Scientifically Speaking | Mosquitoes as flying vaccinators against malaria?
Mosquito mouthparts act like a tiny syringe needle, so there’s a follow-up question that might pop into your head – why can’t mosquitoes act as flying vaccinators to prevent various communicable diseases? I explain
Mosquitoes are an annoyance. They also serve as inspiration for the design of needles that allow the drawing of blood relatively painlessly without damage of tissues in the skin. In fact, this is one of the reasons mosquitoes can stealthily bite us without getting noticed. Mosquito mouthparts act like a tiny syringe needle, so there’s a follow-up question that might pop into your head – why can’t mosquitoes act as flying vaccinators to prevent various communicable diseases? We could just go about our normal lives while getting surreptitiously bitten, and instead of worrying about contracting a disease, we might have a shot at preventing one.
My friend, the writer and social media icon, Sidin Vadukut asked this question on Twitter last year and got a whole bunch of snarky responses. (Seriously, I’m not sure what else anyone might expect from Twitter). But it was a valid question, and one that I stumbled on myself in thinking through plot details of a medical thriller that I never actually ended up ever writing.
Dear reader, now there’s evidence that mosquitoes as flying syringes can actually vaccinate for a serious mosquito-borne disease like malaria. Truth is stranger than (unwritten) fiction.
There’s a bit of history to this idea. In 2010, a group of Japanese scientists genetically engineered mosquitoes that made a protein that could act as a vaccine to prevent leishmaniasis (perhaps in people, but certainly in mice). The team led by Shigeto Yoshida at Jichi Medical University published their work in the scientific journal, Insect Molecular Biology. The idea received a lot of press coverage at the time, including in prestigious media outlets like Technology Review and Science. But serious technical challenges to creating the mosquitoes made the approach unfeasible for actual use. Then, there was the bigger concern of letting mosquitoes loose that could bite people and inject them with a medical product such as a vaccine without their explicit informed consent.
But ultimately the biggest issue was prosaic. Mosquitoes are unpredictable. They bite some people a lot more than they bite others. It would be technically difficult to dose vaccines based on the whimsical feeding patterns of mosquitoes. Some people might never get the right amount of vaccine, while others might get way more than they would need for protection.
Now, it seems that a few of these challenges have been addressed for a malaria vaccine that is delivered via mosquito bites in a closed, laboratory setting. In this case, to create a malaria vaccine, researchers led by Lisa Jackson at Kaiser Permanente Washington Health Research Institute and Stefan Kappe at the University of Washington didn’t genetically engineer mosquitoes, they engineered malaria parasites that were defective and unable of causing disease. This type of weakened whole-parasite vaccine is commonly used for many other diseases and it seems to work for malaria too.
In the study published in Science Translational Medicine, mosquitoes were infected with malaria parasites lacking three critical genes. These three genes are needed for malaria to occur in humans.
Study volunteers received around 200 bites per sitting on their arms. The total vaccine was administered through 1,000 mosquito bites. If that sounds alarming then the researchers reassure that even though some people had reactions to mosquito bites, these were usually temporary.
The researchers then subjected volunteers to “controlled human malaria infection” about a month after their final series of mosquito-bite vaccinations. Basically, what happened is that mosquitoes which have normal malaria-causing parasites bit study volunteers. If a volunteer developed disease, antimalarials were provided to cure illness.
The researchers found that about half of those who were vaccinated by mosquito bites were protected completely against infection. This number may seem low, but the scientists were not discouraged that the experiment didn’t result in even greater efficacy.
Though their experiments show that vaccine delivery by mosquitoes does actually work, there are drawbacks that limit the practical use of this method. Much of the vaccine stays in the skin after a mosquito bite instead of going to other parts of the body where it might elicit a stronger immune response.
So ultimately, even if this malaria vaccine gets approval for broader use, it is unlikely to be actually delivered by hundreds or thousands of mosquito bites. Injections by syringes offer several benefits that can’t be dismissed just yet.
Anirban Mahapatra is a scientist by training and the author of a book on COVID-19. He’s writing a second popular-science book
The views expressed are personal