Integrated malaria vector control in different agro-ecosystems in western Kenya

190 Pages·2009·6.4 MB·English

Integrated malaria vector control in
different agro-ecosystems
in western Kenya

Susan S. Imbahale
Thesis committee

Thesis supervisors

Prof. dr. ir. Willem Takken
Personal chair at the Laboratory of Entomology, Wageningen University

Prof. dr. Marcel Dicke
Professor of Entomology, Wageningen University

Thesis co-supervisor

Dr. ir. Ron J.A. van Lammeren
Associate professor at the Laboratory of Geo-information science and remote sensing,
Wageningen University

Other members
Prof. dr. ir. Johannes S.C. Wiskerke Wageningen University
Dr.ir. Leo A.J. Nagelkerke Wageningen University
Prof. dr. Ellen van Donk Netherlands Institute of Ecology, Maarssen
Prof. dr. Robert W. Sauerwein Radboud University Nijmegen
Prof. dr. Ken E. Giller Wageningen University

This research was conducted under the auspices of the C.T. de Wit Graduate
School for Production Ecology & Resource Conservation
Susan S. Imbahale

Integrated malaria vector control in
different agro-ecosystems in western
Kenya

Thesis
submitted in partial fulfilment of the requirements for the degree of doctor
at Wageningen University
by the authority of the Rector Magnificus
Prof. dr. M.J. Kropff,
in the presence of the
Thesis Committee appointed by the Doctorate Board
to be defended in public
on Thursday 29 October 2009
at 11 AM in the Aula.
Imbahale S.S. (2009)

Integrated malaria vector control in different agro-ecosystems in western Kenya

PhD-thesis, Wageningen University – with references – with summary in Dutch

ISBN 978-90-8585-475-3
To the Imbahale’s (Alex, Evelyne, Nancy, Ann, Ruth and Lindah)
and the future generations.

Abstract

Malaria is a complex disease and its transmission is a function of the
interaction between the Anopheles mosquito vector, the Plasmodium
parasite, the hosts and the environment. Malaria control has mainly tar-
geted the Plasmodium parasite or the adult anopheline mosquitoes.
However, development of resistant parasites and mosquito vectors re-
quires the development of other strategies, such as larval control, which
can be integrated in the current control programmes. To develop a lar-
val control programme, the local vector species and their breeding char-
acteristics need to be known.

This thesis describes the results of a study on mosquito ecology, with
an emphasis on malaria vectors in different agricultural settings within
two highland sites (Fort Ternan and Lunyerere) and a peri-urban area
(Nyalenda) in western Kenya, and the development of practical and ef-
fective mosquito larval control strategies. To provide information about
the ecology of local vectors, a longitudinal two-year study on the popu-
lation dynamics and breeding characteristics of local mosquito species
and malaria prevalence was undertaken in the respective study sites. In
addition, community perception and knowledge on malaria, causes of
malaria and the control of mosquito vectors were established through a
questionnaire. This information allowed for the development of small-
scale mosquito larval control strategies combining source reduction, en-
vironmental manipulation through provision of shade and biological con-
trol using predatory fish (Gambusia affinis) and application of the bio-
larvicide, Bacillus thuringiensis var israelensis (Bti).

The main malaria vector species, Anopheles gambiae Giles sensu stricto
and An. arabiensis Patton, were both present in all sites as larvae, while
An. funestus Giles was only recorded in the highland villages. The ma-
jority (86%) of mosquito breeding sites were a result of human activi-
ties. Anopheles arabiensis was the main vector species in Nyalenda,
Anopheles gambiae s.s. was dominant in Lunyerere while An. funestus
was common in Fort Ternan. Lunyerere had the highest percentage
(12.5%) of adult indoor resting An. arabiensis mosquitoes ever re-
corded in the western Kenyan highlands. Fort Ternan had the highest
percentage (71%) of larval An. arabiensis ever recorded at such high
altitude. Plasmodium falciparum, the main malaria parasite in the re-
gion, was present in the schoolchildren cohort examined and no signifi-
cant differences in malaria prevalence were observed among the study
sites.The inhabitants of the respective communities regarded malaria as
a burden and they expressed a willingness to take part in mosquito con-
trol, although they did not know how this could be done. A pilot study of
larval control strategies conducted in Nyalenda demonstrated the feasi-
bility of environmental and biological control methods
in man-made, mostly agricultural, mosquito habitats. The larval control
strategies that were applied in the highland villages led to complete
elimination of both early and late instar mosquito populations and com-
pared well with the effects of Bti application.

The results suggest that the larval control strategies developed in this
study will contribute significantly to a reduction in adult mosquitoes and
hence, malaria transmission. Larval control strategies need to be devel-
oped that take into account the breeding habits of the local vectors as
well as the suitability of habitats for a given control strategy. An inte-
grated approach using various larval control strategies that are locally
available, can easily be adopted by the communities concerned. Com-
munity involvement in disease control will lead to knowledge on how
the peoples’ activities affect their health and this can empower them to
take charge of their health.
Abstract 7

Chapter 1 General introduction 11

Chapter 2 Farming systems, water management and malaria mosque 21
toes in Africa

Chapter 3 A longitudinal study on the ecology of aquatic stages of
35
malaria mosquitoes in distinct geographical and environ-

mental settings in western Kenya

57
Chapter 4 Dynamics of malaria transmission in different agricultural

settings in western Kenya

Chapter 5 Community perception of malaria in areas having different 77
transmission levels in western Kenya

Chapter 6 Strategies of controlling malaria mosquito larvae using en- 103
vironmental management and biological control: a case

study of Nyalenda, western Kenya

123
Chapter 7 Integrated control of malaria mosquito larvae in two high-

land villages in western Kenya.

143
Chapter 8 Summarizing discussion

152
References

173
Nederlandse samenvatting (Dutch summary)

177
Acknowledgements (Dankwoord)

181
Curriculum Vitae

183
List of publications

185
Education statement

187
Appendix: Supplemental figure Chapter 3