Tens of thousands of children’s lives have been saved in Africa, largely thanks to the rapid scale-up of four safe, effective malaria interventions―made possible by dramatically increased funding starting in the early 2000s.
Still, too many children are dying―about one every minute―and the fight against malaria is far from over. Worldwide an estimated 655,000 people died of malaria in 2010. Most of them were young children in Africa.
The global malaria community no longer articulates “control” as the goal. The goals are now elimination in individual countries and eventually global eradication.
Over the last two decades, CDC has helped develop and evaluate all four of the current interventions: insecticide-treated bed nets (ITNs) and indoor residual spraying (IRS) to protect families from mosquitoes, accurate diagnostic tests and high-quality effective drugs, and preventive treatment for pregnant women so that they are protected and their babies are born healthy. Now CDC is developing effective strategies for using and evaluating new interventions to fight malaria. CDC is also boosting its efforts to monitor and evaluate approaches to the growing problem of resistance to drugs and insecticides, as well as investigating new ways to collect the strategic information needed to track progress in the fight against malaria.
Can these four interventions drive malaria deaths down to zero? Judging by the efforts of the global scientific community, the answer is no—at least not everywhere. Government agencies, academia, nongovernmental agencies, pharmaceutical manufacturers, and multiple others are busy looking for tomorrow’s tools, ranging from medicines and vaccines to transgenic mosquitoes—some of which may soon be available.
Until more effective new tools are ready, the tools currently available must be used as wisely and effectively as possible.
Making the best use of current interventions
CDC recently took a closer look at two effective mosquito control interventions: ITNs and IRS. Both prevent transmission from mosquito to person by repelling or killing the mosquitoes that spread malaria. Because most mosquitoes that spread malaria bite people at night, an insecticide-treated net hung over a sleeping space at night succeeds in reducing transmission. ITNs have been successfully scaled up nationally in most countries and have played a major role in decreasing malaria cases and deaths. IRS―a long-acting insecticide sprayed on a home’s indoor walls―also takes advantage of mosquitoes’ preferred habits. After taking a blood meal, the full, heavy mosquito finds a place to rest, typically on the inside wall of a home. Until recently, IRS had typically been used in areas of seasonal malaria transmission and epidemic-prone areas where it can be applied at most once annually. IRS is resource-intensive and requires well-coordinated, well-trained spray teams, making it extremely difficult to scale up nationally. Furthermore, because most insecticides used for IRS remain effective for less than a year, IRS has not been used routinely in areas where malaria transmission occurs year-round, and where IRS might need to be applied more than once a year.
IRS + ITNs = ?
Can we use the two together in areas of year-round malaria transmission, which is typical of most of the countries in Africa with the highest malaria burdens? Can we drive down malaria transmission even further by using the two interventions together?
CDC conducted a study to answer these questions. Investigators took advantage of an IRS campaign conducted by the Kenya Ministry of Health in Rachuonyo District in 2008 and 2009. Soon after the campaign, the study provided a brand-new ITN for every sleeping space in Rachuonyo District, as well as in Nyanza District, which was not reached by the IRS campaign. People were encouraged to give up their older ITNs in exchange for a new one to make sure they were all using equally effective, durable nets. During the study, participants were visited monthly and encouraged to come in to the clinic when they were sick. The houses were monitored for mosquitoes and entomologists measured the numbers of anopheline mosquitoes, the species capable of transmitting malaria, as well as the effectiveness of the insecticide.
Participants who received both interventions, IRS and new ITNs, had a 62% reduction in malaria infection (parasitemia) compared with participants who received new ITNs but who did not live in the district where IRS was applied. The combination protected the most vulnerable―very young children 6 months to 4 years of age―especially well. In that age group, infection was reduced by 67%.
The IRS campaign was effective in reducing numbers of anopheline mosquitoes and in killing mosquitoes throughout the study. At the end of the study there were fewer anophelines in the district receiving IRS. These data suggest for the first time that by using both interventions together, people living in areas that receive both interventions benefit considerably.
Now that this study has shown such promising results, CDC epidemiologists are looking forward to answering the next related question—whether the use of both interventions together can delay the spread of insecticide resistance. Currently, all ITNs use a class of insecticide called pyrethroids. Unfortunately, insecticide resistance to pyrethroids has been documented in many places. One hypothesis CDC scientists are testing is whether the spread of pyrethroid resistance could be delayed or averted by using ITNs with pyrethroid insecticides together with IRS using an alternate insecticide class.
With evidence like this, and more accumulating in laboratories and field trials each day, we hope soon to be using the next set of tools, or the best combination of current tools, to reach zero.