August 19, 2014 |

Immunize mosquitoes? A radical approach to stopping the spread of malaria

We call it a transmission-blocking vaccine (TBV) and it could break the never-ending cycle of malaria. How's it work?
Close up of a mosquito biting into skin against a green background.
Could a human vaccine to protect malaria-transmitting mosquitoes break the cycle of disease transmission? Photo: Penn State/James Gathany.

On August 20 the world marks World Mosquito Day—so called to commemorate the 1897 discovery by British doctor Sir Ronald Ross that malaria in people is transmitted to and from mosquitoes. Dr. Ross went on to win the Nobel Prize for his discovery, and since then, mosquitoes have been enemy number one when it comes to defeating a disease that takes a life every single minute—most of them young children in sub-Saharan Africa.

On this historic day, let’s focus on approaching malaria in a surprising new way: with a vaccine to protect those malaria-transmitting mosquitoes. That’s right—a vaccine to stop humans from giving malaria to mosquitoes.

If we can do this, we might finally stop malaria once and for all.

So, why protect mosquitoes from humans? First, you have to understand the vicious cycle of malaria, which works like this: a mosquito bites a girl and transmits the malaria parasite, perhaps causing her to get very sick. But it doesn’t stop there. A week later, a noninfected mosquito feeds on the same child, yet this time, it is the girl who passes the parasite to the mosquito. Soon, that mosquito—now carrying malaria parasites and buzzing around the same area, as mosquitoes typically do—bites the girl’s father, passing the parasite to him. Even if he shows no symptoms of malaria and doesn’t get sick, he can still pass parasites on to another mosquito that…well, you get the picture.

That’s where a vaccine comes in.

Zambian mother holding her infant.
Malaria is one of the most severe public health problems worldwide. It is a leading cause of death and disease in many developing countries, where young children and pregnant women are the most affected. Photo: PATH/David Jacobs.

A vaccine—we call it a transmission-blocking vaccine (TBV)—could break this never-ending and often deadly cycle. This type of vaccine actually prevents the mosquito that bites the malaria-infected person from getting infected, thus stopping the parasite’s life cycle in its tracks. If the mosquito doesn’t get infected, it can’t give malaria to another person.

Of course, vaccinating humans to protect mosquitoes from malaria might sound a little crazy. From polio to smallpox, we think of vaccines as preventing people from getting a disease. This type of vaccine wouldn’t protect someone bitten by an infected mosquito from getting malaria or lessen its symptoms.

But what it would do is help protect that person’s family and community. And if almost everyone in a community received such a vaccine, over time, the entire community would benefit by having fewer and fewer infected mosquitoes flying around and, therefore, fewer cases of malaria. Ultimately, this would create “community immunity” and eliminate malaria altogether from these areas. This long-term approach for the greater good—rather than immediate, personal protection—seems a bit novel, but the outcome would benefit us all: eradication of malaria.

Graphic of vaccines and the malaria lifecycle.
Three stages in the malaria lifecycle where vaccines could have an impact. Click to see larger graphic. Credit: PATH.

We’ve made remarkable progress, but innovation is still needed

While we’ve made extraordinary progress over the last decade in reducing malaria deaths, the wily malaria parasite is rapidly becoming resistant to some of our best tools—drugs and insecticide sprays. Another tool to break the cycle of transmission could help tip the balance against malaria, and history tells us that a disease is unlikely to be eradicated without a vaccine.

To reach the end game, we need a suite of new tools that would work together—a suite that includes a vaccine.

There are a number of potential transmission-blocking vaccines in early development. The program that I direct, PATH’s Malaria Vaccine Initiative (MVI), is working with partners to research a number of vaccine approaches. In collaboration with Fraunhofer USA, we have advanced their transmission-blocking vaccine candidate through early-stage clinical trials, and the National Institutes of Health is also testing at least one vaccine approach in early-stage trials. The Malaria Vaccine Technology Roadmap, updated by the international community in 2013, has called for vaccines by the year 2030 that reduce transmission to help eradicate malaria.

Should a transmission-blocking vaccine become a reality, it would be another critical tool that paves the way for eliminating and eradicating malaria.

So on World Mosquito Day, I’m calling for a vaccine to protect mosquitoes. Because ultimately, a world of malaria-free mosquitoes means a world of malaria-free people.

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