1.2 Outline of official arrangements
2.1 Pre-control survey in the Kwando/Mamili area
2.3 Trypanosomiasis surveillance
2.4 Implementation of target operations
3.3 Trypanosomiasis surveillance and sentinel herds
3.4 Trypanosomiasis control in Katima Mulilo
3.5 Extension and community support
Namibia has a long history of tsetse control, dating back to the early 1960s, when the ground spraying technique was applied. However, the success of this operation was jeopardized by the continual invasion of tsetse from neighbouring countries, a situation which was exacerbated by the geographical location of the Caprivi. Tsetse flies are confined to the Caprivi strip in Namibia, and the country is infested by a single species, Glossina morsitans centralis.
Historically, tsetse is known to have been eliminated from the Caprivi by 1912 following the rinderpest panzootic epidemic in l896 which destroyed game and cattle. The tsetse population reestablished itself in 1937, spreading northwards from Botswana along the Kwando and Mashi drainages. This reinfestation reduced cattle production from 20 000 in 1950 to 9 000 in 1958. Bovine trypanosomiasis once again presented a major constraint, particularly after the suspension of ground spraying operations in 1988.
It was against this background that the Government of the Republic of Namibia sought financial assistance and technical guidance in the use of odour-baited and insecticide-treated targets from the EU-funded Regional Tsetse and Trypanosomiasis Control Programme (RTTCP). The change from ground spraying to targets was effected for ecological reasons and to facilitate access to donor funding. A trypanosomiasis surveillance programme was initiated in 1991 by the RTTCP, which confirmed the wide distribution of the disease in the Kwando and Katima Mulilo areas.
In response to the Government of Namibia's concern over the growing trypanosomiasis problem, which was presenting a major constraint to land and livestock production, FAO agreed to set up a complementary project, TCP/NAM/2360, Tsetse control to assist livestock production, under its Technical Cooperation Programme. This emergency operation would be followed by a more sustainable EU-funded RTTCP project for Namibia, Angola, Botswana and Zambia.
Project TCP/NAM/2360 was approved in August 1993 and was implemented from May 1994 to November 1995 with an FAO contribution of $US 121 000. The Ministry of Agriculture, Water and Rural Development was designated the government agency responsible for project execution.
The objectives of the project were to:
- undertake an extensive survey to establish the distribution and abundance of tsetse in the Caprivi, in order to determine priority areas for control with targets; and
- reduce the risk of trypanosomiasis in the area immediately to the east of the Kwando and north of Mamili National Park, as well as in the immediate vicinity of Katima Mulilo, by setting up barriers of targets to suppress local tsetse populations and to protect against invasion from neighbouring countries.
The main achievements of the project were the introduction of bait technology for the survey and control of tsetse in Namibia, the training of local staff in the use of the technology and the alleviation of tsetse and trypanosomiasis problems within the settled area in the Caprivi Strip.
The survey operation, which was the initial phase of the project, was undertaken using: - 108 epsilon traps baited with methyl ethyl ketone (MEK) and 1-octen-3-ol; and
- mobile teams equipped with black screens baited with MEK.
MEK was dispensed from 500 ml bottles at the rate of 500 mg/hour and 1-octen-3-ol was dispensed from polythene sachets (300 microns thick and 55 cm2 surface area) at the rate of 0.1 mg/hour. The survey area was subdivided into blocks, with Blocks I and II on the western bank of the Kwando flood plain and Blocks III and IV on the eastern bank. Several other traps were placed on "tree islands" in the flood plain.
The trap survey confirmed the presence of tsetse flies in the entire section along the western bank of the Kwando drainage, between the borders with Angola and Botswana. Trap catches between the two borders confirmed that the fly density was not homogenous in this area, but was highest in the central section between Susuwe Nature Conservation Camp and the ox-bow lake (horseshoe). Tsetse catches from a set of seven traps deployed along the Kombere Molapo indicated that fly density declined from the border with Angola towards the Kwando.
A single tsetse fly was captured in one of the ten traps along the border with Zambia. No flies were captured within the settled area, except at Sangwali, north of Mamili National Park. The ten traps deployed along the main road through Sangwali and Malengalenga did not produce any flies, indicating that flies had not advanced that far north of the National Park.
Two fixed transects (permanent flyrounds) were set up at Susuwe for sampling tsetse. Each of the flyrounds gave an excess of 80 tsetse per traverse. The majority of the catches was male, as expected.
Twenty-five epsilon traps were deployed along the Zambezi river, starting from Fatima in Katima Mulilo as far as Hippo island and along the western edge of the Zambezi Flood Plain to Lusikili. No tsetse flies were caught and the operation was disrupted by the high rate of theft of trap material.
Trap results for the Kwando operation showed a drastic reduction in tsetse catches. By October 1994, three months after the deployment of targets, the trap catches west of the Kwando declined by over 75%. No tsetse were recorded in October and November 1994 in the traps (M1 to M6) along the main invasion route from Angola. A single trap (M7) located near the western edge of the target barrier showed a reduction in tsetse catches.
Similarly, tsetse was reduced on Lupala island and no tsetse flies were recorded near Sangwali villages after the deployment of targets on the island and along the northern boundary of Mamili National Park.
The magnitude of the trypanosomiasis problem east of the Kwando river and at Katima Mulilo was not well known at the start of the project. A total of 52 cases of bovine trypanosomiasis was diagnosed in Eastern Caprivi in 1993, according to a report by the Veterinary Service Department. The disease is reported to have killed nine animals in that year. Recent figures obtained from veterinary records in Katima Mulilo suggested that the situation had further deteriorated, with a total of 45 cases of trypanosomiasis having been diagnosed at Sesheke, Kalubi, Kongola, Choyi and Singalamwe in two months (July and August 1994). The death of 30 cattle was reported in the same period, in the same inspection centres. However, not all these deaths were conclusively demonstrated to be due to trypanosomiasis.
The disease situation was exacerbated by the regular movements of elephants across the flood plain into the settled area, bringing tsetse with them. Elephants and cattle are often observed on "tree islands" on the flood plain in search of water and grazing. It was on these islands that cattle seemed to be acquiring most of the infections.
Farmers reported, at a meeting held with the Technical Assistance Expert (TAE), that they purchased drugs for the treatment of their cattle from either the Department of Veterinary Services or from private commercial outlets. The diagnosis of trypanosomiasis is at present based on clinical signs and accessional examination of stained blood smears. This diagnostic approach is not very reliable and could lead to misdiagnosis, particularly in the presence of other parasites such as liver fluke, which is common in Eastern Caprivi.
The second phase of the project involved the setting up of barriers of targets in strategic positions to suppress the tsetse population and to reduce their invasion into settled areas. Target deployment began in August 1994 and ended in November 1994.
A 5 to 7 km wide band of targets, evenly distributed with a target in each 0.25 km2, was instituted on the western bank of the Kwando. The targets were deployed at 500 m intervals along the 270_ E - W transects. The transects along which the targets were deployed were also 500 m apart. A short 5 km wide barrier was also erected immediately to the east of the Kwando drainage, where some 132 targets were deployed on the eastern bank.
Targets were deployed on Lupala island at the density of 30/1 km2. The targets were placed in parallel transects 250 m apart. Within the transects, the targets were deployed at 200 m intervals. A total of 363 targets was deployed on Lupala island, with 99 others deployed along the northern boundary of Mamili National Park to create a 1 km wide barrier of targets. The barriers at Mamili were erected to restrict tsetse invasion into the settled areas north of the park. The choice of barrier configuration was dictated by the pattern of vegetation in the flood plain.
On the targets (cloth screens mounted on a rotating metal frame) used, only the black section of the blue-black target cloth was treated with a 0.54% suspension concentrate of deltamethrin (Glossinex) at 2,0 g a.i. per target, a dosage sufficient to persist for a year on target cloth. Treatment of the 1 512 targets deployed was carried out in the offices of the Veterinary Services Department in Katima Mulilo. The centralization of target treatment, rather than treatment in the field, is now recommended in order to standardize the treatment.
Targets performed satisfactorily and were reserviced in August 1995, a year after deployment. The following were some of the drawbacks encountered in the use of targets in the Caprivi.
Some targets were damaged by the wind as the basal bar of the frame was too weak to support the all-cloth target used. The sort of frame used was originally designed for the cloth and net type of target. Because the bar is too weak it bends, allowing the cloth to distort in a manner that provides lift in strong wind.
The theft of targets was a major problem near the border with Angola. Thefts were, however, reduced by slitting the targets. This was done in two different ways: either making three or four vertical slits about 80 cm long or many slits about 5 cm long.
The central black panel of some of the targets (about 20%) had faded to brown because the cloth had not been double-dyed. All faded targets were replaced by the supplier company with new cloth that had been double-dyed.
Some of the collector bottles had been distorted by exposure to the intense heat of bushfires. The problem was avoided by increasing the size of clearings around the traps to a radius of about 5 m.
An improved design of funnel produced from a specially designed mould was demonstrated to facilitate better transfer of tsetse from the trap cone into the cage or collector. The old collector model had presented difficulties to staff in setting it up correctly.
The training of the Namibian tsetse control staff constituted an important aspect of the TAE's duties during all the missions undertaken. Training in the use of traps and targets covered the following:
- Setting up of traps and the selection of appropriate trapping sites.
- Use of black screens as mobile baits along permanently marked transects (fixed flyrounds).
- Impregnation of targets with insecticide.
- Drying and packaging of treated targets.
- Erection of targets: where to set up a target, how to fix the vertical shaft, how to attach the cloth to the frame, where to place the odour sachets and acetone bottles and how to clear the area surrounding the target.
- The deployment of targets in grids, the use of the compass and the measurement of distances between targets.
The survey operation demonstrated the presence of tsetse on the western bank of the Kwando drainage at a higher density than on the east.
The capture of a single fly along the border with Zambia indicated that the northwestern corner of Eastern Caprivi was exposed to tsetse invasion from either Zambia or Angola. There was no conclusive evidence on the origin of this fly. This can be discovered only through surveys conducted by Zambia in the National Park that borders Namibia and Angola.
Although only a single tsetse fly was detected by trapping on the eastern bank of the Kwando, the presence of positive cases of trypanosomiasis was a clear indication of the infiltration of tsetse from the western bank across the flood plain. The capability of tsetse to cross the flood plain was confirmed by the capture of tsetse on "tree islands". A similar situation was detected in Mamili National Park, where tsetse flies are present on Nkasa and Lupala islands, and on many other smaller islands. Fly movement across the flood plain was facilitated by the movement of buffalo and elephant between Mamili National Park and the Okavango Delta in Botswana.
The detection of a tsetse density gradient from Angola declining towards the Kwando suggested that tsetse were invading the Kwando area from Angola. The invasion appeared to occur via specific invasion routes where the fly densities were higher than in the surrounding areas.
The search of vehicles travelling through Kongola bridge indicated that few tsetse were being carried to the east by the vehicles. There was therefore no justification for establishing a fly control gate involving the treatment of cars with insecticides.
The post-control surveys showed a drastic reduction in tsetse catches three months after the deployment of targets, resulting in the alleviation of bovine trypanosomiasis in Kwando and north of Mamili National Park. Although the operation was successful, it is realized that the removal of tsetse from the entire region, involving coordinated operations in Namibia and the neighbouring countries, would lead to the long-term goal of total eradication of tsetse from Namibia. Despite the absence of formal trypanosomiasis diagnostic techniques to assess the impact of control measures, local residents and stock owners were convinced that the targets had a satisfactory effect and their cattle are now substantially free of trypanosomiasis.
The management, organization and implementation of the tsetse and trypanosomiasis control programme in Namibia would be enhanced by the establishment of a permanent Tsetse and Trypanosomiasis Control Unit consisting of well-trained staff. The staff engaged in the control unit would operate more effectively if they were not assigned duties in other veterinary disease control programmes. The unit should be provided with adequate operational resources and the necessary logistical support, including transport. If such a unit is not established, the gains made by this programme will soon be lost.
Surveys in the Kwando area demonstrated that the barrier had been effective in suppressing the tsetse population and in intercepting invasion from Angola. An extensive survey programme should be considered to determine the extent of tsetse infestation west of the Kwando.
Surveys at Mamili National Park demonstrated the presence of tsetse throughout the park. It is recommended that Namibia extend the target operation to cover the entire park, to ensure protection of the settled area north of the park against tsetse invasion. In addition, a proposal should be made for Botswana to mount a complementary target operation adjacent to Mamili National Park to reduce cross-border tsetse invasion into the Caprivi.
It is imperative to maintain a continuous tsetse sampling programme throughout the treatment area to monitor the effectiveness of the control programme.
The diagnosis of trypanosomiasis based mainly on clinical signs could lead to misdiagnosis. It is recommended that trypanosomiasis surveillance be organized to include on-site or field-based examination of blood samples, using both parasitological (Buffy coat, thick and thin smears) and serological methods. Improved trypanosomiasis surveillance methods are needed to quantify animal trypanosomiasis and to monitor the effect of target operations in the Caprivi. Target barriers implemented in Kwando and Mamili will not remove any self-sustaining populations of tsetse that are already in the settled area east of the Kwando-Mashi drainage. Sentinel herds of cattle should be maintained to regularly monitor the incidence and prevalence of trypanosomiasis.
No tsetse control measures are recommended in Katima Mulilo. The failure to capture tsetse flies in this area and the detection of only a few cases of trypanosomiasis along the Zambezi river, suggest that the problem is not widespread. No further sampling of tsetse is needed in the near future. Sentinel herds of cattle should be set up and monitored for trypanosomiasis. In addition, all cattle in the area should be regularly inspected and treated with drugs if infected.
The use of prophylactic drugs is not recommended, as this would be more costly than treating infected cattle with curative drugs in view of the low prevalence of the disease. Dipping of cattle with pesticides would also be a more costly option than treating infected cattle, given the current low levels of tsetse infestation. Dipping would become more applicable if the disease incidence continued to increase as a result of a build-up of the tsetse population.
The theft of virtually all the traps deployed along the Zambezi river suggests that traps and targets cannot at present be considered a practical option for tsetse surveys and control in Katima Mulilo. Extension work would be necessary to educate the local community on the use of traps and targets against bovine trypanosomiasis. Finally, Zambia should be urged to mount a supporting operation around Sesheke to reduce cross-border tsetse invasion into Katima Mulilo.
Tsetse and trypanosomiasis control work demands the support and cooperation of the local communities. As in Katima Mulilo, education campaigns should be extended to other trypanosomiasis-affected areas to ensure the success of future target control operations and trypanosomiasis surveillance with sentinel herds. The slitting of targets should be continued to reduce thefts of target cloth.
Although fairly well trained and familiar with the use of baits, Namibian staff still require further technical assistance in the maintenance of traps and targets, to ensure sustainability of the project's achievements.
The permanent solution to the trypanosomiasis problem in the Caprivi requires international cooperation in removing tsetse from all parts of the common flybelt; an EU-funded consultancy study on the feasibility of a regional programme for Namibia, Botswana, Zambia and Angola has already been commissioned.
REPORTS PREPARED DURING THE PROJECT
Extensive surveys to determine pattern of tsetse (Glossina morsitans centralis) distribution in areas adjacent to the Kwando and Mashi Flood Plains in the Caprivi, Namibia. First Mission Report.
The use of odour-baited and insecticide-treated targets to control populations of tsetse (Diptera glossinidae) in the Caprivi, Namibia. Second Mission Report.
Effects of barriers of targets on tsetse distribution and invasion into the west (Kwando) and southwest (Mamili National Park) of Eastern Caprivi, Namibia. Third Mission Report.
An assessment of the performance of target barriers at Kwando and Mamili National Park and monitoring of the target reservicing programme. Fourth Mission Report.
