A team of researchers at The Pirbright Institute have used genetic engineering to disable the chikungunya virus genome in mosquito cells. With further development, the technology could help researchers to engineer disease resistant mosquitoes, which would make them unable to spread chikungunya between animals and people.
Chikungunya virus infects monkeys, birds, cattle and rodents in many tropical and subtropical regions, and can be transmitted to people by Aedes aegypti and Aedes albopictus mosquitoes. Human symptoms include fever, vomiting and joint pain that can last weeks or months, sometimes even years. The disease has no vaccine or treatments so new methods are needed to control outbreaks that place a major burden on healthcare systems.
In a study published in Nature’s Communications Biology, Pirbright researchers demonstrated that a gene editing tool called CRISPR/Cas13b could identify and disable a specific chikungunya virus gene in mosquito cells, which could prevent the growth of the virus. CRISPR/Cas13b has already been used in other studies to knock down viruses in plant and mammal cells, but this is the first time the system has successfully been utilised in insect cells.
The study was carried out with a laboratory model so confirmation the system works with live virus is needed, but the findings show CRISPR/Cas13b could be employed as a tool for genetically engineering disease resistant mosquitoes.
CRISPR gene editing has become a popular method for modifying organisms in the last decade as the system can be easily programmed to target very specific gene sequences for editing. It works by using a genetic sequence known as a ‘guide’ to direct a CRISPR associated (Cas) protein to cut a target gene. Each Cas protein has different properties, so it is important to select the correct one for the task at hand.
The team chose Cas13b as it is able to cut RNA, a genetic cousin of DNA, which makes up the chikungunya virus genome. Cas13b can also use strings of multiple guide sequences that contain instructions to cut several different genes, which can help against the possibility of resistance emerging in the virus.
Professor Luke Alphey, head of the Arthropod Genetics Group, said: “Now we have shown CRISPR/Cas13b can be used in mosquito cells, disabling multiple chikungunya virus genes is our next goal. Although we think our single gene knockout would be enough to stop the virus replicating in mosquitoes, the virus might be able to evolve around this, making the genetic engineering redundant. Additional knockouts would therefore make it far more challenging for chikungunya virus to adapt, ensuring the protection offered is robust.”
As well as a new tool for engineering chikungunya resistant mosquitoes, CRISPR/Cas13 could potentially be used against other major mosquito-borne viruses that have RNA genomes, such as dengue and Zika.
This research was funded by Wellcome and the Biotechnology and Biological Sciences Research Council (BBSRC), part of UK Research and Innovation (UKRI).
Image shows genetically engineered mosquito expressing different fluorescent markers to show it has successfully taken up three separate genes. The present study was carried out using cellular models, but could progress to live mosquitoes if further studies are successful.