The eggs of Zika virus carrier mosquitoes can survive desiccation caused by changes in metabolism, which offers a potential control strategy. A new study shows that the eggs of Zika virus carriers can tolerate prolonged periods of desiccation due to changes in metabolism.
Institute for Stem Cell Science and Regenerative Medicine in Bengaluru, India and Indian Institute of Technology in Mandi, India Anjana Prasad, Sunil Laxman (Sunil Laxman) of Mandi, and colleagues published a new study in the open-access journal "PLOS Biology" on October 24, saying that Zika virus-carrying mosquito eggs can tolerate long periods of desiccation by changing their metabolism. The discovery offers potential new ways to control the spread of this mosquito.
Cells are mostly made of water, and desiccation can be fatal to any living thing because the structure of many proteins and other cellular molecules depends on adequate moisture. While many species of microorganisms have evolved mechanisms to survive desiccation, only a few animals have. One such mosquito is the Aedes aegypti mosquito, which is a carrier of several viral diseases, including Zika, dengue, yellow fever and chikungunya. Originally found in North Africa, the Aedes aegypti mosquito has spread globally, posing a threat to warm and humid areas around the world.
Aedes aegypti eggs take 48 to 72 hours to hatch into larvae, and the authors first demonstrated that eggs must be desicated for at least 15 hours to survive; eggs that were desiccated before this stage were unable to hatch after rehydration. They then compared the proteomes of surviving eggs with and without desiccation and found a number of significant changes in metabolic pathways within desiccated eggs. These changes include increased levels of enzymes in the tricarboxylic acid (Krebs) cycle that promote lipid metabolism, and decreased levels of glycolytic enzymes and ATP-generating enzymes in the TCA cycle, which together shift cellular metabolism toward the production and use of fatty acids. Overall, metabolic levels decreased, while levels of the amino acids arginine and glutamine increased. Additionally, enzymes that reduce the damaging effects of oxidative stress, a known consequence of dehydration, were also increased.
Arginine molecules join together to form polyamines, which are known to help protect nucleic acids, proteins, and membranes from various types of damage. Here, the authors found that eggs accumulate polyamines, suggesting that polyamines may be a key aspect of desiccation resistance. To test this, they fed egg-laying female mosquitoes a polyamine synthesis inhibitor. The eggs they lay are significantly less viable in dry conditions than eggs laid by untreated female mosquitoes. A second inhibitor, an inhibitor of fatty acid metabolism, also reduced egg survival after desiccation. Finally, they found that this fatty acid inhibitor reduced polyamine synthesis, suggesting that one role of increased fatty acid breakdown is to provide the energy needed to produce protective polyamines.
"Given the importance of Aedes aegypti, the major vector of multiple viral diseases that affect nearly half the world's population, and the rapid geographic expansion of this mosquito vector, these results provide a basis for reducing Aedes egg survival and global spread," said Laxman. "In addition, some of the specific inhibitors described here that reduce egg desiccation tolerance in Aedes aegypti, as well as new inhibitors that affect other steps in the egg desiccation tolerance pathway, may prove to be useful vector control agents."
Laxman added: "Aedes eggs can survive indefinitely and hatch into viable larvae after they are completely dried out. The embryos restart their metabolism after drying out, protect themselves by desiccation, and reawaken when water becomes available."