Researchers at the Johns Hopkins Bloomberg School of Public Health announced that dengue virus infection in mosquitoes could make them hungrier and better at feeding.
A study published in the March 29 edition of PLoS Pathogens, found that the presence of the virus in the salivary glands of the mosquito activates certain genes that alter the mosquito’s sense of smell, immune system and even feeding behaviors.
"The virus may, therefore, facilitate the mosquito's host-seeking ability, and could — at least theoretically — increase transmission efficiency," lead author of the study, George Dimopoulus, said in a statement. "In other words, a hungrier mosquito with a better ability to sense food is more likely to spread dengue virus."
Dengue is spread to humans via the Aedes aegypti mosquito, which is found in tropical and sub-tropical climates around the world. The WHO estimates that roughly half of the earth’s population is currently at risk for dengue fever, particularly in Latin American and Asian countries.
In the past 40 years, the disease has seen a huge global increase in infection rates. Once only in nine countries worldwide, dengue fever is now endemic in over 100 countries and results in an estimated 50 to 100 million infections each year.
Nicknamed “breakbone fever,” the virus causes flu-like symptoms and joint pain in humans, and can be fatal in the event of severe complications. As there is no specific treatment or vaccine for dengue fever, much of the prevention and control lies with controlling the mosquito population that serves as its vector.
Because dengue is passed on to humans through the mosquito’s saliva, the presence of the virus in the insect’s salivary gland is vital for transmission. The study looked at gene response facilitated by the presence of the dengue virus in the mosquito’s salivary glands, and found that the virus affected the production of proteins associated with the insect’s sense of smell.
In addition to the odorant-binding proteins, researchers also found that infection affected a total of 147 genes, including those predicted to regulate feeding behaviors, immunity and virus transmission – though Dimpoulus said that the relationship between virus transmission and feeding efficiency is not yet fully understood.
Dimpoulus said it would be difficult to prove that infection with dengue virus truly makes the mosquitoes hungrier because scientists cannot infect humans with the virus.
In the laboratory model, the tests were conducted on a genome microarray, that is, pieces of Aedes DNA spread out along a glass slide. Live mosquitoes were then placed in an area where they had to drink dengue-infected blood from a balloonlike membrane. They were then given mice to feed on – far from the human blood meal they prefer.
“Mosquitoes will feed on other animals if they get hungry, but it isn’t their favorite dish,” Dr. Dimopoulos told the New York Times.
While previous studies have focused on the effect the virus has on cellular processes for the purpose of increased viral production, study researchers say these findings are the first of their kind.
"We have, for the first time shown, that a human pathogen can modulate feeding-related genes and behavior of its vector mosquito, and the impact of this on transmission of disease could be significant," Dimopoulos said in a statement.