strike is high. Equally, while loss coefficients have been determined experimentally on growing animals, the more important type of loss is that found in breeding animals: ticks may be responsible for loss in udder quarters and may increase the calving interval. The latter is the most significant parameter in determining herd productivity and, hence, profitability. These types of losses are better estimated on a survey basis.
Government policy
The major issue facing policy-makers today is how much government should be involved in the delivery of veterinary services. This economic debate hinges on the extent to which the particular disease complex falls under the category of a "public" rather than a "private" good. For a long time tick control has been regarded as a national concern, hence the provision of communal dips by governments. However, where a country practices minimal dipping and maintains enzootic stability, tick or TBD control becomes the concern of individual producers. If farmers decide to operate intensive dairy farms with exotic cattle in an area with a high but enzootically stable ECF challenge, then they have to solve the problem for themselves. This requires that they receive correct information from extension services: they will need to know the cost and possible risks of each initiative, so that these may be weighed against the potential milk income as well as the capital value of the exotic dairy animal, plus any non-recurrent expenditures (dip construction, etc.), versus those of using a local breed. Looking at the current situation, where regulations for livestock movement are rarely enforced -if they are enforceable at all - and where cost recovery is the key to sustainable government activities, a change in integrated tick and TBD control policies may be overdue. Ways of increasing the farmer's choice must be considered, and this would require the minimal umbrella of government support to be redesigned.
Supported by ongoing research conducted during the 1980s, some countries have already initiated changes in tick control policies and practices. There are major constraints to immediate, widespread changes, however, including:
· Existing legislation in many countries that makes intensive tick control obligatory.· Political attitudes. In the past dip building often secured votes for local politicians who, for decades, accepted misinformation about the benefits of intensive tick control.
· Attitudes of scientists and radical changes in philosophy. In one country, an eminent researcher advocated the continuation of intensive dipping; however, within 12 months this researcher stated that costly, short-interval dipping was unnecessary.
· Attitudes of farmers. In some countries, dipping charges are now being levied as a result of policy changes. Farmers' perceptions of the benefits of intensive tick control were completely distorted by government subsidies, and they are now faced with full economic recovery for what they regard as a reduced and therefore less effective service.
· Inadequate professional and technical staff without the appropriate experience and adequate training in tick and TBD control.
Tatchell (1992) summed up the problem (pertaining to politicians, scientists and farmers) uniquely: "...lack of progress in the acceptance of ITM lies mainly in what van Emden (1989) calls 'user mentality' of preferring chemical control if it is effective because it is convenient and under their direct control". (Van Emden original reference not known to authors.)
Socio-economic perceptions
Burundi and Zambia have been most progressive in their revision of tick control policies. Several factors have contributed to their success. For example, in Burundi, the effectiveness of the widespread application of seasonal strategic tick control is largely a result of extension and training programmes (Moran and Nigarura, 1990). The current approach advocates weekly tick control applications over a four-month period that coincides with peak adult tick activity. Costs are kept to a minimum as the frequency of acaricide applications is decreased to one-third or one-sixth, dip tanks are emptied and recharged only once every four or five years and the level of the general dip tank management is high. Moreover, the policy decreases tick-resistance problems, environmental contamination and personnel costs.
Prior to the introduction of strategic dipping in Zambia, sociological implications were considered. A questionnaire designed to determine farmers' attitudes indicated that farmers perceived ticks as a major cause of wounds (56 percent), loss of condition (38 percent) and disease transmission (38 percent). They had good knowledge of the types (species) and seasonality of ticks and, consequently, the importance of dipping in the rainy season. Most farmers (91 percent) practiced tick control and were prepared to pay for it. Some were actually doing so at the time of the survey in 1984.
In adopting the revisions suggested, there are at least three important political, social and economic implications to be addressed. First, in the adoption of new policies, informed professional staff (both veterinarians and livestock economists) will need to convince politicians of the necessity of accelerating the revision of legislation to facilitate the changes. Second, extension services extended to participating farmers through auxiliary field staff will need to be given high priority. Finally, as farmers are increasingly expected to contribute to costs of control programmes, efforts to improve available markets for livestock products will be required.
The new technically efficient and easily administered forms of chemical tick control should be attractive to farmers since they would be under their direct control; however, commercial pressure will be necessary to encourage their use. Extra effort will be needed to emphasize the high cost and foreign exchange requirements of traditional tick control programmes and to highlight the potential for achieving equivalent benefits through the use of this more robust low-tech system using an acaricide with low residual activity to enhance the possibility of maintaining enzootic stability.
Collectively, politicians, animal health and production personnel and farmers themselves can contribute to stronger national and personal- prosperity.
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