A new study by the Institute for Health Metrics and Evaluation (IHME) at the University of Washington shows that insecticide treated bed nets (ITN) have a dramatic effect on child mortality due to malaria, reducing it by 23%. The study, “Net benefits: a multi-country analysis of observational data examining associations between insecticide-treated mosquito nets and health outcomes,” was published in PLoS (Public Library of Science) Medicine recently. The results of this study confirm that children who live in households that own at least one insecticide-treated bed net are less likely to be infected with malaria and less likely to die from the disease. The paper is focused on Africa, but the findings apply to all regions that have a significant malaria risk.
This study is part of the ongoing work by IHME (which is an independent global health research centre and provides rigorous and comparable measurement of important health problems and evaluates the strategies used to address them) to calculate the impact of malaria in terms of death and injury and to measure the impact of interventions to prevent and treat malaria.
Malaria is spread through mosquitoes that primarily bite at night, and sleeping children are particularly vulnerable to death from a malaria infection. IHME researchers, in collaboration with researchers at the University of Zambia, examined data from 29 demographic and health surveys and malaria indicator surveys routinely collected since 2000 in 22 sub-Saharan African countries, to test the health outcomes of household ownership of ITNs. They found clear evidence that scale up of net coverage was associated with a substantial reduction in childhood mortality and in parasitemia prevalence.The results show that at least one ITN household possession is associated with a 20% significant reduction of infection with the malaria parasite (from 7 surveys in 7 countries) and a 23% significant reduction in all-cause child mortality (from 29 surveys in 22 countries). These results were consistent across a range of malaria transmission settings and across countries with disparate levels of ITN household coverage. They are also consistent with data from earlier smaller-scale studies that have shown ITNs to be associated with significant reductions in malaria under program conditions.
The analysis suggests that expanded ownership of bed nets could lead to even more health gains in sub-Saharan Africa. The ITN provides individual protection to the person sleeping under it from infected mosquitoes; the insecticide kills mosquitoes that spread malaria, thereby reducing the overall propensity for transmission in the community; and if the person under the net is already infected with the malaria parasite, the ITN prevents them from infecting mosquitoes and leading to more transmission.
In a candid interview given to CNS (www.citizen-news.org), the lead author of the study Dr Stephen Lim, Associate Professor of Global Health at IHME, said, "We looked at the effect of ITNs on child mortality and malaria parasite prevalence in those household that own them. It is difficult to say whether ITNs reduce child mortality by the protection of children, or by eradication of mosquitoes by insecticide. However our results definitely show that ITNs reduce the prevalence of malaria. We were not able to examine whether there was a difference between simply owning an ITN or using an ITN in our study, but other studies suggest that efficacy of treated nets does depend upon duration of use and how they are used, e.g. people sleeping under ITNs makes a difference in their effect. In our study we examined only the household protective effect and did not examine community level effects. There is not a lot of evidence that quantifies the community effect versus the individual effect of ITNs. But we can certainly say that ITNs reduce child mortality with the overall effect being a 23% reduction in child mortality (from one month to 5 years of age)."
“Most of the studies that have examined the relationship between bed nets and health outcomes have been limited to a handful of countries,” said Dr. Lim. “We now can say with confidence that bed nets reduce mortality substantially and that the efforts to distribute these bed nets across the region are working.”
Although the study provides robust evidence of the efficacy of ITNs in reducing malaria parasite prevalence, incidence, and all-cause child mortality from carefully conducted trials in sub- Saharan Africa, ITNs are not the sole answer to malaria control, as they cost money and need to be continually replaced when they wear out. It is also largely unknown if ITNs concentrate the vector flies on those people who do not use bed nets, thus increasing the incidence of infection among people without bed nets while decreasing it for people who use them.
Scientists have been engaged in an ongoing debate about the effectiveness of ITNs. While clinical trials have shown the efficacy of ITNs in controlled settings, less is known about their impact in real world conditions, where the nets may be torn as they age or not retreated with insecticide as needed to be effective. While further work is needed to elucidate possible variations in the effect of ITNs, these findings do add to the body of evidence that ITNs are effective when used routinely, in reducing infection and death from malaria. By showing that ITNs work not only in theory but in real world conditions, the study suggests that expanded ownership of ITNs could lead to even more health gains in sub-Saharan Africa.
The next 5 to 10 years will be critical in the fight against malaria. Case studies of countries where bed net scale-up has been successful could help inform policies to increase coverage in other countries.
As Dr Lim and his colleagues suggest, continued scale-up of long-lasting ITNs (LLINs) will save more lives. LLINs typically wear out after 2–3 years and the malaria control community will have to find efficient ways of replacing worn out nets once high coverage has been achieved. So new testing new tools will have to be focussed upon to achieve the next level of malaria transmission reduction beyond what is achievable by high ITN coverage alone.
(The author serves as the Managing Editor of Citizen News Service (CNS). She is a J2J Fellow of National Press Foundation (NPF) USA. She has worked earlier with State Planning Institute, UP and taught physics at India's prestigious Loreto Convent. Email: email@example.com, website: http://www.citizen-news.org)