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Parasite-Vector Interaction and Systematics

Source: TropIKA

Title of the session: Parasite-Vector Interaction and Systematics

Date: 6th November 2009

Agenda item: Scientific Session 38

Session theme: Vector interaction

Meeting room: Tsavo Ballroom 2

Chair(s): Martin Akogbeto/Cotonou Robert Sauerwein/Nijmegen

Presenters:

• Dr./John Gimnig/ US Centers for Disease Control and Prevention
• Dr./Jude Bigoga/ The Biotechnology Center, University of Yaounde I
• Dr Wamdaogo Guelbeogo/ Centre National de Recherche et de Formation sur le Paludisme 
• Dr./Timoléon Tchuinkam/ University of DschangChristophe Boete/ Institut de Recherche pour le Développement 
• Dr./Martin Donnelly/ Liverpool School of Tropical Medicine
• Papa Drame/ Institut de Recherche pour le Développement 

TropIKA rapporteur: Sabina Wachira and Daniel Kiboi

Major topics:

• Population replacement of an. Gambiae by an. Arabiensis mediated by the widespread use of insecticide-treated nets
• Estimation of infection rates and entomological inoculation rates (eir) in the African malaria vector: when should csp-elisa be the ultimate?
• Biting and resting behaviour of anopheles nili in north-western Burkina Faso
• Anopheles mosquitoes: not just flying malaria vectors... Especially in the field.
• Altitudinal and latitudinal variations in species composition of anopheles gambiae complex (Diptera: culicidae) along the volcanic line of Cameroon
• The vector population monitoring tool: DNA diagnostics for insecticide resistance monitoring in disease vectors
• Human antibody response to anopheles gambiae saliva: a new immuno-epidemiological marker to evaluate the efficacy of insecticides treated nets (ITNs)?

Keywords:

• Parasite
• Vector
• interaction
• biomarkers

Scope: The session covered the migratory patterns of the malaria vectors and the identification of the biomarkers for monitoring of infection and resistance detection

REPORT ON ORIGINAL SESSION

Overview

The behavioral, evolutionary and migratory pattern of the malaria vectors is a key feature in the control of malaria. Anopheles arabiensis has supplanted Anopheles gambiae in the western part of Kenya. The 7-year period shift is strongly attributed to the use of Insecticide Treated Nets and the feeding preferences of the species. Consistent with these results is that Anopheles arabiensis and Anopheles gambiae prefer human and bovine hosts respectively. Studies in North western Burkina Faso show unique adaptation of Anopheles nili. The vectors rest outside the houses and feed on humans indoor and outdoor. Although with low circumsporozoite protein, the species have importance in malaria transmission because of its anthropophagy. In biomarkers researches, Innovative Vector Control Consortium (IVCC), has developed a rapid kit for monitoring infection and insecticide resistance in malaria vectors, the kit comprises a multiplex of 11 assays into a single test

DNA ligation based SNP assays on an optical film biosensor chips, importantly, at US$ 1.50 and can genotype a single mosquito at all 11 loci. Finally, the interaction of the mosquito larva with micro-organisms can have immune consequences on the future potential interactions of the adult mosquito with malaria parasites.

CONTEXT AND ISSUE

Key facts and figures

The effect of insecticide treated nets on the survival and distribution of major malaria vectors Anopheles gambiae and An. Arabiensis

Need to develop infection and insecticides resistance monitoring tools targeting mosquito vectors

Need to understand the distribution and role of the Anopheles species in transmission of malaria parasite

Initiatives on the ground; experience/s derived

Classical salivary gland dissections, CSA ELISA confirmed by PCR and the Vectest, Mosquitoes collected by indoor spray catch and the CDC method for indoor and outdoor human dwelling, An. gambiae sampled by dipping, human landing and pyrethrum spray catches. DNA extracted and amplified in a PCR-rDNA and identified to sibling species. APCR-RLFP was performed to distinguish between molecular forms, whole genome microarray and mapping

Research Findings

Study done in north western Burkina Faso has revealed the increasing potential of An. nili rest as malaria parasite vector mainly due to its habitat preference, the vector rests outside the houses and feed on human indoor and outdoor.

The interactions of the mosquito larva with micro-organisms (soil microbe) have consequences on the future potential interactions of the adult mosquito with malaria parasites.

There is survival shift of previously dominant Anopheles gambiae to current dominance of An. arabiensis in western part of Kenya.

A study by IVCC (innovative vector control consortium) has developed rapid kits for monitoring infection and insecticides resistance in malaria vector. The kit is composed of a multiplex of 11 assays into a single test DNA ligation based SNP assay on optical thin film biosensor chip.

Seasonal variations of IgG antibody levels to An. gambiae saliva were observed (in Angola) before and after the installation of ITNs, and appeared to be associated with the exposure level to An. gambiae and the prevalence/intensity of malaria infection. Significant decrease of the anti-saliva IgG response was observed after ITN use which was correlated with the decrease of malaria parasitaemia, the current and referent criteria showing the efficacy of ITNs.

Lessons learned

• Use of insecticide treated nets reduce the Anopheles gambiae which prefers human host for blood meal but could potentially result to favor the dominance of Anopheles arabiensis which is difficult to control.

Issues raised, obstacles, difficulties

Future plans

• Metabolic resistance gene discovery in mosquitoes

FINDINGS AND CONCLUSIONS

IVCC (innovative vector control consortium) develops of rapid kits for monitoring infection and insecticides resistance in malaria vector. The kit is composed of a multiplex of 11 assays into a single test DNA litigation based SNP assay on optical thin film biosensor chip. At US $ 1.50, the kit can genotype a single mosquito at all 11 loci.

The resting and feeding patterns (rest outside the houses and feed on human indoor and outdoor) of An. nili in North western Burkina Faso shows that the species is a strategic malaria parasite vector.

The interactions of the mosquito larva with micro-organisms (soil microbe) have consequences on the future potential interactions of the adult mosquito with malaria parasites. Soil microbe induced immune response but the specificity of the immune cells induced is not known.

There is a survival shift of previously dominant Anopheles gambiae to current dominance of An. arabiensis in western part of Kenya. The shift occurred over a period of 7 years attributed to the use of ITNs and feeding preferences of the two species. Consistence with these results An. gambiae prefers human host while An. arabiensis prefer bovines. Although An. arabiensis is a less efficient malaria vector it is however difficult to control.

A novel biomarker, gSG6-peptide P1 for evaluating Anopheles mosquito bites identified. Seasonal variations of IgG antibody levels to An. gambiae saliva were observed (in Angola) before and after the installation of ITNs, and appeared to be associated with the exposure level to An. gambiae and the prevalence/intensity of malaria infection. Moreover, a significant decrease of the anti-saliva IgG response was observed after the ITNs use which was correlated with the decrease of malaria parasitaemia, the current and referent criteria showing the efficacy of ITNs.

From formal presentations

Public health Implications

Policy Impact

Use of IVCC rapid kits to assess the infection and insecticide resistance could provide critical information on viable intervention strategies to undertake.

Translational Research Impact

Knowledge gap created

• Exploring the specificity or non-specificity of the immune system induced by exposure of larva stage to microbes, how significant is it to development of malaria parasites in mosquitoes

• Investigating the metabolic resistance associated genes or network of genes in insecticides resistance in mosquitoes

• Investigation of allelic variation in insecticide resistance and insecticide metabolism in insecticide resistant mosquitoes

From open discussions/debates

• With regard to dominance of Anopheles arabiensis to Anopheles gambiae, the effects of the nets during high and low rainfall seasons was raised

• The issue of development of immune response against malaria parasite in mosquitoes on exposure of larva stage to microbes was questioned, how specific or nonspecific would the immune system be to the malaria parasite?

Identified conclusions

• Stringent measures will be required to control the dominating Anopheles arabiensis in western Kenya

• IVCC (innovative vector control consortium) rapid kit is crucial in monitoring of the infection and insecticides resistance

Main points of agreement

Identification of IVCC rapid kit screening 11 loci is positive towards elimination of malaria vectors

Main points of divergence

Targeting a single suspect gene could lead to wrong interpretation of resistance since resistance development involves network of genes

Recommendations

• Use of IVCC rapid kits to assess the infection and insecticide resistance

• Identifying stringent measures to control the dominating Anopheles arabiensis in western Kenya

• Further exploration of markers of resistance and other biomarkers targeting infection in mosquitoes

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