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Mosquito blood meals reveal history of human infections

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The blood of the mosquito’s last meal contains antibodies from the last person or animal the mosquito ate.Credit: Claude Nuridsany & Marie Perennou/Science Photo Library

Blood-sucking mosquitoes have uses. An innovative approach to analyzing their last blood meal can reveal evidence of infection in humans and animals eaten by flying insects.

Scientists, presented at the Infectious Diseases Conference in Malaysia last week, could use this approach to study past exposures of humans and animals to various pathogens, allowing them to be tested directly. It avoids the ethical and practical issues of doing so.

“This is a novel and fascinating approach, and an innovative way to use the environment around us to learn more about our exposure to infection,” said Shelley Bolotin, a vaccine scientist at the University of Toronto, Canada. It shows,” he said.

It could also help with early detection of animal diseases such as Ebola and SARS-CoV-2, says Niels Verhulst, who studies insect-transmitted pathogens at the University of Zurich in Switzerland. It could also help scientists identify animal hosts for new viruses, adds Verhulst, who tested the approach.

man, cow, kangaroo

Previous studies have detected past exposure to pathogens by testing for antibodies, markers of past infection from specific animal hosts.1The technique used by Carla Vieira, a disease ecologist at the QIMR Berghofer Medical Research Institute in Brisbane, Australia, can detect antibodies in the blood of a wide variety of animals and humans.

Vieira focused on the Ross River virus, a potentially debilitating mosquito-borne disease endemic to Australia and South Pacific islands. This virus belongs to a family of viruses that includes dengue fever, Japanese encephalitis, and yellow fever.

Vieira and her colleagues have caught around 55,000 mosquitoes in Brisbane parks in 2021 and 2022. A few milliliters of blood were squeezed from recently eaten insects and tested for antibodies capable of binding to the Ross River virus. They also sequenced DNA fragments in the blood to identify animal hosts that the insects were feeding on.

In preliminary results presented at the International Conference on Communicable Diseases in Kuala Lumpur on November 20, Vieira reported that 480 of the trapped mosquitoes were filled with blood. More than half of them ate people, about 9% ate cows, and 6% ate kangaroos. Of 253 human samples, more than half had antibodies to Ross River virus. Nearly three of his quarters of cows and kangaroos also had evidence of being exposed in the past.

in another study2 Verhulst and his colleagues, published in January, detected antibodies to SARS-CoV-2 and the parasite toxoplasma gondii Mosquitoes feed on animals such as alpacas and cats.

Future tasks

In theory, this approach could be used “for almost any pathogen that provokes an immune response in the host,” says Carl Lowenberger, an entomologist and parasitologist at Simon Fraser University in Vancouver, Canada.

The technology is exciting and could help researchers study certain little-known diseases, such as Japanese encephalitis in Australia, says Eloise Skinner, a disease ecologist at Griffith University on the Gold Coast. said. “But it also comes with some severe restrictions.” For example, the data lack details about where exposed animals and people were and when they became infected. This limits its use for reducing the risk of viral infections, she says.

But because mosquitoes don’t tend to travel long distances, the approach could be used to study past infections in specific areas, says Bolotin.

Another drawback of the technique is that it’s not clear how well the proportion of blood samples containing antibodies reflects the proportion of people actually infected, says David, a medical epidemiologist at the University of Queensland in Brisbane. Harley said. Multiple mosquitoes may have eaten the same person.

Blood-sucking mosquitoes are also notoriously difficult to catch, Skinner says, which limits the use of the technology in outbreak surveillance. After being filled with blood, female mosquitoes typically find dark, damp places to hide and try to digest, he says.

Verhulst and his colleagues created a formulation based on the attraction of mosquitoes to carbon dioxide produced by fermenting molasses and captured more blood-filled mosquitoes than without the formulation. did.3They hope to test it outside the lab soon.

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