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Male leaf cutter bee peering over a rock purslane blossom
Villagers and cattle along the road near Pimperena in southern Mali. A UC Davis study reports that mosquito preference for human versus animal biting has a genetic basis. (Yoosook Lee/UC Davis)

Findings May Help Prevent Spread of Malaria

By Pat Bailey on November 10, 2016

We’ve all slapped enough marauding mosquitoes to be convinced that these tiny but irritating creatures don’t have discriminating tastes. They seem to feed on the first warm-blooded animal that happens to be in their line of flight.

But that’s not always the case, according to researcher Bradley Main of the Vector Genetics Lab at the UC Davis School of Veterinary Medicine. He and his research colleagues recently found that some mosquitoes are genetically wired to select cattle rather than humans for their next meal.

That’s good news because mosquitoes with this specific chromosomal rearrangement in their genome are less likely to transmit the disease-causing malaria parasite.

Main and team discovered this while studying the Anopheles arabiensis mosquito. This species is the primary transmitter of malaria in East Africa due to its broad host range and the fact that other mosquito species living closely with humans are killed by pesticide-treated bed nets, which are frequently used there.

This study, funded by the National Institutes of Health, is the first to use genomic tools to find a genetic basis for earlier observations that chromosomal rearrangements can be linked to a preference for cattle in mosquitoes.

The findings may help develop new methods for controlling mosquitoes and stopping the spread of malaria.

Genomic treasure hunt

The researchers, who published their findings in September in the journal PLOS Genetics, had set out to determine if a genetic basis exists to the resting behavior of the An. arabiensis mosquitoes and the human or animal hosts that they feed on.

Malaria transmission rates depend on whether mosquitoes bite humans or animals, and whether they rest after that meal in an area where they will encounter pesticides.

The scientists sequenced the genomes of 23 human-fed and 25 cattle-fed mosquitoes, collected indoors and outdoors from Tanzania’s Kilobero Valley. The sequencing allowed them to identify a genetic component that contributes to the mosquito’s host choice but not its choice of resting place.

They then narrowed their search and specifically identified the gene region associated with the cattle feeding trait as a chromosomal rearrangement called the “3Ra inversion.”

While the findings provide strong support that the chromosomal inversion in An. arabiensis is linked to cattle feeding, the researchers stress that a larger geographic area will need to be tested to confirm the connection. The work does pave the way for identifying specific genes that affect this critically important trait.

 

Pat Bailey of UC Davis News and Media Relations writes and supports communications about agriculture, animal health, food science and nutrition, and biotechnology.

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