Challenge 3: Block Transmission
The secret to ending malaria could be protecting mosquitoes from humans
As villains go, the mosquito is well cast. The tiny pest is unique in nature in two important respects. First, it has no redeeming value to the broader ecosystem (the name of the particular breed that transmits malaria, “Anopheles,” actually means “useless” in Greek); and second, the mosquito is by far the deadliest creature on the planet to human beings, claiming 725,000 lives a year—principally to malaria, but also to diseases including dengue fever and West Nile virus.
Even Disney, the company that made ants and lobsters lovable, has it in for the mosquito. In a now-famous 1943 animated short titled “the Winged Scourge,” a Disney narrator brands mosquitoes “public enemy number one” for transmitting malaria, and cheers as the Seven Dwarves gleefully pump insecticide and stomp the bug.
Our first two columns explored how finding the parasite(link) and completely curing(link) infected people are two of the keys to ending this disease. The missing piece is to block transmission and stop the endless shuttling of the parasite back and forth between man and mosquito.
You see, for malaria, the transit between mosquito and man isn’t just a joy ride—it’s an essential step in reproduction. By blocking transmission you isolate the mosquito and interrupt that process. In mosquitoes, the parasites die quickly due to their host’s short life spans; and the ones in humans stay contained until you can eliminate them with medication.
The classic approach to blocking transmission is to protect people from mosquito bites using bed nets or insecticide sprays. And make no mistake, these tools have been extraordinarily effective: a major factor in saving 3.3 million lives from the disease since 2000.
Rethinking the Problem
But to break the back of transmission, we have to rethink the problem. We must move beyond vilifying the mosquito—and the key may be protecting mosquitoes from humans.
Surprised? You shouldn’t be. Consider that mosquitoes only carry the malaria parasite for up to 30 days—a mosquito’s maximum lifespan—while humans can carry the parasite for decades if left untreated. And where mosquitoes can only travel a mile or two on their tiny wings, humans circle the globe transporting the parasite like carry-on luggage. So if we’re looking for someone to blame for malaria transmission, we must start by taking a hard look in the mirror.
The surest way to avoid getting malaria from mosquitoes is to stop giving it to them. That’s why a new generation of treatments that completely eliminate the malaria parasite from the human body will be so important (for more, read Challenge 2: Complete Cure). But it is only one of the novel approaches that will make it possible to stop transmission.
Next Generation Protection
Soon, the tried-and-true bed net may be joined by new vector-control technologies that use radar-jamming molecules to disguise humans from mosquitoes. That’s the goal of a technology called Kite Patch, which took the crowd-funding site Indiegogo by storm. Worn on your clothes, this small sticker is a spatial repellent that blocks a mosquito’s ability to register carbon dioxide. In effect, it acts like Harry Potter’s cloak of invisibility, making people virtually undetectable to mosquitoes. (Read more about the Kite Patch technology and what it could mean for malaria.)
This past summer, the pharmaceutical company GlaxoSmithKline registered for regulatory review of the first partially effective malaria vaccine—called RTS,S—and hopes for a WHO seal of approval as early as 2015. In clinical trials, the vaccine reduced the number of malaria episodes by a quarter in infants immunized and cut in half malaria cases in older children (toddlers) - low by vaccine standards, but unprecedented in terms of malaria.
But even as we celebrate this milestone – the first vaccine against a parasite – the focus of research is moving beyond only protecting individual people against malaria symptoms (as RTS,S does) to blocking transmission.
New vaccine approaches target two “choke points” when parasites are at their fewest in number during their complex life cycle: the transitions from mosquito to man, and from man to mosquito. These potential vaccines could effectively hold the line against onward transmission of the parasite, stopping malaria dead in its tracks.
Despite the PR campaign against mosquitoes, the goal of malaria control has never been to eradicate the insect, but only to control it as a way to get at our true adversary: the parasite. Little did we suspect that the key to eradicating malaria around the globe could involve making the mosquito an asset in the malaria fight.