Some mosquitoes prefer to bite cattle than humans because of a genetic anomaly, thereby reducing the odds of them transmitting the malaria parasite. An effective way to fight the disease may thus be to genetically modify mosquitoes so that they adopt the same preference.
Around the world, 3.2 billion people are at risk of contracting malaria. The parasite causing the disease is carried by Anopheles mosquitoes that transmit it to humans by biting them. One of these mosquitoes is Anopheles arabiensis, the primary vector of malaria in East African countries.
Malaria transmission is driven by the propensity of mosquitoes to bite humans. When mosquitoes bite cattle, malaria does not spread because these animals are dead-end hosts. As for malaria control, it depends in large part on whether mosquitoes rest after their meals in places where they are likely to encounter insecticides.
In this study, published in PLOS Genetics, the scientists looked at the Anopheles arabiensis species, investigating whether its preference for humans or animals did have an impact on the rates of malaria transmission. The researchers wanted to find out whether there was a genetic explanation to the mosquitoes feeding on humans rather than cattle and to their resting behaviour and how these factors could protect humans against malaria.
Genetically modified to prefer cattle
Led by Bradley Main, from the University of California, Davis, the team sequenced the genomes of 23 human-fed and 25 cattle-fed mosquitoes collected both indoors and outdoors from the Kilombero Valley in Tanzania. An analysis of these genomes allowed them to identify a chromosomal rearrangement associated with cattle feeding. This rearrangement is known as the 3Ra inversion. It however did not appear to have an impact on the mosquitoes' resting behaviours.
The implications of these findings could be important. They could lead to scientists genetically modifying mosquitoes so that they end up preferring cattle over humans — thus stopping or reducing the spread of malaria. The idea is that using genetics can help scientists better understand and track mosquito behaviour to improve local control strategies.
"Whether there is a genetic basis to feeding preferences in mosquitoes has long been debated. Using a population genomics approach we have established an association between cattle feeding and a specific chromosomal rearrangement in the major east African malaria vector. This work paves the way for identifying specific genes that affect this critically important trait," Main concludes.