Immunity genes of virus-transmitting mosquito identified
Researchers have identified the genes behind the immune system of the mosquito Aedes aegypti, which is responsible for transmitting the viruses which cause dengue fever and yellow fever. Between them, these diseases infect over 50 million people worldwide every year. The scientists hope their new-found knowledge could be used to help the insects fight off these viruses more effectively, and so prevent transmission to humans. The work, which was partly funded by the EU, is published in the latest edition of the journal Science. Drawing on the recently sequenced genome of A. aegypti, the scientists identified over 350 genes which are involved in the mosquito's immune system. They discovered that these genes evolved much faster than the rest of the genome. The researchers also compared A. aegypti's immunity genes with those of the Anopheles mosquito and the harmless fruit fly, Drosophila melanogaster. They found that while the two mosquitoes had some genes in common, there were also many differences. The scientists believe the insects' immune systems evolved rapidly in response to the different pathogens they encountered. 'Our study has revealed the genetic 'landscape' made by parts of this mosquito's newly-sequenced genome which are involved with immunity,' said Dr George Christophides of Imperial College London, the senior author of the paper. 'By working to understand as much as possible about these genes, and the way they interact with specific pathogens, we hope to gain a more complete understanding of the mechanisms by which a pathogen either survives inside the insect body, or is killed by the insect's defences.' The next step for the researchers is to deepen their understanding of function of the newly-identified A. aegypti immunity genes. They will also investigate whether the genetic differences between the Anopheles and Aedes mosquitoes explain why the first transmits malaria while the latter transmits dengue and yellow fevers. The work comes at a time when the prevalence of both dengue and yellow fevers is on the rise. Yellow fever is found in many tropical regions of Africa and the Americas. Although an effective vaccine against the disease exists, many people in affected areas remain unvaccinated and according to the World Health Organisation, there are around 200,000 cases of the disease every year, and 30,000 deaths. Dengue fever is found in tropical and subtropical regions around the world, particularly in urban and semi-urban areas. There are an estimated 50 million cases a year. In some cases a complication called Dengue haemorrhagic fever (DHF) can develop. Although there is no treatment for dengue fever, with intensive care the mortality rate from DHF can be cut dramatically. Because Dengue fever is caused by four different viruses, developing a vaccine against the disease is difficult. EU funding for the project came through the BioMalPar Network of Excellence.