Colorado State University Researchers Discover Why Mosquitoes Transmit Infectious Disease without Falling Ill, May Hold Key to Preventing Spread of Disease

Colorado State University researchers have discovered that mosquitoes that transmit deadly viruses such as dengue avoid becoming ill from the virus by mounting an immediate, potent immune response, but their immune system doesn’t completely eliminate the virus, allowing them to pass it on. The discovery is a step toward finding a way to prevent mosquitoes from spreading the virus to new victims.

Dengue fever and dengue hemorrhagic fever are major global public health burdens, with up to 100 million cases occurring annually, yet no vaccines or specific preventative medicines are currently available. The Aedes aegypti mosquito transmits dengue fever.  

"The mosquitoes that transmit dengue viruses have an immune response known as RNA interference," said Carol Blair, an expert in virus diseases transmitted by arthropods. "For years, researchers have wondered how mosquitoes can contract the virus but not become ill. Our research shows that a mosquito’s immune system does put up a defense against the virus, but that it doesn’t completely eliminate the virus. The virus multiplies within a mosquito’s salivary glands, allowing it to transmit the virus to the next host it feeds on.

"Finding a way to interrupt the growth of the dengue virus within the mosquito before it is transmitted would be a significant weapon. This new research suggests that the virus has evolved a way to get around the mosquitoes’ immune system. Finding out how the virus evades the mosquito’s immune response is an important next step in research that aims to fight disease by interrupting the growth of dengue virus within the mosquito before it can be transmitted," Blair said.

Various types of RNA exist in cells and arboviruses like dengue carry their genetic information in an RNA molecule. RNA interference is an evolutionarily ancient antiviral defense used by mosquitoes and other invertebrates to specifically destroy the RNA of many invading arthropod-borne viruses.

The Colorado State team of researchers recently proved that ramping up the RNA response in the mosquito did kill the dengue virus pathogen. In a paper to be published Feb. 13 in the public access journal PLoS Pathogens, they show that RNA interference – the immune response – is initiated within mosquitoes immediately after they take in blood containing dengue virus and that impairing the mosquito’s immune response increases the transmission of the virus.

The research was conducted in Colorado State’s Arthropod-borne and Infectious Diseases Lab in the College of Veterinary Medicine and Biomedical Sciences’ Department of Microbiology, Immunology and Pathology.