Another Study Confirms Mosquitoes, Midges Don’t Transmit Coronavirus
By Melissa Mayer
If you take anything from this post, Juergen Richt, Ph.D., DVM, hopes it’s this: Entomologists and veterinarians play a vital role in public health and biodefense. In fact, Richt considers his biosafety level 3 (BSL-3) facility and 20-person team an elite unit. And that crew is taking on COVID-19.
A new article published March 4 in the Journal of Medical Entomology describes how researchers from Kansas State University and the U.S. Department of Agriculture’s Agricultural Research Service evaluated whether mosquitoes and biting midges can serve as biological vectors for COVID-19. Their results align with numerous studies conducted thus far.
“The answer is none of these seem to support SARS-CoV-2 replication,” says Richt, Regents Distinguished Professor of Veterinary Medicine at Kansas State University and Director of KSU’s Center on Emerging and Zoonotic Infectious Diseases (CEZID). “So, we think that these species are unable to be biological vectors of SARS-CoV-2.”
Elite Facility, Elite Team
To find that answer, Richt and his team fed Culex tarsalis and Culex quinquefasciatus mosquitoes and Culicoides sonorensis blood spiked with SARS-CoV-2, the coronavirus that causes COVID-19. They also tested cell lines to see if the virus could replicate in culture.
The team works with SARS-CoV-2 and other deadly pathogens in a BSL-3 lab. An entomologist working in the lab’s insectary must wear a Tyvek suit and respirator and exit through a submarine door, which prevents insects from escaping the negative pressure inside the lab. In that dirty change room, they remove their safety gear and scrubs and step through another door to shower and don clean scrubs and a mask for the BSL-3 common area. To get to their street clothes, they go out through another dirty change room and shower again.
So far, the team has used this facility to look at a host of questions about COVID-19. And the findings in this case were good news. While they found some low-level viral RNA 10 days after the insects took their infected bloodmeal, they didn’t find any infectious virus in those insects or the cell lines. That means those species aren’t likely biological vectors for SARS-CoV-2.
That tracks with what we know about coronaviruses, which so far have never been arthropod-borne. SARS-CoV-2 is a respiratory virus that’s mainly passed on through droplets called aerosols. To be transmitted by mosquitoes, a virus must get through the insect’s gut, infect its salivary glands, and then hijack the mosquito’s cell machinery to replicate. If the virus can’t replicate, it’s a dead end for the virus. In the realm of viruses, a relatively small number have evolved to commandeer mosquitoes’ or other arthropods’ internal systems for transmission, and all research thus far indicates SARS-CoV-2 is not one of them.
The question becomes a bit less certain when you move from biological vectoring to mechanical vectoring, in which an insect picks up viral particles on surfaces (sometimes called fomites) and physically moves them on its body. To answer that question, Richt and his team are looking at house flies, and those results might be pertinent to mosquitoes and biting midges, too.
“Maybe mosquitoes and midges can be mechanical vectors. That’s something we could revisit,” says Richt. “There are some cases where we don’t understand how COVID was transmitted … and we believe that, in some of these cases, where you cannot find any direct transmission of the virus from interaction with positive people, that fomites in various ways could play a role. And in this scenario, you can add mechanical transmission by mosquitoes, flies, et cetera.”
Richt says the work done in his lab protects agricultural systems and public health as his team stands in the gap on important issues like food security and zoonotic diseases. It’s not just science; it’s biodefense—and Richt is ready for the public to see that research labs are just as vital to national security as an F-15.
“We had a lot of luck in 2003 with SARS … and we had very good luck in 2009 that H1N1 was not so virulent, but … the next one could be as bad as SARS-CoV-2, or even worse,” he says.
And when that happens, Richt and his team will be ready.
Journal of Medical Entomology
Melissa Mayer is a freelance science writer based in Portland, Oregon. Email: firstname.lastname@example.org.