Malaria continues to be a major problem in the world today, killing more than 600,000 people annually (mainly children) and sickening more than 200 million.
We in the United States tend to think of malaria as a tropical disease that affects people living in developing countries. Yet it is important to remember that malaria used to be far more widespread. In fact malaria was once common throughout Europe, including as far north as Britain, and was widespread in the New World after being introduced in the 15th century. Today, Europe and North America are malaria-free (malaria was eliminated from the U.S. in 1952), and we tend to worry about the disease only when traveling to some destinations in Africa, Asia and South America. So why were we able to eliminate it from some parts of the world while it persists in others — at last count about 97 countries, according to the 2013 WHO World Malaria Report? The answer to this question is complex, but poverty is one of the major factors. Clearly the future control of malaria, or possibly its eradication, will depend on new strategies that work even in impoverished nations.
Approaches for malaria control were discussed at a recent Keystone Symposia conference on “The Science of Malaria Eradication” in Merida, Mexico. The conference was co-sponsored by the Malaria Eradication Scientific Alliance, in Barcelona, and brought together researchers studying different aspects of malaria control with the common goal of identifying strategies or combinations of strategies for a final assault on this ancient disease. Recent scientific advances in the field and many novel strategies for malaria control were discussed. The confluence of scientists with many distinct perspectives offered interesting insights into global efforts to control the disease.
The malaria parasite is transmitted via mosquitoes (referred to as “vectors”) and causes recurring fevers, which in severe cases can progress to coma or death. Strategies for malaria control focus on three primary concepts: (i) interfering with the parasite transmission cycle through vector control, (ii) providing immune protection through vaccination and (iii) administering anti-malarial drugs. The control of mosquito numbers (vector control) has traditionally involved spraying insecticides in mosquito breeding grounds, deploying toxic baits or using insecticide-impregnated bed nets. While these approaches can be very effective locally, there can be substantial costs in terms of potential effects on human health and the development of resistance in mosquito populations. Interesting alternative approaches include releasing sterile mosquitoes to reduce the ability of the insects to replicate. But the problem is that very large numbers of sterile insects have to be produced and released to have any measurable effect. Another strategy involves infecting mosquitoes with a certain species of bacteria, Wolbachia, that reduces their capacity to transmit malaria parasites. The challenge is to ensure that the bacterial infection is inherited by subsequent generations of mosquitoes so that the impact is sustained. A specific benefit of this latter approach is that it may have a long-lasting, or possibly permanent, effect. This approach may also be effective against other mosquito-transmitted diseases, such as dengue fever.
Developing vaccines against malaria continues to be a major focus of research. While there are some promising results (a recently tested vaccine had about 50 percent efficacy), a truly effective, durable vaccine easily deployed in the developing world does not seem imminent. Moreover, most vaccines under development do not target all species of the malaria parasite. However, a really interesting approach is the development of a novel form of vaccine that doesn’t protect the individual from disease, but prevents transmission back to the mosquito. The concept is that an infected individual would not serve as a reservoir for further transmission, thereby breaking the cycle of infection.
Finally, efforts continue to identify and develop new, cost-effective anti-malarial drugs to treat and control malaria. As always, there are concerns about side effects.
While vector control, vaccines and therapeutics are the mainstays of malaria control, all these approaches are critically dependent on strengthening the health systems in malaria-endemic countries. This not only includes delivering new drugs and vaccines in remote areas, but strong village-based surveillance programs and mass screen-and-treat operations. Fighting poverty as a critical aspect of malaria control was also discussed at the conference, and there was hope for considerable progress over the next decade. Indeed, many speakers at the conference echoed the words of Bill Gates (co-founder of the Bill and Melinda Gates Foundation) in a 2011 Reuters interview: “Eradicating malaria is not a vague, unrealistic aspiration but a tough, ambitious goal that can be reached within the next few decades.”
David L. “Woody” Woodland, Ph.D., is the chief scientific officer of Silverthorne-based Keystone Symposia on Molecular and Cellular Biology, a nonprofit dedicated to accelerating life science discovery by convening research conferences in Summit County and worldwide. Woody can be reached at (970) 262-1230, ext. 131, or firstname.lastname@example.org.
Today, Europe and North America are malaria-free, and we tend to worry about the disease only when traveling to some destinations in Africa, Asia and South America. So why were we able to eliminate it from some parts of the world while it persists in others?