New study suggests mosquitoes loaded with bacteria could stop the spread of dengue fever

Dengue has stopped spreading in the Australian city of Townsville after an army of mosquitoes infected with the virus. Wolbachia the bacteria were released. Indeed, when a natural bacterium called Wolbachia infects mosquitoes that carry dengue fever Aedes aegyptiit stops viral replication inside the mosquito and breaks the transmission cycle.

Mosquito Aedes aegypti on human skin. Image Credit: khlungcenter / Shutterstock

The million dollar question is whether these viruses or mosquitoes will eventually become resistant to the virus. Wolbachia or not? If the resistance emerges, the whole Wolbachia the exercise becomes useless.

A new study aims to provide a preliminary answer to this question. Researchers used a strain of dengue virus to infect two clbades of mosquito cells – one infected with Wolbachia and the other uninfected. the Wolbachia The bacterium naturally infects half of all species of insects, but is not found naturally in many species of mosquito vectors. The study titled "Supported Wolbachiablocked by intermediates of dengue virus isolates after serial pbadage in Aedes aegypti cell culture, was published in the journal Evolution of the virus June 8, 2019.

After five days, the replicated viruses were introduced into fresh cells, starting the next cycle of infection. Nine cycles have been completed in this way. In the end, the number of viruses was counted in each of two types of cell cultures. They also tested the replication capacity of the viruses of each culture using fresh cells of each type.

Normally, the dengue virus, like most viruses, diverts the machinery of the mosquito cell to reproduce, producing millions of viral particles. Finally, it destroys the host cell or its buds to release new viruses.

Wolbachia-the infected mosquito cells showed an exponential drop in the number of dengue viruses. In some cases, the virus is completely extinguished. however, WolbachiaNon-free cells showed a high and stable number of viruses.

Viruses collected from Wolbachiainfected cells were unable to replicate successfully even in Wolbachiafree cells. So Wolbachia rather acts as a vaccine, stopping viral multiplication inside the mosquito host. This is what is called "the pathogen blocking effect". The locking mechanism remains unclear.

Researcher Beth McGraw explains, "We think this could be due to competition between Wolbachia and the virus for the physical space (inside the cell) or for the nutrition they both need the mosquito. Or maybe Wolbachia increases the immune capacity of the mosquito. "

The dengue virus is responsible for millions of cases of dengue fever in the tropics. From fever, body aches and nausea, it can lead to life-threatening complications such as dengue haemorrhagic fever, generalized internal bleeding and organ failure.

Many traditional methods of dengue control have failed for a variety of reasons. For one thing, Aedes aegypti feeds during the day, so using bed screens at night does not prevent dengue fever. It breeds in stagnant waters, abundantly present in urban areas, which pose multiple problems of insecticide spraying and stagnant water disposal.

This is why viral biocontrol using Wolbachia is very attractive. First, it can control several types of dangerous viruses transmitted by mosquitoes. Secondly, uninfected female mosquitoes can not breed with infected male mosquitoes, which reduces reproduction rates. Instead of, Wolbachia is transmitted by infected female mosquitoes to their offspring, producing more and more infected mosquitoes in each generation.

Third, as the current study shows, neither the mosquito nor the virus could develop resistance to the bacteria after nine replication cycles.

"I am continually surprised by WolbachiaMcGraw said, "I thought we would have dengue variants that could create resistance. Wolbachia does a better job than expected to control the replication of the virus in the cells. "

Although the study is extremely promising for the prevention of mosquito-borne diseases such as dengue fever, much remains to be done. On the one hand, it was an in vitro study, using mosquito cells rather than the whole insect, which can react in a very different way. Second, the huge populations of mosquitoes in the real world offer much greater potential for acquired resistance than the limited populations of laboratory cells.

Scientists release now Wolbachia increased numbers of mosquitoes in tropical and subtropical countries to test its effects on human dengue levels. This could allow resistance, especially when the virus finds host hosts or uninfected mosquitoes.

"I think our study suggests that the evolution of resistance to Wolbachia in the virus is difficult, "McGraw said. I do not think it's a guarantee that the virus will not evolve on the ground, because the natural system is much more complex. The real experience is going on in the field right now, because Wolbachia has been released to communities in Australia, Indonesia and Brazil, among others. Surveillance in the release areas will be required to test the emergence of resistance to the virus. "