James W. Kzura, M.D., President of the American Society of Tropical Medicine and Hygiene, explained: "Both of these studies demonstrate the incremental successes and long-term challenges faced by our drive to prevent needless deaths due to malaria. Make no mistake, this is a winnable battle. We can and will ultimately eradicate malaria from its strongholds in Africa and Asia."
In the first study, researchers at North Carolina Central University (NCCU) and Duke University examined data from 13 studies about the impact of indoor residual spraying (IRS) on malaria transmission in various settings, notably in Africa. IRS involves spraying insecticides inside homes or community buildings in order reduce the number of infections by killing malaria-carrying mosquitoes.
Dohyeong Kim, Ph.D., lead author of the study and a professor in NCCU's Department of Public Administration, said:
"Our findings show that during the last decade IRS has remained a powerful tool for fighting malaria, even though mosquitoes, particularly in Africa, are developing the ability to evade widely used insecticides."
Although IRS is known to significantly reduce malaria infections, what factors influence the magnitude of success is less known.
According to the researchers, IRS seems to be more effective at reducing malaria infections in regions with a high rate of disease and in areas where there is a threat from both Plasmodium falciparum parasites - the most deadly form of the disease - and Plasmodium vivax parasites.
In addition, the team discovered that IRS campaigns were more successful if several rounds of spraying were involved. Another factor that seemed to enhance IRS effectiveness was the use of the controversial insecticide DDT.
The researchers explained: "Our (study) results show that DDT is more effective at reducing malaria prevalence than pyrethroids or other insecticides."
Pyrethroids are the most commonly-used class of insecticides in IRS programs, however, some mosquito populations have become resistant to these compounds over the last ten years.
Due to concerns about the toxicity of DDT to humans and animals, DTT has been banned in many nations, including the United States.
According to the researchers, even low levels of DDT may still be harmful to those exposed. While DDT may be worth considering in regions where malaria transmission is prevalent, the potential health risks of DDT would need to be compared to its potential to lower malaria morbidity and mortality.
Although the effectiveness for indoor spraying suggests that mosquito control methods have "improved substantially during the past decade," the researchers state that more research is needed that examines the effectiveness of IRS and insecticide-treated bed nets (ITNs) together in order to determine whether "there is any additional benefit of combing the two in the same households."
In the second study, researchers at the University of Bamako in Mali set out to find a way to quickly detect the emergence in Africa of a malaria parasite resistant to the life-saving drug artemisinin.
Several years ago artemisinin was the most important medicine for treating malaria - partially due to the fact that parasites defeated other first-line therapies, such as chloroquine (CQ) and sulfadoxine/pyrimethamine (SP).
According to the researchers, artemisinin (artesunate) quickly killed the deadly malaria parasite Plasmodium falciparum from infected children in Mali in 2010-2011.
They found that 32 hours was the median time artemisinin took to kill the parasite vs. 84 hours in tests carried out in regions of Cambodia where the parasites are developing resistance.
Abdoulaye A. Djimde, Ph.D., with the University of Bamako's Malaria Research and Training Center and senior author of the study, said: "Our study indicates that in this region of Africa there does not appear to be any artemisinin resistance."
Christopher Plowe, M.D., MPH., a co-author of the Mali study and a malaria expert at the University of Maryland School of Medicine and the Howard Hughes Medical Institute, explained: "Whether these episodes of resistance are distinct cases that arose in isolation or related events illustrative of resistance parasites on the move has yet to be determined. Past experiences provide reason to be concerned for Africa.
Historically, parasite resistance to malaria medicines has started in Southeast Asia and then eventually moved into Africa. We have to be very proactive if we want to avoid a public health disaster in Africa, which is where most of the world's malaria deaths occur and where artemisinin resistance would have its gravest effect."
In an associated report, Caroline L. Ng and David A. Fidock, Ph.D., of Columbia University Medical Center explain that one of the reasons for such concern over the prospect of artemisinin resistance is that "we are still several years away from any other drugs being licensed and available to replace artemisinin should they fail." They state that more funding is required for studies focused on finding novel drugs.
In African clinics that serve as World Health Organization (WHO) "sentinel" sites for detecting drug-resistance, treatment involves artemisinin combination therapies or ACTs that include other malaria medicines as well.
The purpose of the combination is to make it harder for the parasite to develop resistance. However, there are some concerns that surveillance focused on ACT could delay detection of resistance emerging in Africa as other medications in the compound might disguise early signs of the parasite becoming less susceptible to artemisinin.
"We're not recommending clinics use artesunate by itself, but we need to periodically and safely conduct studies in malaria endemic regions of Africa with just artesunate if we want to detect resistance and still have enough time to intervene. I think everyone agrees that we need more surveillance on this type. The question is where do we get the resources to do more comprehensive and frequent monitoring?"
If a tell-tale genetic marker on the malaria parasite, such as the marker that reveals chloroquine resistance is discovered, it would significantly increase the hunt for artemisinin resistance.
Written by Grace Rattue