AREA-WIDE PAN AFRICAN TSETSE AND TRYPANOSOMOSIS ERADICATION CAMPAIGN FOR THE CENTRAL SOUTH OF MOUNT KENYA BELT-PROSPECTS AND CHALLENGES

CAMPAGNE PANAFRICAINE A GRANDE ECHELLE D’ERADICATION DES TSETSE ET DE LA TRYPANOSOMOSE DANS LA ZONE ENFESTEE PAR LES TSETSE DU CENTRE-SUD DU MONT KENYA – PERSPECTIVES ET DEFIS

Kenya Agricultural Research Institute, Trypanosomiasis Research Center, P.O Box 362, Kikuyu, 00902

            La zone infestée par les tsétsé du Centre-Sud du Mont Kenya a été identifiée et ciblée pour l’éradication dans le cadre de la Campagne à grande échelle d’éradication des tsétsé et de la trypanosomose (PATTEC). Des enquêtes préliminaires ont été menées dans tous les onze districts de la zone pour recueillir des informations sur la densité et la répartition des tsétsé, la prévalence de la trypanosomose, la végétation, l’agriculture, le potentiel de développement de l’élevage et bien d’autres paramètres majeurs. Les résultats des enquêtes semblent indiquer un recul progressif de la zone infestée par les tsétsé vers les zones de conservation de Mwea et de Meru, en raison de l’accroissement des activités humaines qui ont détruit les anciens habitats des tsétsé. La menace des tsétsé et de la trypanosomose semble donc peser sur les communautés vivant dans les environs des zones de conservation. Contrairement à la carte de Ford et Katondo publiée en 1967, qui ne montrait qu’une seule espèce de mouches, la récente enquête a révélé la présence de trois espèces de mouches tsétsé, à savoir : G. pallidipes, G. brevipalis et G. longipennis. Les densités de tsétsé variaient d’un district abritant les zones de conservation à un autre, et étaient beaucoup plus élevées dans les districts de Meru Nord et d’Isiolo ; une variation qui pourrait être attribuée aux différences entre les types de végétation et de couvert végétal, entre les populations de faune et entre les niveaux de l’activité humaine. De même, les taux de prévalence de la trypanosomose variaient selon la densité des tsétsé et le système d’exploitation agricole. Le confinement apparent des tsétsé dans les zones de conservation offre une excellente opportunité pour l’éradication. Cependant, la conservation de la riche biodiversité pourrait constituer le plus important défi à relever par le programme d’éradication. Un modèle intégré de déclaration des zones exemptes d’infestation de tsétsé devra être conçu pour servir d’appui à la campagne d’éradication.

            The central south of Mt. Kenya tsetse belt, one of the five major tsetse belts in the Kenya, has been identified and targeted for possible eradication by the Government of Kenya as part of the Pan African Tsetse and Trypanosomosis eradication campaign (PATTEC). Preliminary surveys were undertaken in twelve administrative districts that fall within the belt to establish the current status of tsetse and trypanosomosis. Data on tsetse density and species, and trypanosomosis prevalence was collected using odour-baited traps, examination of blood for parasites by the buffy coat method. Tsetse infestation by three species G.pallidipes, G.brevipalpis and G.longipennis was observed in eight districts encompassing the Mwea and Meru conservation areas. The fly/trap/day range was 0.75 - 45.5 and was high in Meru North and Mbeere districts. Trypanosomosis prevalence, range 0.4 - 3.19 was recorded in eight districts and followed tsetse infestation. Infections were mainly due to Trypanosoma congolense and T.vivax. The results of the survey suggest a gradual roll back of the belt into tsetse Mwea and Meru conservation areas due to increased human settlement and agricultural activities in most areas that may have reduced tsetse habitants causing low vector density and alterations in distribution. Tsetse and trypanosomosis thus appears to affect communities living close to conservation areas. There still remains a need for intense surveys using more sensitive tools to establish true absence of flies in areas where none were detected and in areas where flies were detected, further surveys to establish tsetse distribution, and the feasibility, environmental impact and cost-benefit analysis of undertaking an eradication program.

Introduction

            African animal trypanosomosis is considered a major constraint to livestock productivity in sub-Saharan Africa (SSA) (Leak et al., 1988) and has profound effects on rural development over vast areas (Holmes, 1997). It is estimated that tsetse flies are distributed over approximately 11 million km2 of Africa (Jordan, 1986), which is about 37% of the continent (FAO/WHO/OIE, 1982). Presently, out of the estimated 172 million head of cattle, approximately 44.7 million are at risk of trypanosomosis (Gilbert et al., 2001). The economic losses attributed to animal African trypanosomosis are due to decreased meat and milk production as a result of mortality, morbidity and infertility. When the impact of crop productivity due to reduced animal draught power and manure is considered, the true economic losses could be much higher (Budd, 1999).

            In Kenya, it is estimated that 25% of the country including 60% of the rangelands with pasture and water suitable for raising cattle is infested with various species of tsetse flies. Tsetse and trypanosomosis distribution in the country follows distinct and isolated belts that are either found within the countries boundaries or overlapping to neighbouring Uganda, Tanzania and Somalia. These tsetse belts are: (i) arid and semi arid lands north of Mt. Kenya tsetse belt; (ii) central Kenya tsetse belt; (iii) the north rift tsetse belt; (iv) the south rift tsetse belt  (Lake Bogoria belt); (v) western Kenya & Lake Victoria tsetse belt; (vi) the Transmara-Narok-Kajiado tsetse belt; and,(vii) the coastal tsetse belt.

            Following the recent establishment of the Pan African Tsetse and Trypanosomosis Eradication Campaign (PATTEC), countries in the AU that are tsetse infested have been developing programmes and implementation schedules to initiate tsetse eradication projects, with support from a number of international organizations. In Kenya, Trypanosomosis Research Center at KARI and the Department of Veterinary Services are jointly spearheading these efforts under the banner of ‘Integrated Area Wide Tsetse and Trypanosomosis Management’, with individual projects addressing pockets of isolated tsetse belts. One of the belts targeted for possible eradication under the initiative is the central belt south of Mt. Kenya.

            The belt is located in central Kenya and extends from Meru North District in the north to Machakos District in the south through eight districts namely, Meru North, Meru South, Meru Central, Tharaka, Mbeere, Thika, Maragwa, Mwingi and Machakos. It is physically isolated from the central belt north of Mt. Kenya by the Nyambene hills and geographically from the coastal belt by environmental factors. The main features within the belt are the Mwea national reserve, Meru conservation area and Tana River, which runs on the southeast border of the belt.

            In view of the importance of tsetse and trypanosomosis problem in Kenya and in line with the objectives of PATTEC initiative, preliminary surveys were undertaken in twelve administrative districts that fall within the belt and around the Meru conservation area. The objective of the survey was to establish the status of tsetse and trypanosomosis within the belt as a prelude to eradication.

Materials and methods

Study area

Cross-sectional survey was undertaken in Meru North, Meru South, Meru Central, Tharaka, Thika, Maragwa, Mbeere, Machakos, Isiolo, Tana River, Garissa and Mwingi districts between June 2003 and November 2004 (see map).

Data collection

Entomological data

To determine the apparent tsetse densities, odour-baited biconical traps were deployed at various sampling points where tsetse infestation was suspected. Selection of trapping sites was based on vegetation cover, proximity to drainage systems and areas with human/animal activities e.g., grazing areas and watering sites. All the traps were baited with acetone and phenol sachets and set out at forty-eight-hours. Flies caught were identified, classified, sexed, counted and recorded.

Parasitological data

            Trypanosome infection in animals, predominantly cattle was detected using the BCT (Murray et al., 1977). Briefly, blood from the jugular vein was collected in 5 ml heparinised vacutainer tubes , transfered into heparinized capillary tubes and processed for determination of packed cell volume (PCV) and examination of trypanosome, their species and level of parasitaemia.. All animals that were found to be infected with trypanosomes and those with PCV value of less than 25 were treated with diminazene aceturate at a dose rate of 3.5mg/kg body weight intramuscularly. Also collected was secondary data on disease incidence from district animal health records. All trap positions and animal sampling sites were geo-referenced.

Results

            The findings on tsetse density and species, and trypanosomosis prevalence and species in the twelve districts within the central belt south of Mt.Kenya are shown in Tables 1 and 2.

            Tsetse flies were detected in eight out of twelve districts surveyed. The numbers were generally low except in Isiolo, Meru north and Mbeere districts, which border the Mwea, Meru and Mwea conservation areas. Three species, G.pallidipes, G.brevipalpis and G.longipennis, were detected with G.pallidipes being predominant. The low numbers of flies detected in Meru North district in July 2003 was reported to be due to a tsetse control program initiated in the park by the Kenya Wildlife Services. According to the farmers, the program had greatly reduced the number of flies in the surrounding farmlands. In Meru central district, the low numbers were attributed to increased cotton growing that had resulted in frequent use of pyrethroid insecticide, a chemical control agent insects including tsetse flies. In all other districts farmers reported a general decline of fly numbers that they attributed to the destruction of tsetse habitants that had occurred over the years. The trypanosome infection due to Trypanosoma congolense and T.vivax in animals were detected all the nine districts with tsetse fly infestation. The prevalence of infection was generally low. In all districts where tsetse was detected, the disease was reported in the annual animal health records. Almost all the cases were unconfirmed due to lack of laboratory facilities

Table 1: Tsetse densities and species in twelve districts surveyed between 2001 and 2004

Discussion

            Results of preliminary surveys have confirmed the presence of tsetse flies and trypanosome infection in animals in eight districts within the central belt south Mt. Kenya and around the Meru conservation area. The pattern of infestation appears to suggest a gradual roll back of the belt into conservation areas. This could be attributed to increased human settlement and agricultural activity in most areas.

            Thus, tsetse and trypanosomosis appears to afflict communities inhabiting areas close to conservation areas. Environmental alterations resulting from land use changes such as settlements and agricultural activities may have brought about reduced tsetse habitats causing low vector density and its distribution. In particular, crop farming/agricultural activities such as cotton and horticulture require heavy usage of pyrethroids, which in essence reduces insects including tsetse flies

Table 2: Trypanosomosis prevalence and species in Twelve districts surveyed
               Between 2001 and 2004

References

Budd, L. (1999). Tsetse and Trypanosomosis Research and development from 1980. an economic analysis. DFID commissioned report. DFID,UK

FAO/WHO/OIE (1982). Animal Health Year Book. V. Kuoba (ed). Food and Agricultural Organization, Rome Italy.

Gilbert, M., Jenner, C., Pender, J., Rogers, D., Slingenbergh, J. and Wint, W. (2001). The development and use of the Programme Against African Trypanosomosis Information System (PAAT-IS). Newsletter on Integrated Control of Pathogenic Trypanosomes and their Vectors (ICPTV). No.3.pp. 10-12

Holmes, P.H. (1997). New opportunities for the diagnosis and control of animal diseases in the tropics. Trans.R.Soc.Trop.Med.Hyg. 85:163-167

Leak, S.G.A. (1999). Tsetse biology and ecology: their role in the epidemiology and control of trypanosomosis. CABI publishing, Wallington, Oxon, UK

Murray, M., Murray, P.K. and McIntyre, W.I. (1977). An improved technique for diagnosis of African trypanosomosis. Trans.R.Soc.Trop.Med.Hyg. 71:325-326