African trypanosomiasis, the parasitic
disease caused by trypanosomes transmitted by tsetse flies
to people and their livestock throughout much of sub-Saharan
Africa, is widely recognised as having had a major impact
on the development of the continent, in particular on the
distribution of its livestock and, sometimes, its human, populations.
Today it continues to cause epidemics in human populations,
where the disease is always fatal if left untreated, and to
leach away the resources of Africa’s livestock keepers,
obliging them to spend substantial sums on trypanocides to
prevent or treat the disease, while still lowering livestock
productivity, increasing their death rates and limiting the
use of animal traction. Thus, like other widespread chronic
diseases of livestock and people, trypanosomiasis contributes
substantially to the perpetuation of poverty.
The Pan-African Tsetse and Trypanosomiasis Eradication Campaign
(PATTEC) has mobilised support from African leaders as well
as substantial funding, which may provide the continent with
a window of opportunity to intervene effectively to control
the disease. But only if PATTEC’s initial programmes
are seen to be successful – in terms of the areas targeted,
the goals set, and cost-effectiveness – will governments,
donors and livestock keepers invest in further tsetse control
rather than continue to rely on trypanocides. Thus informed
decision-making is particularly crucial at this time.
Effective control of trypanosomiasis involves applying a
range of measures:
- control of Human African Trypanosomiasis (HAT) by finding
and treating patients with drugs, supported by vector control
and treatment of livestock with trypanocides, where these
animals are important reservoir hosts;
- treatment and prevention of livestock trypanosomiasis
using trypanocides, focussing on cows, traction animals
and protecting pastoralist herds moving through high tsetse
- suppression of tsetse populations to reduce transmission
rates in areas where trypanosomiasis seriously affects human
health and/or livestock productivity;
- creation of large tsetse-free zones in areas where the
impact of trypanosomiasis is serious, tsetse populations
are relatively isolated, and elimination is feasible.
This last option is currently the main focus of PATTEC activities,
with proposals to eliminate tsetse from 200,000 sq km across
six countries. This brief incorporates the findings of a study
to evaluate the comparative costs of eliminating tsetse in
southern Uganda using a variety of methods.
A wide range of techniques for reducing or eliminating tsetse
populations have been developed and deployed. The four approaches
described below are those currently most widely recommended.
Numerous and extensive studies have shown that the insecticide
levels used in each of these do not have detrimental long
term environmental effects.
Traps and Targets
Traps and targets are structures, usually less than 2 cubic
metres in size, made from black or blue cloth and metal or
wooden rods, which attract tsetse flies visually and may also
be baited with natural and/or artificial attractants to improve
their efficacy. Flies either pick up a lethal dose of insecticide
from the insecticide-impregnated cloth or are lured into a
cage where they are trapped. The main tsetse species present
in the study area in Uganda is Glossina fuscipes.
Currently, there are no effective attractants for this species
and so trap densities of 10 per sq km are recommended, rather
than the 4 odour-baited traps per sq km used against the other
fly in the area, G. pallidipes. At these densities the respective
costs for elimination come to US$ 920 and US$ 500 per sq km.
Insecticide-Treated Cattle (ITC)
Where cattle are present, they themselves can be treated with
insecticide to reduce the fly population. Farmers are often
keen to ‘protect’ their herds in this way, with
the additional benefits of controlling ticks and other nuisance
and biting flies, and application using a spray is very cost-effective.
Costs vary according to method of application, amount of insecticide
used and number of cattle treated per sq km: US$ 240 for the
usual 4 cattle per sq km using sprays, US$ 270 per sq km if
8 animals per sq km are treated in this way.
Aerial Spraying - Sequential Aerosol Technique (SAT)
This approach is based on spraying an area with an insecticide
from a fixed-wing aircraft, five times at set intervals. The
first spray is designed to kill all adult tsetse in the area,
thus instantly removing virtually all vectors. Four subsequent
sprays kill tsetse as they emerge from puparia buried in the
ground. This technique works well on a large scale and is
the most rapid of the techniques, achieving elimination in
as little as two months, costing US$ 590 per sq km.
Sterile Insect Technique (SIT)
Releasing sterile males into a population reduces overall
fertility and hence the growth of a tsetse population. Fly
numbers must first be suppressed to reduce the required number
of costly sterile males and to avoid greatly increasing the
number of viable vectors of the disease in circulation. The
costs of SIT are thus necessarily additional to those of the
suppression technique used and its use is usually envisaged
in situations where other techniques cannot achieve elimination.
Overall costs range from US$ 1,010 if suppression is done
using ITC to US$ 1,300 per sq km if SAT is used for suppression.
While the cost differentials and the calculations involved
are relatively straightforward, information about the effectiveness
of the various techniques, under different conditions, against
different tsetse species and applied on different scales,
is still sometimes lacking. Major differences in the costs,
time scales and logistical constraints of different techniques
might suggest an obvious ‘best bet’ for a particular
intervention. However, it seems likely that for area-wide
operations, more than one technique will be necessary: insecticide-treated
cattle may be cheap but cannot be used where cattle are absent;
aerial spraying may be fast but is impossible in broken terrain
and cannot prevent reinvasion. This is especially true of
those many areas where tsetse populations are not isolated,
so it will usually be necessary to use traps, targets or ITC
to act as barriers to reinvasion.
Three major recommendations have emerged from this work.
- From the entomological point of view, although much has
been published on the effectiveness of the different techniques,
overall guidelines for decision-makers are lacking. It is
recommended that the various experts work towards achieving
a consensus on which technique or combination of techniques
is best adapted for which situation, defining their limitations
and establishing clear entomological guidelines in
a single document. PAAT, the Programme Against African Trypanosomiasis,
combines the expertise of FAO, AU-IBAR, IAEA and WHO, and
constitutes an international platform to provide guidance
on tsetse and trypanosomiasis intervention policies and
- To support this, there is also a need to study former
tsetse control projects paying special attention to the
extent to which project scale, reinvasion pressure and organisational
sustainability contributed to the ultimate outcomes. A consensus
is also needed on these logistical / organisational
factors in order to inform decision-making in this field.
- Lastly, as this study has confirmed, the cost differentials
among the different techniques are so substantial that economic
considerations must be included among the criteria for choice
of technique, especially given the multiple demands on financial
resources for such initiatives, which are working towards
the over-arching goal of poverty alleviation.