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Baiting Mosquitoes with Fake Blood

A Kentucky scientist has a plan to eradicate malaria.

by Daniel Oberhaus
Jul 17 2015, 9:00am

A female Anopheles albimanus mosquito feeding. Photo: CDC/Wikimedia Commons

By the time you hear the telltale droning in your ear, it's too late. Flail around all you'd like, but there is a proud member of the Culcidae family on a mission to ruin your day, and you can bet your ass it will not stop until it has sunk its proboscis deep into your fleshy extremities.

Once the itching begins, it will dawn on you that you've just become the latest victim of the vampire of the nematocerids, the terror of hot weather recreationists the world over. That's right—you've been bit by a mosquito.

If you're lucky, you will escape with your life, somehow managing to have avoided contracting malaria, Japanese encephalitis, dengue, yellow fever, chikungunya (which is exactly as unpleasant as its sounds), lymphatic filariasis, West Nile, tularemia, or Eastern equine encephalitis.

If not, you are probably now well on your way to becoming the latest casualty of a mosquito-driven onslaught that claims the lives of over 1 million people around the world each year.

More than 500,000 of those deaths are directly attributable to malaria, a parasitic infection spread primarily by way of infected female Anopheles mosquitoes. In mild cases, those infected with malaria can expect symptoms that range from fatigue and headaches to fever and vomiting. In the more extreme cases, the infected can experience jaundiced skin, seizures, coma, and death.

Malaria infections begin in the liver and eventually begin infecting blood cells. The parasite then reproduces in the blood stream, and, once it reaches a critical threshold, is then capable of being transmitted back to mosquitoes that bite the host.

"You can imagine that if we want to suppress populations of mosquitoes over large areas, we're going to need a lot of mosquitoes. Mosquito factories, if you will."

An estimated 198 million people were infected with malaria in 2013, according to the World Health Organization, making it a significant economic and health concern the world over. The problem is particularly acute in Africa, which accounts for 90 percent of the world's malaria deaths and sees a child die every minute from this preventable and treatable infection. Malaria was eliminated from the United States in the 1950s, but according to WHO over half the world's population is still at risk, with 97 countries reporting ongoing malaria transmission.

Fortunately the extent of the problem posed by malaria around the world is perhaps only matched by the magnitude of research being done to bring its death toll down to zero. Among the most promising new prophylactic techniques is being developed by Stephen Dobson, a professor of medical and veterinary entomology at the University of Kentucky, whose approach actually involves breeding more mosquitoes—and feeding them fake blood.

WWII era pamphlet aimed at mosquito population reduction; image via Wikimedia Commons

While it may seem counterintuitive to fight the spread of mosquito-borne illnesses by raising even more mosquitoes, the insects that Dobson is rearing are sterile. They're also male, which helps. "We can introduce lots of male mosquitoes because they do not bite or transmit disease," Dobson said.

Dobson's autocidal approach is part of a wide variety of sterile insect techniques that are currently being tested to eradicate mosquito populations, although many of his predecessors have had less than admirable success in this department.

"The general idea is you inundate a population with males that are effectively sterile," explained Dobson. "Traditionally [the sterilization] has been done with radiation: you irradiate the mosquitoes, screw up their DNA, and when they mate, the offspring don't hatch. This approach has worked really well with agricultural pests, but nobody has gotten it to work well with mosquitoes yet."

The problem with radiation is that what the mosquitoes gain in sterility, they lose in terms of fitness. Thus when scientists release their irradiated mosquitoes into wild populations they "fly three feet and then roll over and die," never able to come close to enticing wild females to mate with them.

Dobson and his team have rectified this approach by pursuing a different method for sterilizing their mosquito colonies, using a naturally occurring bacterium called Wolbachia instead of radiation. This allows their infected males to retain their fitness and efficiently breed in the wild.

According to Dobson, Wolbachia has already been demonstrated to be successful in controlling populations of Asian tiger mosquitoes and yellow fever mosquitoes in the lab, but is not quite ready for mass deployment to the areas that need it most. Now that he has demonstrated the potential in Wolbachia for sterilizing mosquitoes, the problem is figuring out ways to breed and infect enough mosquitoes to make it effective in the wild.

"You can imagine that if we want to suppress populations of mosquitoes over large areas, we're going to need a lot of mosquitoes. Mosquito factories, if you will," said Dobson. "To produce those mosquitoes, we're going to need a lot of blood meal because the females will need that protein to lay eggs. Currently, people use animal or human blood, depending on the mosquito species."

Dobson and his team, located in Kentucky, use blood supplied to them by local organic slaughterhouses. According to Dobson however, this is a luxury that is not available to everyone and is one of the primary impediments to the widespread use of his Wolbachia solution and other sterile insect techniques for mosquitoes.

"In places like the South Pacific and some of those islands. It's not trivial to find a slaughterhouse," he said. "It's difficult to find a regular source of blood and this is a real complication."

His continuing research, funded by the Bill and Melinda Gates foundation, will investigate ways to synthesize "fake" blood to rectify this problem, while continuing to conduct research using the Wolbachia bacterium to target mosquitoes carrying a species of parasite called plasmodium falciparum, which poses the greatest threat to humans.

Although he said he has seen encouraging initial results in his investigations into synthesizing an adequate blood substitute for use in breeding mosquito populations, there are a number of obstacles to be overcome and Dobson estimates that it will be at least two years before his fake blood is ready for deployment.

We are still far from declaring humanity malaria-free

"One [obstacle] is that we don't want this to be co-chain dependent. The resulting product should be able to be dried down or held at room temperature so that we don't have the logistical problems of delivering it," Dobson said. "A lot of these places don't have electricity, much less refrigerators, so that's not an option. We also want it to be relatively cheap and we want it to be as good if not better than blood for the mosquitoes to produce eggs."

Despite the challenges, Dobson believes the effort is worth it, if for no other reason than being able to produce large populations of Wolbachia-sterilized mosquitoes would represent a marked step forward in controlling dangerous mosquito populations.

"We are not eliminating mosquitoes period, we are targeting specific species and that's one of the attractive features of this approach," he said. "This isn't like flooding an area with a general chemical that's going to kill a lot of mosquitoes and butterflies—it's going to affect just that one species. We are doing small pilot tests with EPA approval and if we observe negative environmental effects, we can stop."

Solutions such as Dobson's, which focus on prevention by altering environmental conditions rather than treating those already infected, seem to be the trend in the fight against malaria. That being said, Dobson cautions against relying too heavily on any one particular approach.

"There is no magic bullet," he told Motherboard. "Integration of multiple methods is often the best response. The bottom line is that we need a robust tool box that allows for an appropriate and effective response, given disparate sets of conditions and scenarios."

Maternal malarial placenta. Image via Wikimedia Commons

There are historical precedents for the national elimination of malaria, most of which suggest that altering the environmental conditions is the most efficient way to halt the spread of the infection.

Take the United States for example, which in 1947 launched the National Malaria Eradication Program (NMEP) and succeeded in this goal by 1951. NMEP was conceived by the newfound CDC, whose first director also happened to be Georgia's foremost malariologist, an evolution of the Office of Malaria Control in War Areas which was created in 1942 to help control the spread of malaria around allied bases in the Second World War.

The eradication of malaria in the US was accomplished by spraying 6.5-million homes with the pesticide DDT, in addition to massive sustained efforts by the CDC to drain wetland sites and reduce mosquito breeding grounds. While cases of malaria still crop up in the United States today, nearly all of these cases are found in persons who had recently traveled abroad to countries where the transmission of malaria is still prevalent. The CDC completed its task within four years with only 369 personnel and a $1 million annual budget.

Nonetheless, this is still considered a hefty price tag for many of the countries where malaria poses the largest threat. We are still far from declaring humanity malaria-free.

That means that developing new efficient and cost-effective forms of treatment, in addition to mosquito eradication methods like Dobson's, continue to be important in combating malaria deaths around the world.

Dobson's approach could have ramifications for mosquito-borne illnesses beyond malaria, however.

"When I started my job here at Kentucky about 20 years ago, at that point nobody had heard of West Nile disease. West Nile is now everywhere in the US," he said. "We are unintentionally moving pathogens and mosquitoes around. For example, just in the last three years has three new invasive vector species have been established in California [and] now there is a new pathogen [chikungunya] circulating for the first time in the western hemisphere. This is all an effect of globalization and we should be concerned about mosquito borne pathogens."

Modern Medicine is a series on Motherboard about how health care and medical technology can move forward so rapidly while still being stuck in the past. Follow along here.