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Know your Enemy

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For the first time a genetic component to mosquito host choice behaviour has been identified in the major malaria vector An. arabiensis, using whole genome sequencing and a novel chromosomal inversion genotyping assay.

An. arabiensis has become the dominant malaria vector in many parts of East Africa; a collaboration led by the Department of Pathology, Microbiology and Immunology at UC Davis, USA, carried out an investigation, published in PLOS Genetics last month, which sequenced 48 An. arabiensis genomes of either cattle-fed or human-fed individuals from both indoor and outdoor resting sites in 3 villages in Tanzania, in order to look for SNP variation. 

Mosquito species that feed on human blood pose an enormous public health threat by acting as vectors transmitting numerous pathogens such as dengue virus, zika virus and malaria, which together kill more than one million people per year. The extent to which mosquito vectors feed and rest inside houses is a critical determinant of the effectiveness of current frontline control strategies including Long-lasting insecticide treated nets (LLINs) and Indoor Residua Spraying (IRS), which selectively kill mosquitoes that bite and rest indoors. It has also been shown that mosquitoes are less likely to rest indoors and bite humans when livestock are present. 

The identified genes were components of the An. arabiensis odorant detection mechanism; interestingly in the dengue and zika vector, Aedesaegypti, allelic variation in the odorant receptor gene Or4 has also been linked to human-biting preference

Given that human feeding is essential for malaria transmission, these results may help identify specific markers and tools for assessing the transmission potential of vector populations, and how their behaviour evolves in response to control measures. Dr. Bradley Main from the Vector Genetics Lab at UC Davis commented "This work paves the way for identifying specific genes that affect this critically important trait”.