Key to tackling malaria may lie in bed nets for adults and older children
3 July 2007
Protecting older children and adults with insecticide-treated bed nets may be an effective way to combat malaria, a study has shown.
The research, published today in the open access journal 'PLoS Medicine', suggests that protecting half of all older children and adults would also protect the wider community from malaria, which kills over one million people each year.
Current international guidelines recommend providing subsidised bed nets for young children and pregnant women in order to achieve over 80 per cent coverage in these high-risk groups. However, this strategy appears to overlook the benefits of protecting the rest of the population.
Using recently developed models of mosquito behaviour and mortality, researchers at the Ifakara Health Research and Development Centre in Tanzania, led by Dr Gerry Killeen, a Wellcome Trust researcher from the School of Biological and Biomedical Sciences, Durham University, have shown that if use of the nets can be achieved by 35-65% per cent of older children and adults, this would substantially enhance the protection of the more vulnerable groups too. Most human-to-mosquito transmission originates from adults and children over five years of age, who constitute the bulk of the population and are more attractive to mosquitoes.
"Insecticide-treated nets can protect not only the individuals and households that use them, but also members of the surrounding community," says Dr Killeen. "This is because they kill adult mosquitoes directly or force them to undertake longer, more hazardous foraging expeditions in search of blood to feed on and aquatic habitats in which to breed."
Dr Christian Lengeler, a co-author from the Swiss Tropical Institute, agrees: "Nets have an altruistic value and this needs to be considered when planning programmes."
Malaria is caused by infection with a parasite carried in the salivary glands of the mosquito. The parasite is transmitted when a person is bitten by an infectious mosquito. After a brief sojourn in the liver, it grows and reproduces very rapidly in the blood, leading to symptoms including fever, anaemia and even death. The parasites can be retransmitted to another mosquito if it feeds on an infected person.
The researchers showed that use of the nets can greatly reduce the number of mosquitoes that survive repeated encounters with protected humans. Also, by preventing the mosquitoes feeding on humans, the nets can divert them to feed on other mammals that do not host the malaria parasite, reducing the number of humans bitten and of mosquitoes carrying the parasite.
Dr Killeen and colleagues acknowledge that the financial implications of promoting net use by all age groups across malaria-endemic Africa will be significant, in the order of the total investments in health care in Africa excluding HIV.
"Fully subsidising enough nets to achieve 50 per cent coverage would cost at least $1 billion, with ongoing recurrent costs of a similar magnitude," he says. "While we need to maximise subsidies for expanded target groups, we also need to ensure those receiving little or no subsidy can buy this essential public health commodity if they wish to."
Dr Killeen is keen to stress his support for the existing personal protection targets for vulnerable groups specified by the Millennium Development Goals and Roll Back Malaria: "The targets of the existing programmes are very worthy in themselves and we remain fully supportive of their continued prioritisation. We need to cover as many young children and pregnant women as possible without forgetting that even partial coverage of entire communities can provides greater and more equitable protection to everyone."
Co-author Patrick Kachur from the Centers for Disease Control and Prevention emphasises that this is an achievable goal: "A number of African countries are making progress towards the existing targets and should be supported to attain this more ambitious goal by any means necessary. If the full potential of insecticide-treated nets, including community-wide suppression of malaria transmission, can be realised across Africa, we could prevent hundreds of thousands of deaths each year."
The research was welcomed by Dr Alex Mwita, programme manager for the National Malaria Control Programme in Tanzania.
"Malaria is still the commonest and most dangerous disease in tropical Africa today," says Dr Mwita. "In Tanzania it kills over 80 000 children annually and is responsible for 36 per cent of maternal mortality, which at 578 per 100 000 live births is one the highest in the world. Economically, malaria contributes to individual, community and country poverty through lost labour days and in expenses incurred for treatment and prevention.
"This paper is a welcome appeal to the world community to give a respite to the people of Africa, the majority of whom live in abject poverty. Free provision of at least three long lasting insecticide treated nets - which last for five years - to every household provides real chance for the people of Africa to loosen the tight grip of malaria shackles upon them."
Contact
Craig Brierley
Media Officer
Wellcome Trust
T 020 7611 7329
E
c.brierley@wellcome.ac.uk
Notes for editors
1. Killeen G et al. Preventing childhood malaria in Africa by protecting adults from mosquitoes with insecticide-treated nets. PLoS Medicine 2007. Download preview copy [PDF 502KB].
2. The research was supported by Swiss National Science Foundation, the Bill and Melinda Gates Foundation, the Biotechnology and Biological Research Council, and the Wellcome Trust.
3. Ifakara Health Research and Development Centre is an independent Tanzanian trust established in 1997. The Centre's mission is: "To develop and sustain a rural district-based health research and development resource centre capable of generating new knowledge and relevant information regarding priority problems in health systems at the district, national and international level, through research, training and services aimed at achieving better health and community development." IHRDC pioneered the development of market-based distribution systems for subsidising bed nets for pregnant women in Tanzania.
4.
Durham University
Founded in 1832, Durham University aims to provide internationally recognised research, scholarship and learning within a distinctive collegiate environment. Based on two sites in Durham city and Stockton on Tees in the North East of England, it has 15 000 students, employs 3000 staff, has created 16 spin-out companies since 2000 and has an annual turnover of over £175 million, making it the equivalent of a top 50 North-east business. The University is collegiate, with colleges providing residential, social and welfare facilities for their student members, and creating a sense of community for staff and students together.
5. The Wellcome Trust is the largest charity in the UK. It funds innovative biomedical research, in the UK and internationally, spending around £500 million each year to support the brightest scientists with the best ideas. The Wellcome Trust supports public debate about biomedical research and its impact on health and wellbeing.
6. The Biotechnology and Biological Sciences Research Council (BBSRC) is the UK funding agency for research in the life sciences. Sponsored by Government, BBSRC annually invests around £370 million in a wide range of research that makes a significant contribution to the quality of life for UK citizens and supports a number of important industrial stakeholders including the agriculture, food, chemical, healthcare and pharmaceutical sectors.
7. The Swiss National Science Foundation is the most important Swiss institute promoting scientific research. It supports, as mandated by the Swiss Federal government, all disciplines, from philosophy and biology to the nanosciences and medicine.