The problems encountered with previous tsetse and trypanosomiasis control strategies are discussed. In an effort to ensures long-term sustainability of future programmes in a perhaps more difficult funding climate, there is currently an on-going reappraisal of tactics. The concerns of donors have encouraged a more analytical approach to the problem and are also helping to ensure that a much wider view is taken of trypanosomiasis control within rural development as a whole.
The options of localised eradications as opposed to long-term control are discussed. In view of the acute shortage of national funding for the foreseeable future, and the donors' reluctance to support open-ended, long-term recurrent control projects, attention is being focussed on possible community involvement to help ensure sustainability of any control measures: the possible limitations of this approach are discussed.
The various control/eradication techniques presently available are discussed as to their relative merits and drawbacks, especially with references to their potential for large-scale use and amenability for community participation. A fully analysed approach to the use of these various techniques should lead to a policy of using integrated techniques in any large-scale programme. Co-ordinated regional intervention programmes are to be encouraged as a more credible approach to the problem.
1. RECENT APPROACHES TO CONTROL
Over the last 30 years or so, policies for the control of animal trypanosomiasis have relied largely on the use of drugs and in certain situations, the use of insecticides in programmes to control or locally readicate the vector, the tsetse fly.
Control of trypanosomiasis through the use of drugs has been mainly by therapy: although prophylaxis has been used to protect livestock under low to medium challenge, it has usually been restricted to commercial enterprises where there is regular take-off and income generation. In the traditional livestock sector, there has rarely been sufficient income available to enable the owners to even consider regular prophylaxis. In general, the supply of drugs has often been intermittent, mainly through inadequate funding (where Government has been the supply intermediary) or lack of foreign exchange (for both Government and private sector supply). This has led to the mismanagement of the drugs concerned with the consequent development of resistant trypanosomes. This has been of particular concern because of the limited range of drugs available. Also the drugs have been applied often in a haphazard way, rarely following the regimes or dosage rates recommended.
In addition, because of a lack of equipment, reagents or qualified staff, little is attempted in the form of trypanosomiasis diagnosis and monitoring which are essential prerequisites to the effective planning and implementation of prophylactic and therapeutic regimes. The resultant lack of adequate information on trypanosomiasis distribution and incidence also greatly complicates the planning and economics justification of control campaigns.
However, in many countries, such drug reliance has, of necessity, been the basis of their trypanosomiasis controls, mainly due to inadequate funding precluding the introductions of any vector control measures. Certainly this has been the situation in most of West and East Africa.
In much of the humid and subhumid zones of Central and West Africa, there has been the exploitation of the N'Dama and West African Shorthorn trypanotolerant breeds of cattle. However, it has to be stressed that they are tolerant only and succumb to the disease under high challange or physiological stress.
Aggressive vector control, mainly through the use of insecticides, has been possible in some areas and countries, where Government funding has been available. This has often been as a response to deteriorating disease or expanding fly situations. Thus much of the tsetse control in Uganda has been to control Sleeping Sickness epidemics. In the subhumid and semi-arid parts of southern Africa, such vector operations were largely in response to a rapidly expanding flybelt situation. Following the rinderpest panzootic at the turn of the century, when wildlife populations were severely reduced and major fly recessions occurred in their overall distribution, there was substantial settlement of these newly ‘cleared’ areas by both commercial and traditional farmers. As the game and fly recovered, these areas steadily came under threat. Barriers were instituted to contain these advances and some attempts made to reverse this reinvasion, largely using ground and, in later years, aerial spraying.
However, the technical difficulties and expense associated with the construction and maintenance of the barriers which were not totally effective, and the advent of new control technologies, subsequently led to a reappraisal of tactics.
2. PAST EFFORTS AT SUSTAINABILITY OF PROGRAMMES
Until recently, most of the tsetse and trypanosomiasis control efforts were based on any particular Government's ability to self-finance such work. It also depended of course on the relative importance Governments paid to this problem, based on their appreciation of its constraints. The relative importance of the livestock industry to the economy and social structure of the country influenced funding levels, as obviously did any human Sleeping Sickness epidemics or threatening fly advances.
Zimbabwe, Zambia, Botswana, Nigeria, Cameroon and Uganda are perhaps the main countries which have been fortunate enough in the past to have had both the adequate resources and the responsive governments, to have enabled them to adopt an aggressive approach to vector control. Several had large eradication programmes to push back or even eliminate fly belts. Nigeria cleared fly from over some 200,000 km2 of the north of the country and Cameroon opened up some 30,000 km2 of the Adamoua highlands for livestock use. Zimbabwe, after consolidating its barriers to the fly advances, embarked on eradication programmes to eliminate fly from the country and, over many years, substantial progress was made.
The substainability of such programmes was considered to be ensured by the foreseen funding continuation, enabling these governments to carry on pushing back fly belts, using their well-established and experienced field organisations. The on-going nature of the programmes was rarely doubted and the rationale that complete eradication, as opposed to recurrent, containing control measures, was a more cost-effective approach was rarely, if ever, questioned. Also tsetse eradication was seen almost as an end in itself and little attention paid to land use and other government development priorites in terms of area potential.
However, in recent times, this approach was has had to be reviewed as state funding has steadily been eroded, and in some countries, e.g. Nigeria, vector control is now very limited. Others have been luckier and have managed to attract sufficient donor assistance, e.g. Cameroon and the Regional Tsetse and Trypanosomiasis Control Programme (RTTCP) countries of southern Africa, to enable them to carry on with their control/eradication programmes.
This, now almost total, reliance on donor funding, together with the new technologies available, has forced a reappraisal of objectives and strategies.
3. DONOR-ASSISTED PROJECTS
At present only the occasional country, e.g. Botswana, is able to self-finance its active tsetse control measures. In some cases, others are able to fund the supply of trypanocidal drugs to some extent. Otherwise, they have to look to donors for funding and this has implications for any future strategy likely to be employed.
3.1 Development of Policy
Tsetse and trypanosomiasis control has, in the past, been a difficult field into which to attract donors. This reluctance to become involved in large scale programmes has been partly due to donors' doubts about the real cost/benefit ratios from active vector intervention and also in recent years to worries of an environmental nature: in some minds, tsetse have been seen as ‘the saviour of Africa’, protecting supposedly-pristine areas from over settlement and subsequent land degradation. The heavy reliance on insecticides of most control methods in use in recent years has also given cause for environmental alarm, albeit much of it being of an emotional nature.
Numerous environmental studies have helped to allay most of these worries, with side-effects being shown to be largely of a limited and transient nature. Also some cost/benefit exercises have been carried out to demonstrate that, at least in some situations, active tsetse control intervention is worthwhile. In addition, there has been a growing awareness that by doing no tsetse control, we will not save those ‘pristine’ parts of Africa for posterity: as human populations have increased dramatically in Africa, we have seen that these demographic pressures have been forcing people into fly areas, in search of land on which to support their families. Thus these ‘pristine’ areas are being steadily settled with virtually no land use planning or other controls. There is developing therefore an understanding amongst trypanosomiasis control workers and donors that planned tsetse control with controlled settlement does at least offer some hope of sustainable good land use.
With these developments, it has recently been possible to attract donors into this field. However, the wider implications of tsetse and trypanosomiasis control are now taken into consideration, with land use and environmental monitoring incorporated into any large scale project. Nowadays, tsetse and trypanosomiasis is rightly seen as only a part of rural development and efforts are made to incorporate it with all the other development factors. Also, although in many areas trypanosomiasis is the major disease constraint in the livestock industry, it is seen as only part of the total disease complex.
Donor project assistance has steadily expanded over the last 10–15 years. In many instances, it came in to assist short-falls in the financing of already established programmes. For example, the programme set up to eliminate fly from the Adamoua highlands in Cameroon ran in the early years with joint funding from the Cameroon Government, GTZ/German aid and World Bank. In the 1980's, the GTZ funding ceased and, later the Cameroon Government could hardly even fund staff pay. Thus World Bank, who in earlier times had only financed the purchase of insecticides for the helicopter spraying, were being asked to cover virtually the whole budget. In recent years, this funding has been intermittent and this has proved very serious for the programme. The long-term plan had been to clear the major part of the highlands (some 30,000 km2) and then protect the vulnerable reinvasion perimeters with a barrier. Unfortunately when funding became intermittent, the eradication programme had not reached the proposed barriers. As a result, for example, the whole spraying operation for the 1991/92 season (covering some 3,850 km2) did no more than recover the ground lost to reinvasion over the previous 2 seasons when lack of funds had precluded any spraying. This is obviously very poor use of funds and strongly indicates the necessity for continuous ensured funding to reach agreed project objectives. Without such continuity of funding, it is impossible to plan operations, there is poor use of the funds, and the whole credibility of the project is questioned. Staff morale also becomes very low.
Such cases will hopefully encourage donors to realise that if they proposed getting into this field, involving either large scale eradication or control programmes, long term financial support is essential. It is difficult to see the economies of most African countries growing at such a rate in the foreseeable future that they will be able to take over the financing of such programmes themselves.
The GTZ tsetse control programme in Cote d'Ivoire started in 1978, chiefly using German (KFW) aid. It was designed basically to reduce trypanosomiasis challenge throughout much of the savanna regions and encourage the transhumant herds of Zebu to settle in these regions, thereby reducing reliance on imported beef (85% imported in 1978). The area covered by insecticide-impregnated traps, chiefly in use against the riverine species G. palpalis and G. tachinoides is now some 60,000 km2, running from the Burkina Faso border southwards to below Yamoussoukro. The campaign has been very successful with fly populations rapidly reduced by about 98% and trypanosomiasis incidence down typically from about 25 % to 3%. Costs are estimated at only about 25 US$/km2/year. However to date, all costs were covered by the project. There is now a realisation that the donor either has to take over recurrent funding permanently or find a way of cost recovery, e.g. by trying to get the cattle owners to pay. We will return to this aspect later.
It is becoming apparent that donors do not want to become involved in long-term, open-ended, recurrent budget financing of this sort. They appear to be willing to finance the initial investigations, and the development and setting up of techniques and strategies, but these will have to be designed to be self-financing in the future, with either cost recovery from the farmers and/or community involvement. Otherwise it is difficult to contemplate, in the foreseeable economic climate in Africa, how such schemes can be made sustainable.
The E.E.C. has agreed to fund the second phase of the Regional Tsetse and Trypanosomiasis Control Programme in southern Africa. This originally had a very aggressive strategy to eliminate an entire fly belt common to Zimbabwe, Zambia, Malawi and Mozambique: this was considered to be a more cost-effective long term solution to the problem, as difficulties and expenses had risen in the previous policy of protecting areas with established livestock and agricultural production systems from advancing fly. Substantial territorial progress was made in the first phase, but, due apparently to the subsequent discovery by more sensitive sampling techniques of some surviving pockets of fly in the areas presumed clear and also because of worries that the tsetse clearance was getting ahead of any land use plans, the review team advocated a slowing down and consolidation period for Phase 2. There must be concern that this might be a sign also that the donor perhaps cannot be relied upon to fund the original objectives to conclusion. There is therefore a further incentive to try to develop systems and strategies which are self-financing and/or community based within the overall strategy. This is likely to be limited as many areas at present have minimal human settlement.
3.2 National and Regional Approaches
In the past, some countries have developed national strategies for trypanosomiasis control. These evolve as national priorities change and finances allow. Other governments have had virtually no possibility to fund any such control measures and here there is little incentive to develop any strategy to fit within their general disease and development policy: there is often a piecemeal approach based on locally perceived crises. A national strategy is important if the country wishes to attract donor funds. It is also necessary to avoid unwarranted and perhaps unjustified waste of scarce resources.
In countries where tsetse control activities have been substantial in the past and eradication programmes approach national borders, there comes a realisation that unless the neighbouring country is carrying out a parallel policy, then in the future, large amounts will have to be spent protecting the border areas from reinvasion. The Regional Tsetse and Trypanosomiasis Control Programme in southern Africa has developed out of such a situation. A regional multi-disciplinary approach to a common disease problem is a rational development and is to be encouraged, as there are many advantages: it improves the chances of attracting donor funds and leads to a more efficient use of staff, experience and resources.
4. TSETSE ERADICATION OR CONTROL AS AN OBJECTIVE
In the past, the trypanosomiasis control policies of many national control organisations have placed emphasis on eradication and notable successes have been achieved, mainly through the use of ground and aerial application of insecticides, in several countries such as Zimbabwe, Zambia, Botswana, Uganda, Nigeria and Cameroon. However the success of this approach has depended on two main factors:
the ability of the control organisations concerned to effectively mount logistically complex and expensive eradication operations;
the ability to consolidate the areas cleared against reinvasion.
The high costs and complexity of the operations have meant that in virtually every instance, any on-going eradication programmes have recently proved beyond the capacity of national organisations to sustain them without extensive technical and financial support by donors.
The second problem has been the inability of control organisations to protect cleared areas against reinvasion, due to technical difficulties and inadequate finance for barrier maintenance.
In essence, the technical and financial problems experienced by control organisations have meant that while eradication appears to be a superficially attractive option in that it implies a once and for all solution to the problem, this has rarely proved to be the case. These considerations mean that, in cost terms, an eradication strategy is likely to be most attractive when employed against discrete, isolated tsetse populations occupying limited areas or where the presence of substantial natural barriers such as lakes, mountains or areas of intense agricultural settlement limit the extent of any artificial barrier. Financial continuity must be ensured before embarking on such a programme.
4.2. Control or Suppression
The success of this alternative depends largely on whether it is technically achievable, whether it can be achieved at a reasonable recurrent cost and whether the control operations can be made sustainable.
Most of the current tsetse control techniques can achieve significant reductions in tsetse density and could in theory be used: we will discuss their individual and integrated potential later.
As regards to whether it can be achieved at reasonable cost, any fly reduction must translate itself into a concommitant reduction in trypanosomiasis challenge and the benefits ensuing to the affected communities as a result of this reduction must exceed the cost incurred.
Concerning the benefits; ultimately these will depend on:
the extent that a reduction in trypanosomiasis challenge translates into improved health and productivity of affected livestock populations;
the extent that the opportunities presented for the development of more efficient and profitable systems of livestock keeping are taken up by the rural community concerned;
in certain situations, also the extent of the reduction in the risk of human sleeping sickness in endemic areas and of the ensuing benefits to the health and well-being of the human population at risk.
Control or suppression implies continuous, recurrent financial and labour commitments. If it is to be feasible in most countries in the foreseeable future, these commitments will have to be borne very largely by the local communities. Either they must pay directly for the work being carried out by the governmental control department or they must purchase and employ the technologies themselves, perhaps with some limited governmental extension service support.
5. POSSIBLE COMMUNITY INVOLVEMENT IN CONTROL ACTIVITIES
If it is considered that most African governments will not in the foreseeable future be able to fund sustainable tsetse control operations and that donors are only likely to fund the investigation, development and setting up of strategies (as opposed to recurrent funding of on-going programmes), then the implication is that the responsibility for the physical implementation of vector suppression operations and for the financing of the necessary inputs would fall largely on the rural community.
How realistic is this approach and what are likely to be the deciding factors for possible success?
If an approach based on community involvement is to succeed, however, various criteria will need to be fulfilled:
the methodology employed will need to be simple and easily understood by the participants;
the inputs involved should be cheap and preferably obtainable locally or from within the country concerned. It will be necessary to avoid as much as possible the importation of foreign goods, with their foreign exchange implications;
the community must have the ability to organise and sustain the implementation of the control activities. It will need the active cooperation of whole village communities over a long time as individuals acting in isolation are unlikely to achieve any significant suppression of the vector. In sparsely settled areas with few livestock-owning villagers, the individuals concerned will probably benefit greater from relying on drug therapy: here the owners receive the direct benefit in the improved health and productivity of their own livestock.
There are certain conditions where it is considered that such an approach has a better chance of success:-
In areas where tsetse and trypanosomiasis challenges are high and into which grazing pressures elsewhere have by necessity pushed livestock;
where very stable communities, used to carrying out self-help schemes, exist.
Where livestock numbers are high and serious constraints from trypanosomiasis exist (deaths, abortions, low calving rates, low weight gain, etc.), the benefits in return for expenditure on tsetse control are likely to be more immediate and substantial, and act as a further stimulus to the livestock owners. In settled areas, land use practices are usually well established and although there is little legally-based land tenure in Africa, communities regard their occupation as long-established ‘rights’. Mixed farming or agro-pastoral systems may present the most promising situations: they have established residents, with an interest in the long-term productivity of ‘their’ land, who often work hand-in-hand together with neighbours. They are likely to benefit two-fold;-
firstly through the direct benefit to the health and productivity of their livestock, and
secondly through improved crop production and increased acreage through increased draught oxen power.
Much of this is supposition as we have at present little past experience to go on. It is a considered priority for donor-financed programmes to investigate the feasibility of the various techniques (either alone or as an integrated approach) and strategies. It is likely that we can only go so far down this road and there will be many situations where communities are unwilling to cooperate and/or pay, for a variety of reasons. For example, in many poor countries, the consumption of livestock products is actually falling due to the poor general economic situation meaning that the general public cannot afford to buy meat: if there are only pastoral farmers, there may be little take-off from the herds and no cash will come to the livestock owner to allow him to fund tsetse control activities. There are many disease and socio-economic situations to be explored before we find the limits of possible community involvement: it will also be of a slowly evolving, dynamic nature.
It is imperative that these limits are found as there are bound to be many situations where such an approach will not work, for a variety of reasons. In these situations, where demographic pressure in the country is high and good land potential can be demonstated, there will certainly remain a case for donor-assisted programmes to ‘open up’ such areas at ‘government’ expense, to be followed by controlled settlement with sustainable land use practices.
It would be wrong to give donors the impression that community-based tsetse control is likely to be the complete answer to Africa's long-term trypanosomiasis control and subsequent sustainable land use problems. The sooner this can be established, the better.
6. ANALYSIS OF THE POTENTIAL OF MODERN TECHNIQUES FOR TSETSE AND TRYPANOSOMIASIS CONTROL
The following section is a brief review of the different techniques and options currently in use for trypanosomiasis control, with particular reference as to their suitability for control and/or eradication, ammenability to community participation, suitability for large scale use and a general appraisal of their advantages and disadvantages.
6.1 Parasite Control
Drug therapy has had to have been in the past the main control activity in many countries, due to a lack of government funding and vector control infrastructures. Although this has been partially effective, there have been problems of drug resistance, due to drug mismanagement: this is of particular concern as there are few drugs available and this situation is unlikely to change in the foreseeable future. Also a lack of reliable information on the true extent of the problem has not helped in the planning of a national campaign or even the economic justification for it. Drug supplies are usually erratic and ‘revolving funds’ to resolve this have usually ended in failure, as difficulties in recovering monies steadily exhaust the fund. In an effort to improve availability and under some donor pressure, there are currently movements in some countries to hand over trypanocidal drug distribution and sales to the private sector.
Drug prophylaxis should only be considered where a proper drug management system can be established and maintained: this is usually only on large farms and commercial ranches where productivity gains and regular take-off justify such intervention on economic grounds.
6.2 Trypanotolerant Livestock
Most indigenous livestock breeds exhibit a degree of trypanotolerance when compared to the exotics, the trait is particularly pronounced in the N'dama and West African Shorthorn stocks of West and Central Africa.
Although there is a clear potential for the use of such breeds in the humid agro-ecological areas where they have evolved and to which they are adapted, it must be borne in mind that these animals are tolerant only and succumb to trypanosomiasis under high challenge or physiological stress, caused for example by poor grazing under drought conditions. They are probably unsuited to the more arid conditions. Also in these latter areas where the priorities are for high milk production and larger draught animals, owners show a strong preference for the Zebu types, which are considerably more trypanosomiasis-susceptible.
Further within-population selection and possible genetic conferring of trypanotolerance in the N'dama and shorthorn breeds to other breeds may in the long term future lead to a wider use of this trypanotolerant trait.
6.3 Vector Control
6.3.1 Ground Spraying
This technique has formed the backbone of most of the large scale tsetse control efforts from the 1950's into the late 1980's, mainly using DDT or Dieldrin as a single residual deposit on restricted dry season fly habitat. It was the basis of most of the early programmes in, for example, Zimbabwe, Zambia, Nigeria and Uganda.
To minimise the area likely to be lost in the subsequent rainy season through reinvasion, as large an area as possible was treated each dry season, using very large, well-trained and disciplined field teams. If the percentage of the total area needing to be actually sprayed (usually known as % discrimination) could be kept to a low level (usually below 15%), costs were acceptable and, if supervision was good, efficiency in terms of area eradicated as a proportion of total area treated was good. It was seen as a tool to achieve localised eradication as part of ongoing schemes to push back fly belts. Occasionaly ground spraying was used as a control tool to support barriers or to reduce fly challenge in human sleeping sickness endemic areas.
In recent years, the use of ground spraying has declined to very minimal levels, for a variety of reasons:-
environmental pressures against the use of DDT or Dieldrin, particularly in donorfinanced programmes. This was in spite of the fact that only limited parts of the total habitat were treated and side-effects studies showing non-target effects to be largely minimal and transient. Also, the safer synthetic pyrethroid insecticide alternatives push up costs considerably;
appearance on the scene of more environmentally acceptable, and perhaps simpler and cheaper methods such as the use of tsetse traps and targets;
decline in the size and organisational ability of national control organisations, due in part to financial restrictions and in part to declining levels of supervision.
The technique remains a suitable option for eradication of morsitans and palpalis group flies in drier savanna habitats. It is too expensive and requires too much organisation for it to be considered as a control tool, inferring several repeated treatments every year: other alternatives such as traps and targets are superior for this purpose today.
It is not suitable for community-based programmes, mainly because of the technical supervision requirements, but also because of concerns as to the unsupervised use of insecticides.
Given these problems however, it may prove to have a use on a limited scale in the future in the mop-up of populations where, within any large scale eradication programme, for example traps and targets might be experiencing local difficulty. It is impossible to envisage the return to the large scale use seen in the past, in view of the required large, disciplined and organised teams necessary.
6.3.2 Aerial Spraying
126.96.36.199 Helicopter Residual
This technique was used in the past in West Africa in programmes to eradicate the palpalis and morsitans groups of flies from the savanna and guinea zones of Nigeria and is still currently in use chiefly against G.m. submorsitans in the Adamoua highlands of Cameroon.
It basically involves applying a single residual deposit of a persistent insecticide to the more restricted, dry season habitat of the fly. This normally involves treatment of the riparian vegetation, using the helicopter downdraught to force the insecticide through the upper canopy.
The technique is more costly than most, even if percentage discrimination is kept below say 12%. Also the side-effects on non-target organisms are both more acute and longer lasting than any of the other insecticidal techniques. These are the two main factors which have restricted its use and it is unlikely that it will be used any more extensively in the future.
Its one main advantage was that large areas could be effectively and quickly treated with the minimum requirement for trained local staff. For example, 4,000 km2 could be treated with 2 helicopters in 3–4 months of dry season.
Its high cost meant that it could only be considered as an eradication tool: repeated control applications would be too expensive and too environmentally damaging. It is only for use in treating large areas, as setting-up charges for small areas would make costs even more prohibitive per km2. Obviously it is not a tool for community based control.
188.8.131.52 Sequential Aerosol Spraying
This classically involves the use of fixed-wing aircraft applying a sequence (usually 5 or 6 applications at 12–20 day intervals) of extremely low dosage, non-residual, insecticide as a fine aerosol.
It was extensivly used over the last 25 years in eradication programmes against the morsitans group of flies in the savanna situations of southern and eastern Africa, although it has also been used against the palpalis group in West Africa, albeit less successfully.
Its main advantage was that large areas (normally 2,000–6,000 km2) can be treated very quickly (3 months) with a minimal reliance on ground support workers. Also non-target side-effects were comparatively minimal and transient. Although quite expensive, costs were acceptable as long as 90–95% of the area treated was eradicated, with only limited retreatment being necessary.
It could mainly be used only over relatively flat terrain. Due to the relatively high cost, and setting-up organisation necessary, it is most suitable in large scale eradication programmes. It is not economical enough for repeated control treatments and not suitable for small areas or, of course, involvement in community based schemes.
It can have a part to play however in the rapid treatment of large areas in human sleeping sickness epidemics, where there is an urgent requirement for fly population reduction in order to rapidly reduce man/fly contact.
In all the previously mentioned insecticidal techniques, there is a question of sustainability. They must either be employed as part of an ongoing programme to progressively push fly limits back to finally eliminate an entire, discrete fly belt, or the cleared areas must be protected by natural or cheap, effective, man-made, sustainable barriers: the latter are difficult to achieve.
6.3.3 Sterile Insect Technique (SIT)
This technique is only justifiable if the objective is eradication and it can be achieved at reasonable cost. Its advantages of species-specificity and non-contaminating nature are in almost all circumstances outweighed by the high costs and considerable sterile insect production and release logistics.
At best, it could only be considered as a possible method for final mop-up of low density situations over relatively small areas, and even here, there are perhaps cheaper and quicker ways to achieve the same end in most situations.
6.3.4 Traps and Targets
The recent development of relatively efficient traps and targets, often enhanced with attractant odours, has opened up considerable possibilities for the control of many tsetse species in a wide variety of situations. These systems have of course also provided field workers with more sensitive sampling and survey tools.
The palpalis group is much less responsive to the range of synthetic odours developed than is the morsitans group. Even with this former group however, even the odourless traps and targets are sufficiently attractive to be an efficient tool for control. Occasionally the traps are used without insecticides, often with the members of the local community emptying the catching devices on a regular basis: this is seen as a good way of motivating the local community to help in the control activities in sleeping sickness situations.
More normally however, the traps and/or targets are used impregnated with a persistent insecticide, with reservicing every 2–3 months. Thus for example, Vavoua traps impregnated with insecticide are used in the animal trypanosomiasis control programme now covering some 60,000 km2 of the savanna area of Côte d'Ivoire, mainly against the riverine species, G. palpalis and G. tachinoides. Here all the work and costs are borne by the project. However, whilst control activities in the same country against gambian sleeping sickness use the similar system of insecticide-impregnated traps (and targets), the local community is involved to the extent of looking after the devices and re-impregnating them.
As the morsitans group flies have a more widespread distribution throughout their savanna habitat, it has only been with the availability of the synthetic attractive odours, developed from animal breath and urine, that these trapping/killing devices have become relatively efficient. Cattle urine can be used as a cheap alternative to some of the synthetic odours: the latter are quite expensive but as they are only needed in small amounts distributed through a slow release system, their cost as part of the overall technology is not considered high. With a density of as low as only 4 per km2, these attracive devices impregnated with insecticide, have given excellent levels of control, and where the placement and density is adequate, even eradication. The odour-baited, insecticide-impregnated targets currently form the major control basis of the Regional Tsetse and Trypanosomiasis Control Programme (RTTCP) in southern Africa. They also provide useful technology in providing reasonably effective, round-the-year barriers against possible reinvasion.
The potential advantages of these trap and target systems are well known. The technology is relatively simple and is certainly less environmentally polluting than the other insecticidal methods: they are largely target species specific.
As far as cost is concerned, they are the cheapest alternative if control on a recurrent basis is the chosen strategy. In the control strategy in the animal trypanosomiasis programme in north/central Côte d'Ivoire, the costs were given as about US$ 25/km2 or, perhaps more importantly, given the livestock density, less than the cost of a single curative Berenil injection per year. This was for a reduction in general traditional herd infection rates from about 25% to less than 3%. For the human sleeping sickness control in the same country, but where community participation is involved, costs were only about US $ 100/km2 in the first setting-up year, dropping thereafter to about $25 per year.
Cost advantages in using such techniques over others for eradication are less clear. The final cost per km2 depends largely on how quickly the system eradicates the fly. For example, earlier comparative costings for the targets in the RTTCP were given on the basis that the technique would eradicate in about a year. However, in reality, many of the areas have retained targets now for 3 or 4 years continuously without the stage being reached where they could safely be removed. In such cases, the accumulated cost per Km2 over this extended period of time needs to be taken into account when comparing cost-effectiveness with other methods of vector control.
There is no doubt that the trap/target methods are very good for small scale operations against the palpalis and morsitans groups of tsetse but for large scale use, there are some of the logistical demands as exist, for example, for the successful implementation of ground spraying. It is necessary to have a well-trained, well-motivated, disciplined field force under good supervision and with good pre-planning. This is especially important in eradication campaigns where cost-effectiveness relies on the rapid achievement of the eradication goal. If target siting and maintenance is sloppy, eradication will take much longer to achieve and unit area costs steadily mount.
Practical field problems do exist, with possible loss of targets through theft, damage from human, fire or animal sources, and, especially in riverine species control, loss of traps/targets through wash-away in the rainy season. All these factors very from one situation to another. Some programmes suffer minimal theft whilst in others, e.g. Somalia, it was substantial. Even in countries where there have been few losses through theft over a long period, possible economic changes or other problems can result in sudden serious surges in theft, as has happened recently in the border areas of Zimbabwe and in Zambia.
Good and regular trap/target maintenance is essential to the effectiveness of the devices. If the grass around the devices is not kept down, they are less visible to the flies, and also if their movement in the wind is thus restricted, attractiveness is further impaired.
Reservicing makes up a large part of the overall cost. Earlier, sufficient insecticide deposit and odours were placed to remain effective for 3 months but recently, in an effort to reduce reservicing visits, successful trials have been carried out to see if sufficient insecticide and odour can be placed to last, for example, for a year. It must be pointed out however that this is only an option where previous experience has shown that theft or other damage is minimal in the area concerned: it is obviously of no help to visit targets after a year, only to find most of them stolen, perhaps many months previously.
A major advantage of such trap/target techniques is that, perhaps alone amongest the current vector control methods, they lend themselves to possible community participation. Whilst it has been shown that it is relatively easy to involve communities in the labour and perhaps cost of any such system where human sleeping sickness is involved, it is far less clear how amenable such a strategy would be in controlling animal trypanosomiasis, particularly in the traditional livestock sector. Some minor programmes have strated to look at this and, since the current donors wish to encourage this approch in an effort to develop self-financing, sustainable systems, it is imperative that every effort is made to see how far it is possible to go down this road.
There are bound to be limitations and it is important therefore that a flexible approach is maintained, to cater for all situations. In traditional livestock situations where the poor economy or traditional attitudes mean little take-off and therefore little ready cash, will the farmer be able to fund such activities?. Will the community as a whole be prepared to get involved? Will any activities be sustained? How much government extension support will be necessary to help set up and monitor such schemes?.
Such schemes perhaps have the best chance of success where:-
communities are well established and settled and used to participating in communal self-help schemes. Mixed agro-pastoral farmers often have more incentive to look after their land and invest in it;
trypanosomisis challenge is high and losses directly attributable to the disease are considerable. This is happening more often as demographic pressures and increases in livestock numbers are causing overgrazing, thereby forcing cattle owners further into the fly belt edges in their search for pasture.
6.3.5 Insecticide Treated Livestock
This recently developed technology can be regarded as a modification of the target method whereby, instead of stationary traps or screens, insecticide-treated domestic animals, primarily cattle, can be used as attractive, moving targets.
The insecticides are applied by dipping or the use of individual “pour-on” applications.
The dipping of cattle, combined with the use of “pour-on” where dips are not available/working, in areas of G. pallidipes and G. morsitans infestations in Zimbabwe has led to a very high degree of vector suppression and trypanosomiasis control. However, for it to have a good chance of success, it is considered necessary that:-
domestic livestock must be present in the area in sufficient numbers;
cattle must represent the overwhelming proportion of the host complex of the tsetse in the area;
most of the cattle must be presented for treatment on a regular basis.
Very often, these criteria are only met on commercial ranches but can be present in traditional herd areas where regular and virtually free treatment ensures a high proportion of presentation for treatment: such was the situation in north-east Zimbabwe. Very often in such situations, there is already in existence a dipping infrastructure for control of tick-borne diseases.
The cost/benefit ratio of such an approach must be examined in any situation to see if it is worthwhile. It has to be more cost-effective than a chemoprophylaxis regime, although the latter is only considered an option in areas of relatively low disease challenge.
As regards to the possible successful use of this approach in community-based programmes of trypanosomiasis control, there is little experience to date. There is some evidence that, if cattle owners are asked to contribute (even only part-cost) towards the dipping of their livestock previously done free by government veterinary agencies, the numbers presented on a regular basis drops considerably. Although the individual cattle treated would benefit from some protection, this low-level presentation would be unlikely to have an appreciable long-term effect on the tsetse population.
In some countries, e.g. Burkina Faso, where there is no dipping infrastructure and drug supply is intermittent, efforts are being made to promote the “pour-on” application in some situations. Here settled agro-pastoralists have suffered grievous trypanosomiasis losses in the past and seem willing to invest in such a control strategy. They see the direct cost of the control measure directly applied to their own animal. However, it may be that for good control results, such treatments may have to be backed up with the strategic placement of some traps or targets in areas of higher fly density. Again the various scenarios need to be investigated.
To achieve an effective degree of vector suppression, it will be necessary to find out, in the various situations, the proportion of animals that need to be treated and the treatment intervals required: extending treatment intervals as far as possible would obviously reduce annual costs, but some care needs to be taken here with regard to any possible deleterious effects on the enzootic stability of tick-borne diseases.
6.3.6 Integration of Various Methodologies
As has already been indicated, all the available control techniques have their advantages and disadvantages, and no single method is the best option in every situation. In any large-scale programme, it is a question of deciding whether eradication or control is the preferred approach and then deciding on the most cost-effective method, given the local infrastructure. In practice, there are many different situations requiring different methods and an integrated approach is necessary. This can mean using different techniques in adjacent areas or using two or more overlaid techniques in the same area, i.e. one to achieve the major suppression and a follow-up one to eliminate the residual population.
In view of the likely heavy reliance on donor funding in the foreseeable future, it is becoming even more important that the long-term viability of any proposed intervention programmes centred on tsetse and trypanosomiasis control is ensured as far as possible. This means through studies on land use, taking into account present practices and future area potential. All other disease and related development factors which have any bearing on this problem must be taken into consideration to ensure that it is part of a total rural development package. The long-term cost/benefit ratios of any such intervention actions must be positive.
When considering the opening up of ‘new’ areas, preliminary studies should help to identify priorities with regard to area potential.
In all situations, the option of eradication as opposed to recurrent control must be considered. Although eradication implies a one-off financial and technical commitment, it can prove difficult to achieve. The option of having to protect locally cleared areas from reinvasion by the use of man-made barriers needs particular strong analysis as such barriers are rarely complete or sustainable.
If the eradication option is chosen, then the degree of aggressiveness, in the use of the techniques chosen, can be important in overall cost-effectiveness and manpower requirements: if superficially more expensive techniques can achieve eradication quickly, they may be a better option than other methods which, though potentially cheaper, may prove more expensive if eradication takes longer than expected to achieve. It is important in any large-scale programme to keep an open mind towards the whole range of techniques available, as varying situations are almost certainly going to require an integrated approach to the problem. Linked to this integrated approach should be progress towards coordinated regional programmes.
With regard to donor interests and general long-term sustainability, particularly of trypanosomiasis control (as opposed to eradication) strategies, it is imperative that we explore the full potential of community participation as soon as possible. Whilst there are likely to be some situations where the costs and implementation of such an approach can be totally borne by the community, in reality many situations are going to require ongoing government financial and technical back-up support. There are also likely to be situations where severe demographic pressures justify the opening up of unsettled areas with good land potential, and much of the initial cost of this is going to have to be borne by government and/or donor.
Careful planning and the choice of the right options will be crucially important in ensuring sustainability, both in terms of results achieved and funding support. Lack of financial continuity has perhaps been the main factor in the breakdown of past programmes, leading to a subsequent lack of credibility in some important quarters.