Chemoecological management of malaria mosquitoes
Rickard Ignell, PhD, Division of Chemical Ecology, Dpt of Plant Protection Biology, Swedish University of Agricultural Sciences (SLU)
ABSTRACT
Globally, malaria annually affects about 300 million people and causes about one million deaths, mostlyamong children in sub-Saharan Africa. In this region, the mosquito, Anopheles gambiae, is considered themost efficient vector of malaria. Due to its socio-economical importance, several countries are implementingvector control activities in an attempt to curtail the malaria epidemic. Vector control interventions, combininginsecticide-treated bed nets (ITNs) and indoor residual spraying (IRS) have suppressed An. gambiaepopulations in some malaria-endemic areas in sub-Saharan Africa. However, in other areas, such as thewestern part of Kenya, while the impact of ITNs and IRS on An. gambiae has been dramatic, theseintervention methods have had very little impact on the populations of An. arabiensis. There is growingevidence that the void created by the low populations of An. gambiae is being filled by An. arabiensis sincecurrent malaria infections in these areas are caused by the latter rather than the former species. The potentialfor a similar pattern of malaria infection, with An. arabiensis as the principal malaria vector, in other parts ofAfrica where the two malaria vectors co-occur after intervention with ITNs and IRS is very high.
A call has recently been issued for worldwide, integrated efforts to prevent further deterioration of themalaria situation. One such effort focuses on the exploitation of the chemical ecology of Anophelesmosquitoes to reduce the interactions with humans. In a recently initiated study we at SLU are trying todevelop a low-input bait technology for trapping and repelling An. arabiensis.
Chemoecological management of malaria mosquitoes
Rickard Ignell, PhDDivision of Chemical EcologyDepartment of Plant Protection BiologySwedish University of Agricultural Sciences (SLU)
Production and Carbon Dynamics in Sustainable Agriculture and Forest Systems in Africa Policy, Economics and Incentives Stockholm September 2010
Malaria is an Anopheles mosquito-borne disease caused by four species of the parasitic protist genus Plasmodium
Anopheles gambiae Plasmodium falciparum attackinghuman red blood cells
Global malaria distribution and endemicity
UNICEF, WHO 2005
Global human toll of malaria – malaria cases
Between 350 million and 500 million episodes of clinical malaria occur each year
Worldmapper project
Global human toll of malaria - deaths
1-1.5 million people die each year, predominantly in sub-Saharan Africa
Worldmapper project
In sub-Saharan Africa, malaria is one of the major causes of death of children under the age five, accounting for nearly 1 death in 5
UNICEF, WHO 2005
Distribution of deaths among children under age five by cause, global and sub-Saharan Africa, 2000–2003
Global human toll of malaria - poverty
Worldmapper project
“Malaria is both a root cause and a consequence of poverty. Malaria is most intractable for the poorest countries and communities in the world that face a vicious cycle of poverty and ill health”. The Earth Institute
Global human toll of malaria – gross domestic product
Worldmapper project
Malaria can decrease GDP by 1.3% in countries with high disease rates
Tabachnick, W. J. J Exp Biol 2010;213:946-954
The vector-borne disease episystem illustrating interactions betweenselected environmental factors with effects on the vector--pathogen--host epidemiologic cycle
In Africa, malaria is predominantly a rural disease where agriculture forms the backbone of the economy
0 20 40 60 80 100
0 1 2 3 4
Flooding rice irrigation
Non-flooding rice irrigation
Wet savannah
Sugarcane
Dry savannah
Various agro-ecosystems and crop production systems have an impact on mosquito productivity, and malaria transmission intensity.
% of mosquitoes
Plasmodium sporozite rate (%)
Mboera et al (2010) Geospatial Health 4(2), 2010, pp. 167-178
Mvomero district, Tanzania
Changes in agro-ecosystems and crop production systems may affect malaria transmission.
Kebede et al (2005) Am J Trop Med Hyg 73(4): 676–680
Bure
Malaria incidence rate/10.000 person-years
Mai
zecu
ltiva
tion
inte
nsity0 100 200 300
High
Medium
Low
Indoor residual spraying (IRS)
Insecticide treated mosquito nets (ITNs)
Vector control of malaria is the primary public health intervention for reducing malaria transmission at the community level
Other methods
Griffin et al (2010) Plos Medicine 7:e1000324
Interventions have resulted in major reductions in malaria transmission, and provided an efficient control of endophilic Anopheles mosquitoes
0 10 20 30 40 50
Permethrin
Deltamethrin
Lambda-cyhalothrin
Bendiocarb
DDT
Malathion
Insecticide resistance (%)
Cuamba et al (2010) Plos ONE 5: e11010
High levels of insecticide resistance in Anopheles mosquitoes has beenobserved in several regions of Africa
Chokwe District, Mozambique
Focuses on “…exploitation of the behavior and general ecology of the mosquitoes to reduce contact with human hosts…”
What it all comes down to:
C = Vectorial capacity, the number of infective bites received daily by a single host; m = Density of vectors in relation to density of hosts; a = Proportion of vectors feeding on a host divided by the length of gonotrophic cycle in days; V = Vector competence; P = Daily survival of vectors; n = Extrinsic incubation period
ma2VPn-logeP
C =
WHO’s call for worldwide integrated efforts to prevent further deterioration of the malaria situation
Chemoecological management of malaria mosquitoes
Curtesy of Prof. Laurence Zwiebel
Chemical cues play a significant role for mosquito behavior
Oviposition attractants Larval attractants
Host attractants
Main aim: identification of novel attractants that may be used in integrated vector management of Anopheles mosquitoes
Multi-pronged, comparative, approach
Odor collection
Physiological analysis
Molecular analysis
Behavioral analysis
What we have achieved so far
• Improved efficacy of existing ’general’ mosquito lure
• Novel identicatication of attractants for Culex quinquefasciatus, the major vectorof human filiariasis in Africa
• Identification of the first oviposition attractant of Anopheles mosquitoes
What we have achieved so far
SLURichard HopkinsTeun DekkerSharon HillBonaventure AmanMarcelo LorenzoMajid GhaniniaSiju PurayilShahid Majeed
Acknowledgement:
Carl Tryggers Stiftelse för Vetenskaplig Forskning