Tsetse are large biting flies found in areas of woody scrub and bush across much of tropical Africa. Because they are vectors of trypanosome parasites that cause sleeping sickness in humans and nagana in domesticated animals, their presence makes large tracks of land unsuitable for rearing cattle or farming.
Vector control is a major facet of programmes aimed at reducing the transmission of sleeping sickness and nagana. However, a major problem encountered by tsetse fly control campaigns is the invasion of flies from areas outside the boundary of the control zone when a project ends.
Tsetse control in Burkina Faso
Along with several other countries in sub-Saharan Africa, many areas of Burkina Faso are plagued by tsetse flies and the trypanosome parasites that they transmit. Previous intensive control programmes, conducted in the 1980s and 1990s, failed. This was because local communities did not keep up the control efforts after the projects ended and tsetse flies from surrounding areas invaded the controlled zones, bringing trypanosomiasis back with them.
In the second decade of this century control of this scourge has again been attempted.
A 21st century programme: lessons learnt
Between 2009 and 2013, a multifaceted programme was conducted as part of the Pan African Tsetse and Trypanosomosis Eradication Campaign (PATTEC). This followed a survey to determine tsetse distribution in the target area. The aim was to eliminate tsetse flies from a 40,000 km2 area.
The programme was based around the use of insecticides applied to targets, traps and cattle and ground and arial spraying. In addition, mass treatment of local livestock with trypanocides was conducted. Crucially, the programme aimed to benefit from past mistakes by involving local communities.
Lassané Percoma and co-workers recently reported the results of a two year study aimed at assessing the success of this project.
The regions where the project was conducted are largely rural and are crossed by the Mouhoun River and its tributaries, which provide the riverine habitat that tsetse flies favour. Even before the control methods began, local communities were kept informed. Members of the villages were chosen to act as auxiliaries for the control teams as base-line surveys were conducted.
Tsetse flies are attracted to slow moving, dark surfaces. This behaviour forms the basis of the success of tsetse targets.
Over 42,000 commercially sourced targets, made of blue and black material impregnated with the insecticide deltamethrine, were used. These were set up by the village auxiliaries along the river banks in the areas shown to be infested with flies during the preliminary survey.
To assess the effectiveness of the programme, bimonthly checks were made using insecticide impregnated tsetse traps.
To prevent reinvasion from beyond the project, barriers made of targets and traps were erected at the boundaries of the river and tributaries. Local supervisors were also used to maintain these traps and targets.
Arial spraying with deltamethrine was also deployed in this barrier zone and further along the river in Ghana, in conjunction with a counterpart study there. Ground spraying was also performed in this area before the rainy seasons.
Involvement of domesticated animals
Animals can act as live bait for tsetse flies. An insecticide was applied to the skin of cattle, sheep and donkeys in villages near the tsetse infested rivers. As the local cattle could be infected with trypanosomes they were treated with a trypanocide as part of the project. Cattle in a sentinel herd in 11 villages were checked for the presence of parasites bimonthly. Initially this was all provided free but after the first year villages paid for the services of veterinarians.
After three months, the apparent density of tsetse flies per trap per day had dropped by 95% and in 2013 flies were only captured in 29% of the original infested sites. Control was least successful in some Western areas.
The authors of this paper stress the importance of the engagement and contribution of local people. In all 75 tsetse control committees set up in the agro-pastoral areas and more than 500 village auxiliaries involved, together with 955 agents from the Ministry of Resources of Animals and Halieutic. They point out that the area with the least control success was the one with least community involvement and where many of the traps were removed by local people.
The use of targets which require regular maintenance and kept tsetse density very low for 4 years is a control method ideally suited to community participation. Ground spraying is another control method that can be performed by local staff, whereas aerial spraying requires highly trained operatives.
Lassané Percoma and colleagues make the very important point that, to achieve sustainable control, the commitment of local communities must be reinforced with the ongoing provision of impregnated targets to local committees and regular monitoring linked to other ongoing activities that involve livestock.
As this project demonstrates, the involvement and commitment of communities in endemic countries to local vector control programmes must be an essential component of programmes for the eradication of insect transmitted diseases.