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London School of Hygiene & Tropical Medicine Malaria Centre

Malaria research in vector studies

Malaria Transmission Consortium (MTC) in the Western Kenyan Highlands.

LSHTM investigators:
Jonathan Cox, Chris Drakeley, Jennifer Stevenson, Mary Cooke
External collaborators:
Mary Hamel, John Gimnig, Kayla Laserson, John Vulule & Nabie Bayoh (KEMRI/CDC, Kenya); Neil Lobo, Brandy St. Laurent, Frank Collins (University of Notre Dame, USA); Ralph Harbech (Natural History Museum, UK).
Funding body:
The Bill & Melinda Gates Foundation through the Malaria Transmission Consortium.

MTC activities in western Kenya encompass a range of sub-projects that together address the need to develop standardized measures of malaria transmission as a means of assessing the effectiveness of programmatic interventions in unstable transmission settings.

This has included studies comparing a range of evaluation approaches (community and school cross-sectional surveys, community cohort studies, health facility monitoring and entomological monitoring).

As part of this work a Latin-square design experiment was carried out in 2010 to compare the suitability of different vector trapping methods in a highland fringe setting.  In the event a large proportion of the mosquitoes caught could not be identified definitively using available morphological keys or by using diagnostic PCR for Anopheles gambiae.  Subsequent genetic sequencing of ribosomal ITS2 and mitochondrial CO1 regions revealed that the majority of the mosquitoes, including those with malaria sporozoites, had unique unpublished sequences dissimilar to all known malaria vectors in the area (see figure ). Significantly, the most abundant clade of unidentified mosquitoes (42% of the specimens sampled) was  trapped outdoors and before 22:30 hours.  We are continuing to work with our collaborators at Notre Dame University to sequence mosquitoes caught by pyrethrum spray catch from across the district.

In late 2011 collaborators from the Natural History Museum collected and reared over 500 Anopheles larvae through to adult stages from the study sites. Sequencing of the ITS2 and CO1 region by Notre Dame collaborators will be linked to full morphological descriptions of the samples to fully describe any unusual species from the area.

A longitudinal survey is now ongoing to determine the relative importance of specific species (including newly-identified species) in terms of malaria transmission and to investigate species-specific host-seeking behaviours. Initial data support observations that  a substantial proportion of host seeking mosquitoes are sampled outdoors in the evening . This has potentially important implications in an area where vector control (in the form of IRS and LLINs) is predicated on the expectation of indoor, night time biting.