Chemoecological Management of Malaria Mosquitoes

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