R. Allsopp1
INTRODUCTION
1. The amount of research which has been associated with the development of methods for controlling tsetse and trypanosomiasis is immense. It still continues in abundance yet the disease and the vector are, arguably, as widely distributed and as problematical as they ever were (Rogers and Randolph 1986; Vale 1987). They have retreated in some areas, largely as a result of urbanisation rather than the practical application of research findings, but, even where their existence is threatened by severe ecological change, both have proved alarmingly adaptive and tsetse persist in ‘peridomestic’ pockets (Jordan 1989).
2. In reviewing research progress we must therefore ask ourselves whether it has been satisfactory in contributing to the control of trypanosomiasis, which is the ultimate objective.
3. To this end it is necessary to:
clearly define the objectives of tsetse and trypanosomiasis control
consider how control techniques have developed and whether they have achieved these objectives
assess how research activities have contributed to the development of these techniques.
The objectives of tsetse/trypanosomiasis control
4. Animal trypanosomiasis is a constraint to livestock production and therefore to rural development in general (Tacher et al 1988). Livestock are economically and socially important components of agricultural production systems. Jahnke (1988) identified their particular value for meat and milk in pastoral systems, labour, manure and ‘social value’ in agropastural systems, income generation in modernised production systems. The same author estimates that trypanosomiasis elimination would result in an additional 1 million tons of meat-equivalents per year in Africa.
5. Elimination of this disease is only one consideration in the management of an “agricultural production system” or “farming system” which will have many interacting productivity constraints. These might include a range of health problems, nutrition, and characteristically where trypanosomiasis occurs, climate and water resources. They might also include livestock quality (breeding), husbandry practices and other socio-economic factors. These interacting constraints do in effect characterise the system.
6. The value of removing a particular constraint, perhaps by eliminating a vector population, depends to a great extent upon these many interactions. The manner in which control is effected depends entirely upon the resources available to or within the system.
7. If viewed in this context, both tsetse and trypanosomiasis control and the research which supports them will have obvious production objectives i.e. they will be problem led. If not considered as components of a farming system, the control operations themselves become objectives and associated research, technology driven. In recognising this, the FAO Panel of Experts which met in Accra, 1988, (FAO 1989) concluded that “tsetse control can no longer be seen as an end in itself”.
Tsetse control techniques
8. Looking back at the excellent and dedicated work that has been carried out in the search for improved control techniques it is apparent that tsetse control has seldom been viewed as a farming system problem. Both tsetse flies and trypanosomes are intriguing, challenging and adaptable foes against which to pit one's intellect. This has been reflected in the amount and variety of research activity they have attracted and in the restricted vision which often accompanies the application of this research to control attempts.
9. Tsetse control has relied heavily upon the use of insecticides for more than forty years (Allsopp 1984) and where 'integrated' control has been reported (Hursey and Allsopp 1984), it was usually a combination of chemical control techniques rather than a truly multidisciplinary approach.
10. Chemical control techniques are well documented and well known. Ground spraying (Lovemore 1978, MacLennan 1967) and low dosage sequential aerial spraying (Allsopp 1991) have achieved considerable success in reducing fly populations. Aerial spraying remains the most effective “fire brigade” approach where speed and scale of operation are major considerations. Associated research has tended to be aimed at reducing the amounts of insecticide applied; indeed this was the raison d'être for the development of sequential aerial spraying. Their development has been rather more empirical than scientific and their application is dependent upon central government or institutional involvement. The transfer of technologies has also, therefore, been restricted to this level of intervention.
11. Cattle dipping or spraying with broad spectrum pyrethroid insecticides is gradually being investigated (Wilson 1987; Thomson 1987) and is a promising technique which interacts with tick control.
12. Most recent attention has focussed on the development of traps and impregnated targets combined with the use of odour baits (Vale 1987). The technology is extremely adaptable and can be managed at both institutional or community level. It has been particularly associated with good science although it's elegance and environmental appeal have perhaps too strongly highlighted a unilateral tsetse control solution to the problem of trypanosomiasis.
13. Irrespective of the techniques used to control tsetse or trypanosomiasis, the result will almost inevitably include some environmental change. To justify these controls, this change must represent an increase in productivity. It must not erode the system's resource base. The key to this is sound management and sustainability. Control operations which are too rapidly or directly the product of basic research, irrespective of it's quality, are more likely to prove fragile and unsustainable. Such problems are well recognised and have to some extent been addressed by the call for tsetse control to be carried out only in conjunction with land use plans (Kemf 1988; Mulder 1989). Land use planning is generally an institutional prerogative and it does not necessarily equate with the management of farming system resources. In reviewing the land-use implications of the EC's Regional Tsetse and Trypanosomiasis Control Programme for Southern Africa, the IUCN concluded that tsetse control and land use planning should be elements of integrated rural development (Stevenson 1988).
14. In reality it is not so difficult to kill tsetse flies. We already have a variety of techniques which have proven to be effective though they may not always be fashionable. Reinvasion continues to be a problem and must remain a priority consideration until such time as it might possibly be overcome by the 'farming systems' approach. There is, however, little justification for much more research into new control technology.
Research associated with tsetse control
15. Agricultural research is sub-divided by Farrington (1989) into:-
Basic research: generates new understanding of biological processes
Strategic research: addresses issues which influence the efficiency with which other research downstream can be carried out
Applied research: seeks to create new technology
Adaptive research: adjusts technology to specific environmental or socio-economic conditions.
16. All four categories are important and all should be recognised in developing research programmes. Tsetse research has embraced all four but the latter is the only type of research with the primary objective of developing techniques which address specific resource management problems. It is dependant upon an understanding of environmental and socioeconomic considerations i.e a knowledge of the farming system. It is the most neglected.
17. This can be illustrated by reference to developments in the field of odour-bait technology, which is unquestionably the oustanding contribution to tsetse research in recent years.
18. The successful development of odour bait technology is a testament to the multidisciplinary scientific approach and the utilisation of all four scientific categories mentioned above; although rather fewer that are truly adaptive.
19. Basic “host seeking” behavioural research resulted in the introduction of the biconical trap (Challier and Laviessiere 1973) and the use of odour attractants to enhance the visual appeal of these and other trap types (Vale 1974a). Together with the exploitation of electric nets to assess trap efficiencies (Vale 1974b) this research provided the springboard from which a profusion of research initiatives were launched. Central to the odour studies were sophisticated physiological and chemical techniques to identify specific components of host odour which are attractive to tsetse and can be synthesised (Hall, 1990; Laveissiere et al 1990). Also fundamentally important, as in all pest management situations, has been our increasing understanding of tsetse population dynamics (Williams et al 1990; Hargrove 1990).
20. A wide range of both field and laboratory based strategic and applied activity helped transform these basic research outputs into practical survey and control tools such as the chemically impregnated target (Vale et al 1988), the monoconical trap (Lancien 1981) and the Ngu trap (Brightwell et al 1987).
21. These were further improved through field and wind tunnel studies on attractant colours (Green 1986), video recording of trap orientated behaviour (Brady et al 1989), the use of geographical information systems to identify suitable deployment strategies (Williams et al) 1989) and a multitude of general odour studies (Bursell 1984; Hargrove and Vale 1978; Vale 1980; Vale and Hall 1985; Torr 1990).
22. Appropriate insecticides (Torr 1985) and chemosterilants (Hall and Langley 1987; Langley and Hargrove 1990) for applying to traps and targets have been studied in the laboratory and field tested.
23. Some research has been carried out to adapt odour bait technologies to specific local conditions and, where appropriate, encourage community participation (Otieno and Dransfield 1990, Kenya; Leygues and Gouteux 1989, Congo; Ferrara 1987, Ghana). There has been a more active involvement in this type of research with human sleeping sickness in West Africa but there are fewer examples relating to animal trypanosomiasis. Without sufficient attention to adaptive research the probability of logistical or social problems, notably theft, are increased (Hursey et al 1988, Zimbabwe; Lee C W pers comm., Somalia; Mawuena and Yacnambe 1988, Togo).
General recommendations for future research
24. It is not possible or desirable to change research directions at a stroke and expect an entirely new research strategy to be widely adopted, but there is a need for change and it will have to be orchestrated by funding organisations. In general, the research emphasis should shift from left to right along the line basic - strategic - applied - adaptive. We must keep an open mind about new control techniques but this should not now be a research priority. There is still room for further technological improvement, but even this must be close to reaching the point where it suffers the law of dimishing returns; aerial spraying is a particular case in point.
25. The scale of the trypanosomiasis problem has barely dimished, it is vast and complex. In order to make any significant inroads the research approach must be in proportion. This will only be achieved by making effective use of computerised systems and mathematical modelling; discussed at length for human sleeping sickness at a UNDP/World Bank/WHO workshop (de Muynck and Rogers 1989). In this way it may be possible to take the overview yet put local problems into perspective and focus attention on specific farming systems.
26. Three basic guidlines are recommendations for future tsetse/trypanosomiasis research:
Tsetse control must cease to be an end in itself
We should concentrate on adapting established techniques, particularly odour bait techniques, within a farming systems context; rather than seeking new methods. There is a danger that this will gradually result in the fragmentation of the highly motivated and cohesive 'tsetse research' community and in order to maintain their considerable momentum there will be a vital role for international bodies such as FAO to redirect and coordinate future activities.
We must define and understand farming systems, i.e. identify their objectives, resources and production constraints, understand the epidemiology of trypanosomiasis and other diseases then adapt technologies to reduce or eliminate them in an integrated, cost effective and sustainable manner.
Research should be appropriate and must be translated into practical operational procedures. This is not a call to limit research activities to those which are 'onfarm' or 'farmer participatory' although these will have a place. There is a continuing need for a basic research and good science but this should be problem-driven, multidisciplinary and followed downstream to operational implementation. Interventions will be necessary at all levels within agricultural production systems and this must be anticipated at the outset to ensure technology transfer. At the higher institutional levels this will require properly targetted training. At the farmer level it will depend upon agricultural extension or possibly farmer participation.
Specific recommendations for future research
27. Farming systems research is possibly as convoluted as trypanosomiasis research; entire papers are dedicated to definitions (Fresco 1984; Sands 1985). It would be unwise to delve too deeply into it's socio-economic complexities or see it only in terms of the resource poor farmer.
28. Nevertheless, it is essential that we understand farming systems and their production constraints. Agro-pastural communal farming systems represent a considerable proportion of arid and semi-arid agriculture. In such systems, sustainability is likely to be dependent upon community participation which in turn will require adaptive and largely on-farm research to define their physical structure, socio-economics, nutritional and general animal health problems; and how these interact. Trypanosomiasis research must embrace these disciplines and involve appropriate expertise from the outset.
29. Where trypanosomiasis is a constraint to large commercial production systems or widespread pasturalism, intervention and technology transfer will be at a higher level. Similar parameters will need to be defined, but in these cases research and development will most likely be the undertaken by central goverment or commercial institutions.
30. Irrespective of the specific farming system or the level of intervention, geographical information systems (GIS) provide the ideal mechanism for integrating the many spatial and temporal variables within farming systems or indeed agro-ecosystems. They provide a means by which huge amounts of data can be stored, and analysed. They facilitate the integration of various epizootiological data, the identification of common factors and they reduce duplication of effort. Together with remotely sensed imagery, they also provide an effective means of illustrating past changes or monitoring future changes in land use patterns. This could prove invaluable for defining appropriate control strategies and predicting their probable outcome.
31. A number of institutions already have experience in the use of GIS for collating epidemiological data or in remote sensing. These include UNEP, ISPRA, ILRAD, Oxford University, the Natural Resources Institute, the Nairobi Remote Sensing Centre etc.. These institutions should be encouraged to coordinate or support activities which address specific problems perhaps supervised by a steering group of experienced representatives under the auspices of FAO.
32. Mathematical modelling is an essential requirement for translating GIS data into practical and useable information. It provides the means by which gaps in our knowledge can be detected, thus identifying research or control requirements, and it is the vehicle by which this information can be used predictively.
33. To bring this report back more clearly to it's main theme, i.e. tsetse and trypanosomiasis, there is a need for further studies of the trypanosomiasis disease complex itself i.e. epidemiology (epizootiology).
34. At the macro scale, tsetse distribution maps are well out of date (Gouteux 1990). Remote sensing can be applied to the identification of habitats for parasites and disease (Hugh-Jones 1989) and Rogers and Randolph (1991) have shown that the distribution and abundance of tsetse flies can be related to normalised difference vegetation indices (NDVIs). In concert with the GIS approach mentioned above, the use of remote sensing to define these wider epidemiological parameters should be pursued.
35. After many years of fruitless searching for trypanosomiasis vaccines, research at the tsetse trypanosome interface may provide important information on the vectorial role of tsetse and thus on the transmission of the disease (Jordan 1990: Baker et al 1990). This is a clear reminder that tsetse and trypanosomiasis research are interdependant and should continue to be seen in this light. This work is of epidemiological significance in the trypanosomiasis field but if corroborated may have relevance to other vectorial disease situations.
36. Finally, the need for integration and multidisciplinarity in research and control must be reiterated. Of the many related aspects which should be considered, perhaps two merit particular attention. These are trypanotolerance and nutrition.
37. As the costs of insecticide, drugs, manpower, transport etc. escalates it will become increasingly cost effective to utilise livestock which exhibit some natural resistance to trypanosomiasis. It is also environmentally sensible. Recognised trypanotolerant breeds such as the N'dama are productive and highly capable draught animals. The potential for their wider use should be investigated and their merits perhaps more widely advertised. Many other indigenous breeds exhibit varying degrees of trypanotolerance and this characteristic could be selectively developed to complement other disease suppression or avoidance techniques.
38. The effect of nutrition on trypanotolerance is not clearly understood, indeed the entire question of nutritional stress requires investigation. A combination of strategically deployed, partially trypanotolerant livestock and supplementary feeding might allow cattle to co-exist, cost-effectively with trypanosomes. If community management of disease is indeed to be a way forward in this seemingly endless search for sustainable control, co-existence with the disease may be one answer and timely research in this direction may prove particularly productive.
REFERENCES
Allsopp, R. (1990) A practical guide to aerial spraying for tsetse control. Aerial Spraying Research and Development Project Final Report Volume 2. EEC Delegation, Harare, Zimbabwe.
Baker, R.D., Maudlin I., Milligan P.M.J., Molyneux D.H. and Welburn S.C. (1990) The possible role of rickettsia-like organisms in trypanosomiasis edidemiology. Parasitology 100(2): 209–217
Brady J., Gibson G. and Packer M.J. (1989) Odour movement, wind direction and the problem of host finding by tsetse flies. Physiological Entomology 14(4): 369–380
Brightwell R., Dransfield R.D., Kyorki C., Golder T.K., Tarimo S.A. and Mungai D. (1987) Tropical Pest Management 33: 151–159
Bursell E. (1984) Effects of host odour on the behaviour of tsetse. Insect Science and It's Application 5: 345–349
Dransfield R.D., Williams B.G. and Brightwell R. (submitted) Control of tsetse flies and trypanosomiasis - myth or reality. Parasitology Today.
Ferrara B. (1987)The approach of integrated rural development and the improvement of areas freed, or to be freed, of tsetse flies. Tropicultura 5(1): 34–38
Gouteux J.P.(1990) Current considerations on the distribution of Glossina in West and Cetral Africa. Acta Tropica 47(3): 185–187
Green C. (1986) Effects of colours and synthetic odours on the attraction of Glossina pallidipes and G morsitans morsitans to traps and screens. Physiological Entomology 11: 411–421
Hall D.R. (1990) Use of host odour attractants for monitoring and control of tsetse flies. In Behaviour Modifying Chemicals for Insect Management edited by R L Ridgeway, R M Silverstein and M N Inscoe. Marcel Dekker, New York. pp 517–530
Hall M.J.R. and Langley P.A. (1987) Development of a system for sterlizing tsetse flies. Medical and Veterinary Entomology 1: 201–210
Hargrove J.W. and Vale G.A. (1978) The effect of host odour concentrations on catches of tsetse flies (Glossinidae) and other diptera in the field. Bulletin of Entomological Research 68: 607–612
Hursey and Allsopp (1984) The eradication of tsetse flies (Glossina spp) from western
Zimbabwe by integrated aerial and ground spraying. Tsetse and Trypanosomiasis Control Branch, Zimbabwe.
Hursey B.S., Whittingham G.W. and Chadenga V. (1988) Integration of insecticidal techniques for the control and eradication of Glossina morsitans in north-east Zimbabwe. OAU/CSTR publication no 114, Nairobi. pp 438–452
Jordan, A.M. (1989) Man and changing patterns of the African Trypanosomiasises. In Demography and vector-borne diseases. Edited by M W Service. CRC Press, Boca Raton, USA. pp 47–58
Jordan, A.M. (1990) Tsetse research and control. Bulletin of Entomological Research 80(2): 117–120
Kemf, E. (1988) To kill or not to kill tsetse. Development Forum 16(2): 4
Lancien, J. (1981) Description du piege monocoque utilisé pour l'élimination des glossines dans la Republic Populaire du Congo. Cahiers ORSTOM serie Entomologie medicale et Parasitologie 19: 235–238
Langley, P.A. and Hargrove J.W. (1990) Control of tsetse using pyriproxifen-baited traps and targets. Advances in Invertebrate Reproduction 5: 403–409
Laveissiere, C., Vale G.A. and Gouteaux J.P. (1990) Bait methods for tsetse control. In Appropriate Technology for Vector Control edited by C F Curtis. CRC Press, Boca Raton, USA. pp 47–73
Leygues, M. and Gouteux, J.P. (1989) La lutte communautaire contre une épidemie tropicale: croyance surnaturelle et pieges a tsetse au Congo. Social Science and Medicine 28(12): 1255–1267
Lovemore, D.F. (1978) Planning for tsetse control operations. Rhodesia Science News 12: 137–140
Mawuena, K. and Yacnambe, S. (1988) L'utilisation des pieges et ecrans d'insecticide pour la lutte contra la trypanosomiase animale. Trypanotolerance et Production animale. No 5: 85–92
Mulder, J. (1989) Control of the tsetse fly in Africa and the environment. Courier No. 115: 11–12
Otieno, L.H. and Dransfield, R.D. (1990) Towards the community based and sustainable tsetse management - a report by the ICIPE tsetse programme. Rural Development in Practice 2(1): 31–32
Rogers, D.J. and Randolph, S.E. (1986) Distribution and abundance of tsetse flies (Glossina spp). Journal of Animal Ecology 55: 1007–1025
Rogers, D.J. and Randolph, S.E. (1991) Mortality rates and population density of tsetse flies correlated with satellite imagery. Nature (in press).
Thomson, M.C. (1987) The effect on tsetse flies (Glossina spp) of deltamethrin applied to cattle either as a spray or incorporated into ear tags. Tropical Pest Management 33 (4): 329–335.
Torr, S.J. (1985) The susceptibility of Glossina pallidipes Austen to insecticide deposits on targets. Bulletin of Entomological Research 75: 451–458
Torr, S.J. (1990) Dose responses of tsetse flies (Glossina) to carbon dioxide, acetone and octenol in the field. Physiological Entomology 15: 93–103
Vale, G.A. (1980) Field studies of the responses of tsetse flies (Glossinidae) and other Diptera to carbon dioxide, acetone and other chemicals. Bulletin of Entomological Research 70: 563–570
Vale, G.A. (1987) Prospects for tsetse control. International Journal of Parasitology 17 (2): 665–670
Vale, G.A. and Hall D.R. (1985) The role of 1-octen-3-ol, acetone and carbon dioxide in the attraction of tsetse flies (Diptera: Glossinidae) to ox odour. Bulletin of Entomological Research 75: 209–217
Vale, G.A., Lovemore, D.F., Flint, S. and Cockbill, G.F. (1988) Odour-baited targets to control tsetse flies Glosina spp. in Zimbabwe. Bulletin of Entomological Research 78: 31–49
Williams, B.G., Dransfield, R.D., Brightwell, R. and Kruska, R. (1989) Use of GIS and remote sensing in the study of tsetse populations. WHO Meeting on Information Storage and Retrieval, Geneva 14–18 November 1989.
Wilson, A. (1987) A preliminary report on a large scale field trial to assess the effect of dipping in deltamethrin on the incidence of trypanosomiasis in cattle in a tsetse infested area. Internal report. Department of Veterinary Services, Harare, Zimbabwe.
REVUE DES TRAVAUX REALISES DANS LE DOMAINE
DE LA RECHERCHE ET DU DEVELOPPEMENT AFIN DE SOUTENIR
LES PROGRAMMES DE TERRAIN
RESUME
R. Allsopp
Si on passe en revue les progrès en matière de recherche, il est nécessaire de:
La trypanosomiase animale est une contrainte au développement de l'élevage et au développement rural. L'élimination de la maladie n'est qu'un facteur dans la gestion d'un système de production agricole qui doit faire face à de nombreuses contraintes. Bien que vu dans ce contexte, à la fois le contrôle de la trypanosomiase et des tsé-tsé, et la recherche devraient être dirigés afin de résoudre des problèmes spécifiques. Autrement, les opérations de contrôle deviennent les objects et la recherche qui y est associée, la technologie meneuse.
Le contrôle des tsé-tsé s'est beaucoup appuyé sur l'utilisation des composés chimiques. Plusieurs méthodes de dispersion sont évoquées, dont la plus récente et la plus populaire, celle des pièges et des écrans imprégnés. le contrôle, presque inévitablement mène à des modifications environnementales. Cela devrait entrainer un acroissement de la productivité et ne pas éroder les ressources, à la base.
Nous disposons de toute une gamme de méthodes de contrôle. Il est difficile de justifier des recherches vers de nouvelles technologies.
La recherche agricole peut être sub-divisée en: basique, stratégique, appliquée et adaptée. La dernière necessite une connaissance des facteurs socio-économiques et de l'environnement. Celle-ci est la plus négliée (en matière de trypanosomiase).
Recommandations pour de futures recherches:
Pour être à la hauteur du problème que représente la trypanosomiase, il est nécessaire d'utiliser des modèles et des systèmes programmés. Plus d'efforts devraient être déployé afin de comprendre les problèmes épidémiologiques. La recherche devrait être intégrée et multidisciplinaire. Elle devrait aborder des sujets tels que la nutrition et la trypanotolérance.
