Difficult to accept but useful for revealing the history of human infections and thus avoiding the problems associated with direct experimentation.
Mosquitoes have their uses. Especially female mosquitoes. ln particular, the buccal apparatus, which allows them to sting other animals and withdraw their vital fluids rich in proteins, is present exclusively in females because these fluids are necessary for the completion of the maturation of the eggs. While the males are “simple” pollinators and not bloodsuckers.
Put like this, the usefulness of their nutrient preferences doesn’t seem self-evident to us, just annoying. It is also true, however, that the blood they feed on can be full of useful information . In fact, a recent and innovative approach, presented at a conference on infectious diseases in Malaysia, manages to analyze in detail the last blood meals of mosquitoes with the aim of revealing evidence of infection in the blood of people or animals from which the insects they are fed.
The scientists who perfected this approach captured around 55,000 mosquitoes in parks in Brisbane (Australia) in 2021 and 2022. From these insects they extracted 2 milliliters of blood and analyzed it to check for antibodies capable of binding the virus Ross River, an alphavirus that triggers a debilitating mosquito-borne infection endemic to Australia and islands in the South Pacific Ocean. The virus belongs to a family that includes dengue, Japanese encephalitis, and yellow fever . The results showed that more than half of the blood detected was human, about 9% from cattle and 6% from kangaroos. Of the 253 samples taken from people, more than half had antibodies against Ross River virus. Nearly three-quarters of the samples from cattle and kangaroos also had evidence of past exposure.
In theory, the approach could be used “for virtually any pathogen that elicits an immune response in its host,” says Carl Lowenberger, an entomologist and parasitologist at Simon Fraser University in Vancouver, Canada.
The technique is exciting and could help researchers study some little-known diseases, “But it also comes with some serious limitations. For example, the data lacks details on where exposed animals and people were and when they were infected. This limits the use of the method to reduce the risk of virus transmission,” says Griffith University ecologist Eloise Skinner, although other scientists point out that the method could be used to study past infections in specific neighborhoods because mosquitoes tend to not to travel far.
The method could be used to study the past exposure of people and animals to a range of pathogens, avoiding the ethical and practical problems associated with direct experimentation.
“This is a fascinating new approach that demonstrates how we can innovatively use the environment around us to learn more about exposure to infections,” says Shelly Bolotin, vaccine scientist at the University of Toronto in Canada. It could also help detect diseases like Ebola and SARS-CoV-2 early in animals, says Niels Verhulst, who studies insect-borne pathogens, at the University of Zurich, Switzerland. And it could help scientists identify the animal host of a new virus, adds Verhulst, who tested the approach.
- Mosquito blood meals reveal history of human infections. (nature.com)