For decades, scientists have been trying to eradicate the disease, but many of their efforts have led to new health problems for people, or have placed unnecessary pressure on the ecosystems where chemicals have been implemented. The solution with arguably the most marked detrimental effect was DDT, a pesticide that resulted in birth defects among populations where it was sprayed. DDT was widely banned in the 1970’s, but scientists have continued the search for a way to end malaria – and the mosquitoes that spread it.
Most recently, researchers have been focusing on genetic modification. Last year, a British company called Oxitec announced method of genetically modifying male mosquitoes so that when they breed with females, the offspring cannot survive. Only the female spreads disease through her proboscis.
The company has set up test sites and pilot programs in places like Brazil, Panama and the Cayman Islands. The company claims an 80% reduction in the mosquito population in test areas. However, it is not known if the success rate is long-lasting or what the long-term environmental impact might be. Mosquitoes are a food source for birds, fish, bats and other animals, and there are some species that pollinate plants. There is limited research on how reducing mosquitoes might affect the ecosystems, but many ethicists argue that any such sweeping, man-made change is ethically questionable at best.
The University of Maryland has also conducted research where genetic modification is used to impact mosquito populations, but they focused on using the environment that the insects live in against them. The researchers modified a fungus to be deadly to mosquitos, and their tests found that mosquito populations died off entirely within 45 days.
To give the fungus a boost, the team engineered it to produce a toxin derived from the venom of the Australian Blue Mountains funnel-web spider. The researchers then tested it in a “MosquitoSphere”, a screen-enclosed setting in Burkina Faso, which was designed to mimic a village. Not only did this lead to the obliteration of the mosquitos, it proved as effective at killing insecticide-resistant mosquitoes as non-resistant ones.
While the fungus may have been effective, some worry that releasing a genetically engineered organism into the wild could cause unforeseen problems. Genetic engineering of fungus could have problematic negative public health impacts and unpredictable ripple effects on ecosystems, affecting pollinators, bats, and bees. In addition, a 45 day lifespan is long enough for the insects to pick up and transmit malaria.
Other promising research has found that sugar can potentially fight the disease. Focusing on the Asian tiger mosquito, researchers found that feeding young tiger mosquitoes sugar solutions caused a physiological response similar to that after feeding on blood. It also delayed their search for human blood.
Interestingly, the researchers found that sugar caused levels of a protein called vitellogenin to rise in the mosquitoes. Vitellogenin is an important component in the production of the egg yolk that provides nutrients to unborn mosquito offspring. Normally, vitellogenin is produced when receptors detect specific nutrients that mosquitoes gather from blood meals. Using gene interference experiments, the researchers were able to identify a specific gene associated with vitellogenin that, when knocked out, restored the mosquitoes’ attraction to humans.
Leaving sugar out for mosquitoes may put off younger mosquitoes from biting you, but it will make older mosquitoes stronger, and could weaken the defences of other mosquito species. We may, however, be able to genetically modify or treat tiger mosquitoes with hormones that raise vitellogenin levels in the absence of sugar, eliminating this trade off. Given that in most cases mosquitoes pick up disease pathogens during their first meal, such control methods could substantially delay the first blood meal of mosquitos, making them infectious for a shorter period of time.
While the efforts to eradicate malaria are laudable, the side effects of these kinds of solutions could be extremely far reaching. DDT should serve as a warning that we may not know for years after a solution is implemented what the effects on humans and our environment will be, and that it could be far worse than malaria.