SECTION B - ABSTRACTS

1. General (including land use)

The trypanosomiases consist of a group of important animal and human diseases caused by parasitic protozoa of the genus Trypanosoma. In sub-Saharan Africa, the final decade of the 20th century witnessed an alarming resurgence in sleeping sickness (human African trypanosomiasis). In South and Central America, Chagas’ disease (American trypanosomiasis) remains one of the most prevalent infectious diseases. Arthropod vectors transmit African and American trypanosomiases, and disease containment through insect control programmes is an achievable goal. Chemotherapy is available for both diseases, but existing drugs are far from ideal. The trypanosomes are some of the earliest diverging members of the Eukaryotae and share several biochemical peculiarities that have stimulated research into new drug targets. However, differences in the ways in which trypanosome species interact with their hosts have frustrated efforts to design drugs effective against both species. Growth in recognition of these neglected diseases might result in progress towards control through increased funding for drug development and vector elimination.

Economic and social development requires to be underpinned by health, science and technology. Despite this, infectious diseases hamper poor and marginalized populations, due to failure to use existing tools effectively, to having inadequate tools, and to having insufficient knowledge. Because of these constraints, there are "neglected diseases" (HIV-AIDS, TB, malaria) and "most-neglected diseases" (sleeping sickness, Chagas’ disease) which need much greater attention in the area of drug development. Solutions to the present unhappy state will require (amongst other things) due recognition to be given to targeted research using the full potential of modern science and technology, with proper regard to policy making and the generation of a new, international pharmaceutical policy for all neglected diseases. The different perspectives of the problems of infectious and parasitic diseases, as adopted by specialists in the various disciplines involved, need to be resolved.

This paper discusses past and present approaches to managing tsetse-transmitted animal trypanosomosis in Africa and describes the three main weaknesses of these approaches, i.e., inappropriate objectives, inadequate links between research and policy-making and a lack of recognition that trypanosomosis should be high up on the social science research agenda. Making progress in managing trypanosomosis has been difficult and the authors argue that the weaknesses of the approaches must be corrected if Africa is to benefit from the few advances made so far, and for the continent to make further sustained efforts to combat the disease. The authors explain that this can be achieved by replacing the current widespread preoccupation among researchers and policymakers with controlling (or eradicating) trypanosomosis with a focus on managing (or coping with) the disease. In addition, ways of achieving greater coherence between research and policy-making must be explored. Finally, the social science issues raised by the question of which practical steps need to be taken to manage trypanosomosis in Africa should be placed at the forefront of research efforts.

Setting priorities for health research is a difficult task, especially for the neglected diseases of the poor. A new approach to priority setting for tropical diseases research has been adopted by the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases (known as the TDR). Priorities are defined on the basis of a comprehensive analysis of research needs and research opportunities for each of the ten major tropical diseases in the TDR portfolio. The resulting strategic emphasis matrix reflects the priorities for tropical diseases research from the perspective of the TDR. Its purpose is not to impose global research priorities, but it is believed that the results could be useful to other organizations.

Peri-urban dairy cattle farms within 50 km of Bobo-Dioulasso were studied to assess herd type, disease incidence, management, feeding and breeding strategy. Out of 417 cattle farmers, 42 percent had dairy objectives and were studied. Among these peri-urban dairy farmers, 60 percent were settled, 36 percent semi-settled, and 4 percent transhumant. In total, they held 4558 dairy cows, of which 32 percent lactated during the study. The prevalence of mastitis (55 percent) increased (p<0.05) with herd size. Advanced strategies for supplementary feeding and breeding were most frequent in small herds (<30 cattle). None of the large herds (>60 cattle) had advanced breeding strategies. Bulls and cows were culled at younger ages in herds with better breeding strategy. Overall, this resulted in higher individual milk offtake in small herds (2.46 litres/day) compared with large herds (1.25 litres/day). Pure breeds were rarely used, and the presence of Bos taurus Baoulé naturally selected for trypanotolerance was low. The prevalence of trypanosomosis (40 percent) in herds dominated by Bos indicus Zebu and Méré (Zebu × Baoulé) is an argument for maintenance of biodiversity and selection of Baoulé for milk production.

This paper presents a framework for conceptualizing crop-livestock integration along four dimensions: space, time, management and ownership. The framework highlights the fact that benefits from crop-livestock interactions can be gained by integration along one, some or all of these dimensions, although the space dimension is particularly important. The implications of four factors - the ‘sustainability imperative’; the human, livestock density relationship; the ‘livestock revolution’; and large-scale tsetse clearance - are then explored in relation to the claim that greater crop-livestock integration should be the basis of agricultural development in West Africa. The conclusion of this analysis is that greater crop-livestock integration is likely to be of interest primarily in ‘middle’ countryside areas with relatively good natural resources.

The success of large-scale cattle ranching in African savanna vegetation has often been limited by problems of bush encroachment and disease (in particular trypanosomiasis spread by tsetse flies). Mkwaja Ranch, occupying an area of 462 km² on the coast of Tanzania, is a recent example of a large ranching enterprise that failed within the savanna environment. It was closed in 2000 after 48 years of operation. In this paper we describe the main vegetation types of the area (excluding closed forest vegetation) and relate their patterns of distribution to the former use of the ranch for cattle. The study area comprised the former ranch and parts of the adjacent Saadani Game Reserve, which had not been grazed by cattle for many years and had never been used for large-scale ranching. Following field surveys, 15 distinct types of grassland and bush vegetation were defined and a vegetation map was created using a Landsat TM satellite image. A multispectral classification using the maximum likelihood algorithm gave good results and enabled all 15 vegetation types to be distinguished on the map. Two main spatial trends were detected in the vegetation. One was a large-scale decrease in the cover of bushland from the most intensively used parts of the ranch through more extensively used areas to the game reserve; this trend was attributed to differences in management history as well as to climatic and topographic factors. A second trend was a radial vegetation pattern associated with the enclosures where cattle were herded at night. Extensive amounts of three bushland types [dominated by (i) Acacia zanzibarica, (ii) Dichrostachys cinerea, Acacia nilotica or Acacia mellifera and (iii) Terminalia spinosa] occurred in a zone between 300m and 2 500m from the paddocks, with a peak in bush density at about 900m (mean value for 18 paddocks). In contrast, bushland dominated by Hyphaene compressa was scarce close to the paddocks and became more abundant with distance. There was also a radial trend in the grassland communities: close to the paddocks there was short grass vegetation containing many ruderals and invasive weedy species, while the tall grassland types with species such as Hyperthelia dissoluta and Cymbopogon caesius occurred further away in the areas less affected by cattle. The intensive modern livestock ranching as practised on Mkwaja Ranch proved to be unsustainable both economically and ecologically. In the end, the biggest problem faced by the ranch managers was not controlling disease, as had originally been feared, but preventing the spread of bush on pasture land. The results of our study demonstrate just how severe the problem of bush encroachment was, especially in areas close to paddocks. An important lesson for management is that grazing patterns need to be taken into consideration when determining the sustainable stocking rate for an area. To reduce the risk of bush encroachment in grazing systems with focal points such as paddocks or watering points, stocking rates need to be lower than in systems with a more uniform grazing distribution.