Back in April, Gordon Brown appeared on American Idol in a publicity stunt to announce that the U.K. government would spend GBP£100m (US$200m)) on 20m mosquito nets to protect against Malaria. He suggested that with another hundred million or so nets could "all families could sleep safe at night". It's one of those initiatives that instinctively sounds like a good policy, but is it? A team of British and Kenyan scientists led by Abdisalan M. Noor have looked into it, and the benefits are not as clear cut as they seem [1].
Noor et al's study, published in PLoS on May 7th, looked at the prevalence of Plasmodium falciparum (the parasite that causes Malaria) infection in rural areas of southern Somalia, and attempted to find out what effect the use of "Insecticide Treated Nets" (ITNs) had in the area. It might seem obvious that mosquito nets reduce the risk of infection, but actual hard data backing this up is gappy, particularly in areas with lower transmission rates (which is a substantial proportion of Africa).
The authors note: "Little is known, however, on the effectiveness of ITN in areas of Africa that support low transmission. This hinders the accurate estimation of impact of ITN use on disease burden and its cost-effectiveness in low transmission settings." The information that we do have comes from areas where the rate of malaria infection is high - often over 40% of the population (see for example a Cochrane study on the subject [2]). In these hot spots, nets unsurprisingly have been shown to have an impact.
The point is that a policy that makes financial and practical sense in one specific type of situation (very high Malaria rates) may not do in others (medium or low rates). Without more information on this, policies like Gordon Brown's "let's spend a billion quid on nets" are basically pouring money into a problem without really understanding what impact there will be. In that situation, how on earth can you measure success, and how do you know that you're really helping much at all?
Interviews were conducted in South-Central Somalia in 2007, an area with around 1.6 million inhabitants. 201 clusters of around 50 homes were surveyed, resulting in a total of 10,359 respondents - an impressive number and one liable to give an accurate picture of the population. By asking the interviewees questions about net use and infection, they could look for patterns linking the two - the obvious expectation that areas with higher net use should see lower rates of infection.
This expectation was confirmed - overall the use of netting was shown to reduce the prevalence of Malaria by about 50%, with slight variations in river communities (48% reduction) and pastoral areas (60%), which children in particular benefitting. These figures are impressive, but not particularly interesting. The potential controversy comes when you look at the absolute rate of infection - the authors estimate that giving all 1.6 million people in the region nets would reduce infection from 17% to around 7%.
Now, that's a reduction, but as the authors point out it isn't a spectacular one, especially when you start looking at the cost. There are nearly a billion people in Africa, not to mention that these nets will need maintenance, repairs, and ultimately replacement. To be fully effective, nets have to be retreated with insecticide every 6 months - a process that's too expensive for many families. Often, the nets have more immediately value as trade goods - many nets end up being used for fishing, for example. On top of that, there are the potential health risks of sleeping under insecticide.
it's no exaggeration to say that Malaria is the scourge of mankind. It causes several hundred million cases of fever and a couple of million deaths per year, and costs African nations about US$12bn annually [3]. Mosquito nets almost certainly should be part of any solution to the problem, particularly in areas of high-transmission, but it's lazy and possibly even dangerous to assume that they're the best option without having all the facts. There's a real danger that popular, quick-fix solutions could get in the way of more intelligent, targetted efforts to attack the problem.
[1] Noor, A.M., Moloney, G., Borle, M., Fegan, G.W., Shewchuk, T., Snow, R.W., Husereau, D. (2008). The Use of Mosquito Nets and the Prevalence of Plasmodium falciparum Infection in Rural South Central Somalia. PLoS ONE, 3(5), e2081. DOI: 10.1371/journal.pone.0002081
[2]Lengeler, C., Lengeler, C. (2004). Insecticide-treated bed nets and curtains for preventing malaria. DOI: 10.1002/14651858.CD000363.pub2
[3] GREENWOOD, B., BOJANG, K., WHITTY, C., TARGETT, G. (2005). Malaria. The Lancet, 365(9469), 1487-1498. DOI: 10.1016/S0140-6736(05)66420-3
