Scientific bulletin 320 - June 2009
© IRD-CIRAD/ J. Janelle
and animals alike in
Africa. True to its name,
it disturbs the sleep
cycle: the patient sleeps
during the day and stays
awake at night. Sensory
disturbance, motor
coordination anomalies
and mental confusion
develop. The whole
central nervous system
is subsequently affected,
triggering neurological
disorders. Left untreated,
sleeping sickness is fatal.
This devastating disease
had been brought under
control in the 1960s, but it
has been surging up again
over the past 15 years.
WHO estimates at 300 000
the number of new human
cases each year. There is
no hope of a vaccine in
the medium term and the
few treatments currently
available are highly toxic.
The culprits are tsetse
flies and the parasite they
transmit with their bite.
Yet, during the course
of the 20th Century, the
number of flies fell and
their geographical range
regressed. IRD researchers
and their partners1 have
shown that surging
population growth,
economic development
and climate change in
West Africa have strongly
modified and largely
destroyed their natural
habitat, the savannah.
Does this imply hope of a
regression of the disease?
Such an assumption
would be leaving aside the
ability of certain species to
adapt to urban conditions,
and these are the most
dangerous for humans.
They are now encroaching
into towns and cities,
raising the risk of epidemic
foci in urban areas.
Sleeping sickness:
tsetse flies counterattack in urban areas
© IRD / Philippe Solano
leeping sickness is
S
a parasitic infection
which affects humans
Trapping tsetse flies on the banks of the River Comoe, southern Burkina Faso.
At the beginning of the 20th Century,
humans used to flee from tsetse, flies
of the Glossina genus, to protect themselves and spare their livestock. When
they bite, these insects transmit the parasite responsible for sleeping sickness,
Trypanosoma brucei, which invades first
the host’s blood then its nervous system, causing an inversion of the sleep
cycle. This disturbance is accompanied
by sensorial dysfunction, the motor function anomalies, mental confusion and
neurological disorders. If the disease is
left untreated, the victim falls into a coma
and eventually dies.
The roles have now been reversed:
human settlement patterns determine tsetse distribution. Population
growth, economic development and
climate changes that have occurred
in West Africa over the past 100 years
have profoundly changed human
settlement and landscapes. These intense modifications have had consequences for the tsetse, completely dependent on animal and human blood for
their food. The flies have therefore had
to adapt.
Tsetse are fewer …
The insects have thus seen their numbers decreased and their overall distribution range in West Africa retract. Certain
species have completely disappeared
from the savannah, their natural habitat.
The role of humans is undeniable. IRD
researchers and their partners1 analysed
aerial photographs taken between 1952
and 2007 in the Boucle de Mouhoun region, in the west of Burkina Faso, where
the human disease has now been eradicated. The series of photos showed
degradation of the landscape, such as
destruction of the vegetation cover, and
disappearance of the wild fauna. Increase in human population densities,
quadrupled in 50 years in West Africa,
and displacement of populations generated by climatic anomalies (drought in the
1970s, floods and so on) have caused
striking changes and deterioration of
the vector’s ecological niches. Climate
change has also influenced the tsetse
distribution range more directly. Reduction in rainfall has resulted in a 200 km
southward shift of the northern limit of the
flies’ range in 100 years, to the modified
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You can find the IRD photos concerning this bulletin, copyright free for the press, on www.ird.fr/indigo
Philippe SOLANO,
chercheur à l’IRD
UMR Interactions
hôte-vecteur-parasite
dans les infections par des
Trypanosomatidae
(IRD/CIRAD)
Address:
CIRDES Bobo Dioulasso
01 BP 454
Bobo Dioulasso
Burkina Faso
Tél. : (226) 20 98 51 94
philippe.solano@ird.fr
solano@ird.bf
REFERENCES:
Courtin F., Sidibé I.,
Rouamba J., Jamonneau
V., Gouro A., Solano P.
Impacts des évolutions
démographiques et
climatiques sur la
répartition spatiale des
hommes, des tsé-tsé et
des trypanosomoses en
Afrique de l’Ouest. Parasite
- Journal de la Société
Française de Parasitologie,
16 (1), p. 3-10, 2009
KEY WORDS:
Sleeping sickness, tsetse fly,
population growth, climate,
West Africa
with the vector, and are therefore more
vulnerable to trypanosomes, into endemic zones. Moreover, political instability
impedes the implementation of effective
durable medical intervention plans or
vector control strategies.
Sleeping sickness has consequently undergone profound epidemiological modifications owing to the combination of the
past century’s population and climatic
changes. Tsetse flies are less numerous
and are geographically restricted to a
smaller range, yet they are just as densely concentrated, more particularly so in
the large urban areas. Linking up of all
the strands of knowledge (on population, ecology, climate, entomology,
health) will enable scientists to formulate possible epidemic/disease eradication scenarios and to determine the
priority areas for medical intervention
and vector control in the future. This
multidisciplinary approach can be extended to other vector-borne diseases
such as malaria or chikungunya.
Gaëlle Courcoux - DIC
Translation - Nicholas Flay
1. This research work was conducted jointly
with researchers from the Centre International de Recherche - Développement sur l’Élevage en zone Subhumide (CIRDES) and the
Centre Muraz, Bobo-Dioulasso in Burkina
Faso, and the West African countries’ national programmes for HAT (human African
trypanosomiasis) control.
2. Tsetse flies inhabit mainly the most humid
areas of the savannah such as river valleys.
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Sleeping sickness screening survey in Burkina Faso.
© IRD
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boundary of the more humid area. The
result: the disease has disappeared from
the savannah but has appeared in zones
of forest and mangrove further south.
Another factor is the construction of hydrological schemes in the 1980s, which
has steadily reduced fly-human contacts2,
as people were no longer obliged to go to
the river to fetch their water, and allowed
a regression of the disease to take place.
… but more dangerous.
With 617 million inhabitants predicted in
2050 in a context of climate variability,
will the flies disappear from West Africa?
Unfortunately, although some groups of
tsetse are only poorly resistant to anthropogenic pressure, others adapt very
well to strong human population densities. This is especially the case of the
most dangerous tsetse for humans, flies
of the palpalis group, which have successfully adapted their feeding patterns
to urban conditions. Great numbers of
these tsetse live in most cities of West
Africa and indeed of central Africa such
as Kinshasa in the Democratic Republic
of Congo, Abidjan in the Ivory Coast and
Dakar in Senegal.
The impact of conflicts.
Added to the insecurity associated with
the fight for economic, land and hydrological resources stemming from high
population growth is the multiplication of
recent conflicts such as those in Liberia,
Sierra Leone or Ivory Coast which aggravate the phenomenon of intense mobility
of the West African population. These migrations increase the risks of spreading
of sleeping sickness and bring populations who have never been in contact
© IRD-CIRAD/ Fabrice Courtin
Scientific bulletin 320 - June 2009
For further information
IRD sleeping sickness control campaign.
Gaëlle Courcoux, coordinator
Délégation à l’information et à la communication
Tél. : +33 (0)4 91 99 94 90 - fax : +33 (0)4 91 99 92 28 - fichesactu@ird.fr