Written by Kabir Firaque, edited by Explained Desk |
Updated: July 20, 2020, 8:25:46 am
So far, there has been no evidence that mosquitoes can spread the novel coronavirus that causes Covid-19. Now, Kansas State University scientists have provided evidence that mosquitoes actually can’t. Their study is published in Nature Scientific Reports.
Wasn’t that already known?
There was no confirmation until this study. “So far there has been neither information nor evidence that the new coronavirus could be transmitted by mosquitoes,” says the World Health Organization (WHO) in its Mythbusters section on Covid-19, which was first published in March.
However, the WHO was certain that mosquitoes could not transmit the virus. The new study calls this a guess and says it may be based on “various observations and facts extrapolated from other coronaviruses”. For example, the coronaviruses that cause SARS and MERS produce relatively low levels of virus in the blood compared to the levels found when mosquitoes are infected with dengue and yellow fever.
So what has been proven now?
The researchers have shown in laboratory experiments that SARS-CoV-2 cannot infect mosquitoes. It is the first such confirmation. “We went out of our way to infect the mosquitoes even though the conditions we used did not occur naturally,” Stephen Higgs, director of the Biosecurity Research Institute at Kansas State University, told The Indian Express via email.
The mosquitoes were not infected even under these extreme conditions.
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What does it mean for a mosquito to get infected?
If replication is occurring, there should be enough virus in the blood to indicate this. “The more viruses there are in the blood, the more likely it is that the mosquito will become infected,” Higgs said. “But not all types of mosquitoes are susceptible to infection. We don’t know what makes some mosquitoes susceptible and others resistant. “
Take the examples of dengue fever and yellow fever. In SARS and MERS, coronavirus levels do not reach dengue virus or yellow fever virus levels, which are believed to be high enough to infect a mosquito.
Higgs cited the mosquitoes that spread dengue fever and chikungunya. These are transmitted by Aedes aegypti, which is susceptible, but not by Anopheles species, which are resistant. “You can see it differently and say that some viruses can infect some mosquitoes and others not, that the dengue virus infects Aedes, but not Culex. Again we don’t quite understand, ”said Higgs.
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So which mosquitoes are not infected with the new coronavirus?
The experiments were carried out on three common and widespread mosquito species. Aedes aegypti, Aedes albopictus and Culex quinquefasciatus. The first two types are the vectors for dengue fever, chikungunya, zika fever, and yellow fever. Culex quinquefasciatus spreads viruses that cause lymphatic filariasis and certain types of encephalitis.
All three types occur in India. The coronavirus could not replicate in any of them.
How were the experiments carried out?
In order to become infected, a mosquito must feed on blood with viruses. “Instead of feeding mosquitoes infected blood, we actually injected the virus into the mosquitoes,” Higgs said.
“The reason we did this was because it was an extreme test of mosquito susceptibility to viruses. If the virus doesn’t grow when injected, we can be sure that a mosquito that feeds on someone with a lot of virus in their blood will not get infected, ”he said.
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