Mosquitoes cannot spread COVID-19, Kansas State University finds after studying three most common vectors species
Mosquitoes are common vectors of a number of infectious pathogens, but WHO has maintained that COVID-19 is a respiratory disease that spreads through droplets and fomites.
One of the myths associated with COVID-19 was that the disease may spread through mosquitoes.
Mosquitoes are one of the most common vectors for a number of infectious pathogens, including the dengue virus, Zika virus, chikungunya virus and the malaria parasite Plasmodium. It would reasonable to worry about their possible association with a new disease.
However, the World Health Organisation (WHO) had stated quite early that COVID-19 is a respiratory disease that spreads through droplets and fomites and there was no proof of mosquitoes being able to spread the virus.
Mosquitoes and disease spread
Millions of people die every year due to mosquito-borne diseases in the world, as per the WHO. There are thousands of mosquito species in the world, however, only female mosquitoes of a few species spread diseases. These include Aedes, Culex and Anopheles.
The female mosquito needs blood to produce eggs. So they feed on human blood as well as the blood of various other animals, birds and reptiles. When a mosquito bites, they secrete saliva, which enters into your blood. This, in a way, acts like a fluid exchange. The mosquito gets infected with a pathogen (when it bites a sick person) and injects the pathogen into a healthy person when they bite someone after being infected.
SARS-CoV-2 and mosquitoes
A new study, done by researchers at Kansas State University and published in the journal Nature, suggests that the COVID-19 causing virus, SARS-CoV-2, cannot survive inside three of the most widespread mosquito species - Aedes aegypti, Aedes albopictus and Culex quinquefasciatus - even in extreme conditions.
As per the study, the original statement by WHO must have been based on the fact that none of the other coronavirus es like SARS or MERS virus produce enough viremia (virus in blood) for it to be able to be spread through mosquitoes. However, since previous studies have shown the spread of virus by mosquitoes even with low levels of the virus, it was important to find out if the new virus could survive in mosquitoes.
To be able to spread the virus, the pathogen should first go into the midgut (middle part of the alimentary canal) of the mosquito and from there it should spread to the other organs such as the salivary glands. For this, the virus would have to escape the various infection barriers present in the mosquito midgut.
So, to ascertain the presence and spread of the SARS-CoV-2 virus in mosquitoes, the researchers at Kansas State University inoculated a lot of mosquitoes from the three species mentioned above. Here are the findings:
- Out of the 15 mosquitoes tested within the first two hours of inoculation, 13 had the infectious virus. In the other two, the virus is believed to have lost its infectivity.
- Out of the 48 mosquitoes analysed, only one Aedes albopictus had the virus 24 hours after inoculation but the viral load remained the same, suggesting that the virus had not divided.
- No virus was found in the 277 samples tested after the 24 hour period.
Praising the efforts of the team, Dr Stephen Higgs, distinguished professor of diagnostic medicine and pathobiology at the University, said in a news release, “While the World Health Organization has definitively stated that mosquitoes cannot transmit the virus, our study is the first to provide conclusive data supporting the theory”.
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