People tend to do quick cost-benefit comparisons of bednets vs metallic screens, and make some large mistakes. Bednets are temporary, protect only against anopheline mosquitoes which bite at night, and are used only about one-third of the time. One of the reasons for their misuse is that they are suffocating to sleep under.
ON THE OTHER HAND screens with coverings on walls or ceilings, are permanent, protect everyone in the house 24-hours a day, and protect against many blood-sucking insects as well as the ubiquitous house fly which spreads all manner of diarrheal diseases. Screens keep out Anophelines but also Culex and Aedes which bite during the day. They transmit a number of tropical diseases such as dengue. filariasis, Rift Valley Fever. Houseflies transmit pathogens from feces to food; a long list. So if we take a good look at screens from the point of health in general, and not focus myopically on malaria, bednets are a waste of time and money.
FINALLY when the walls and eaves and ceilings of houses are covered with wall paper or even papyrus, and when good screens are put on the doors and windows, and springs are put on the doors to keep them shut, the house increases in value. Also most of this work can be done by the homeowner or local carpenters.
So an accurate cost-effectiveness comparison between screens and temporary bednets should include all of these other factors. You will find that screens are a smart idea.
I use bednets when I camp out for a short time in areas where malaria transmission is intense, but I would never ask my family to live in a house in the tropics where their only protection against blood-sucking insects were a bunch of temporary bednets. So why should we expect African parents to use temporary bednets ?
Comments
Spot on
We've recently published a paper on the issue of airflow attenuation and bednet comfort here: http://www.malariajournal.com/content/11/1/200/abstract
which adds weight to Bill's blog.
We must avoid the myth that malaria will be quickly controlled
Thank you Charles and Bart for your comments:
Thank you Charles,
THERE IS A MYTH THAT THIS WILL BE QUICK. I think you are visualizing the great campaign against malaria as something we will finish in a few years, and then go on to another disease. That was true in the temperate climates, but is not true for Africa. We have been trying to control malaria in Africa for almost a century now, and it is not going away. We have to be in this for the long haul, thus permanent screens eventually become more economical. You can say that wealthy donors will provide the bednets, but they will tire of it soon. In fact right now there are few plans by wealthy donors to replace the millions of bednets that have been given out recently. So a bednet lasts 3-5 years. Then what?
BEDNETS ARE A FORM OF TORTURE. Bart has cleverly approached the problem that we all know as bednet users, it is a form of torture on a hot humid night. In Sudan once, during the rainy season, the head of our malaria program went to an upcountry wedding, which traditionally lasted for 3 days and nights. Rather than sleep under a bednet and suffer, he slept on a cot outdoors. Yes he got malaria - which shows how much even knowledgeable people will try to avoid the hot humid bednets. At least with a screened house you have some hope of cross-ventilation and a little breeze.
CULEX AND AEDES BITE DURING THE DAY. Another point to consider in economic comparisons is the value of house screens to protect against pest mosquitoes, which may not transmit diseases. You find this frequently in rice-growing areas where double or triple cropping is practiced. This creates hordes of Culex mosquitoes which drive people crazy. Bednets offer some protection at night, but these critters bite all day long. House screens are much better.
Bill
William Jobin Director of Blue Nile Associates
Theoretically I love the idea
Theoretically I love the idea of screens but practically I think its a very different thing. People living in a rural village don't usually sit around the house all day - and just like with bed nets, screens only work if the person is inside the house. Also the practicalities of getting people to completely screen every tiny opening in a bush house, and repair any holes, is a huge task.
Why screening houses is more cost-effective than bednets
I realize how lacking our understanding is of housing situation in Africa. It is true that there are a few nomadic communities who have no permanent settlements but they have shelters anyway. The notion that houses in Africa are "bush houses" with holes all over is wrong and a misleading one. There are many permanent settlements and even very modern houses in tropical Africa.
I embrace the idea of house screening as a strategy for malaria control in Africa. I am convinced that insect proof houses will take us beyond where we stand today with LLITNs. The current challenges facing the use of ITNs are great and can't be just ignored. We have with us insecticide resistance which is getting worse by the days, the challenge of achieving universal coverage and the trouble of ensuring daily nightly use with the implementation of ITNs. One solution to all these is house screening with a material which has no insecticide it.
Many still seem to question how screening is possible in Africa, and I answer in saying , 'It is very possible.' I am currently working on a house screening project. We just finished on a training to figure out how to install the eave screens in typical African houses and the results so far are impressive. Read my experience when I visited the seven houses we just screened for a trial; http://malariakenya.blogspot.com/
We have great ideas of what we ought to do, the only thing that remains is to get down and work. If we ever wait for anyone to initiate the house screening work other you in MW then it might never be done. If we embrace this strategy, then lets get to work and tell the world what we have done, who knows, with evidence of our achievements many will see how possible house screening is in Africa.
Bernard
House screening ad other aspects of IVM
When carrying out a 6 village trial we added screens to the eaves,windows and doors of houses in one village, but also did one 'barrier' spray on vegetation around these houses. Exit trap data showed that we succeeded in reducing the influx of mosquitoes into the houses. The cost of screening in one year was higher than IRS or supplying a net, but with care the screening should last far longer. Unfortunately the government in Cameroon has only distributed bed nets and may have recently done some IRS, but there has been no advice given to communities to educate villagers on the importance of blocking holes where they occur in walls or screening their houses. Much could be achieved by villagers, if encouraged, to improve their houses and suitable materials made available in the rural districts. However, where biting occurs outside houses, spraying around latrines outside houses may also be needed to protect adults if they are out at night - and/or the availability of repellents and advice on how drainage within the village can reduce mosquito populations.
Quality of houses does vary, but I have seen many houses with large gaps in the walls, that could easily be blocked up with mud perhaps with some netting from a damaged bed net.
G. Matthews
Comparing screening with an annual spray with ICON
To wind up this lively discussion, I would especially like to thank Bart, Graham and Cliff for their contributions. For Cliff and Graham who are doing screening and house improvements in East Africa, I would like to offer some recent cost data that I developed from the US Presidential Malaria Initiative and their 15 countries. The latest numbers I have for their spray operations with the pyrethroid ICON is that it costs over USD$7 yearly per person protected, in 2010 (see "IMPROVEMENTS IN THE US PRESIDENTIAL MALARIA INITIATIVE 2012" - Blue Nile Monograph Three - available on Amazon.com next week).
So what does this mean in a household of 5 people who might like to screen and improve their house instead? The numbers are easy, it would mean they could spend $35 per year on screens. In 10 years they could invest $350 in improving their house.
How does that compare with the costs you see in your East African projects? I know it is not a comparison with bednets, but at least it would tell us where screens rank, among the 3 possibilities.
And of course at the end of 10 years investing in screens, you have a permanent improvement in your house. Whereas with bednets you are left with tatters, and with ICON you are left with just a faint whiff of the biocide.
Thanks for all of your comments. Someday we are going to lick this!****
Bill
William Jobin Director of Blue Nile Associates
Cost-effectiveness of bed nets versus screening
I would be very interested to see a cost analysis of bed nets versus screening. The distribution of bed nets and the monitoring of their use is a significant logistical challenge in itself but to screen every hut in every village in the malaria endemic regions of Africa....
In order to ensure that the screening was done correctly, you would need to have large teams of trained personnel to install the screening and to follow up with checks and repairs. I don't think that one could leave the householders to install the screening to mosquito-proof their dwellings.
Porches in the USA also cost money
Dear Graham,
Why, when it gets to Africa, is the issue always 'cost-effectiveness' and should 'we' get away with minimal expenditures to alleviate the problem? I am sorry, but I fail to see this. Getting rid of malaria on a shoestring has not worked anywhere before in history, so it will cost - big time.
But let's take one step at the time. Why not select an appropriate region and see if a few villages are interested in screening. Why not provide a microcredit to an interested local entrepreneur to undertake this effort and provide the service of screening the houses at reasonable cost? If it kicks off there will be no need for donor funds. And, as Bill says, for people to get rid of the Culex nuisance may be a bigger incentive to go for screening than actual malaria control.
Turn malaria control into business and we may see a different world...Let's not forget, there was no cost-effectiveness study when the south of the US massively adopted porches to protect against mosquito bites, right? People wanted it, because it worked (and still works), and the cost was (is) secondary.
Best,
Bart
Screening in Kenya
Ned Walker and others are launching a screening effort in a village in Western Kenya, near Kisumu. Other Kenya researchers have shown the effectiveness of ceilings made of local materials. This project focuses on eaves. Here is a blog related to the project:
http://malariakenya.blogspot.com
Cliff
Cost-effective malaria control
Hi Bart, When discussing cost-effectiveness, I don't necessarily mean the cheapest interventions - there maybe interventions that cost more to implement but deliver a relatively greater impact in terms of malaria control than cheaper alternatives and, therefore, prove more cost-effective. However, realistically we have to realise that, despite the huge increase in funding for malaria control in recent times, money and resources are still limiting. Therefore, to ignore cost-efectiveness would, I think, be a mistake.
Monitoring screens vs bet net use
It is easier to examine a house for screening than to monitor bed net use. One does not need to enter the house, observe household behavior at night, or trust self reporting. One just walks around the outside of a house and looks at the condition of screens placed in the eaves. That is easy. Other barriers, such as doors and windows can be observed from the outside.
Cliff
Suppression of malaria has to be a program, not a short project
To Graham and some of the other commentators:
Thanks for your comments and insights. I need to make several responses. ONE Yes I have done this myself in the steaming tropics and in the semi-desert tropics. I screened our house in Puerto Rico where we lived next to a large coastal swamp and were exposed to dengue fever epidemics. Then I screened our house in central Sudan in the hottest foci of malaria transmission that I have ever seen. In Sudan we eventually stopped taking prophylactic drugs and relied entirely on the screens. Needless to say that there were a lot of other mosquitoes and vector borne diseases in Sudan besides malaria. But the screens worked. TWO Graham, please do not envisage screening as a centrally managed project which tries to screen every house in Africa in 3-5 years. The fight against malaria in Africa will take a lifetime. Screening of houses should be done on a methodical and progressive basis, covering decades. As MOH assistance starts to impact the endemic areas, people will start screening their homes on their own, because of the obvious benefits. THREE Yes, we need to do a good cost-effectiveness comparison of screens vs bednets. Are there any economists willing to try? FOUR Yes covering all the holes in roofs, eaves and walls is difficult. People have approached this by putting in a false, paper ceiling, which takes care of all the holes and corrugations in the eaves. In Tennessee and in Rwanda it has been done with wall paper and with papyrus. FOUR Malaria has been around for thousands of years. Why does anyone think a few years under bednets will defeat it?
Bill
William Jobin Director of Blue Nile Associates
Airflow attenuation
Yes Bart, http://www.malariajournal.com/content/11/1/200/abstract is a very nice article showing that nets hinder air flow making them likely hot and stuffy in the absence of a fan (e.g. http://www.malariaworld.org/content/solar-net-fan-potential-tool-enhance-bednet-usage-hot-climates). But is there any reason to assume that screening houses with fine mesh does not attenuate airflow and makes houses hot and stuffy?
screening
I would wish for some kind of double screen, which would serve as a trap as well. Insects could fly through the outer layer, but not the inner. The outer layer would be such that the insects could not go back outside again. With smell, CO2 coming from inside the house itself would be a gigantic insect trap.
Is screening a practical malaria intervention?
I agree that in the long run, screening is a better intervention than bednets (It was a major factor in eliminating malaria in the US), but I am not sure that it is a short-term answer to malaria control at the national level.
The key to malaria control is universal use. While individual LLINs provide considerable protection for the individual sleeping under it, only near universal coverage of all sleeping spaces will result in the lack of human blood meals which will cause the reduction of Anophelines populations, leading to reduced malaria transmission. (Or cause them to change their feeding habits. If mosquitoes move to feeding on non humans - such as cattle - the transmission of malaria is interupted. If they move to out door or early or late feeding on humans, malaria transmission may not be interrupted. Both behavior changes have been reported due to LLIN use.) Universal screening would probably produce the same results. After all, significant populations of Anophelines live in the US, but mainly feed on non-humans.
Malaria is a disease of poverty. Malaria is not common where everyone has screened or airconditioned houses. However, it is much cheaper, and easier, to mass distribute LLINs than to ensure screening of every house in Africa (or eliminate poverty). While screening houses can (and should) be encouraged through communication interventions and maybe tax or other incentives, a universial LLIN strategy can lead to immediate reduction of malaria, and when coupled with other interventions, to malaria control and possible elimination.
We can expect almost every African to use a bed net, if the nets are provided and promoted appropriately, Africans don't want to see their children sicken and die any less than anyone else. But we can't expect every African to be able to afford to screen, and maintain their house, at least in the short or medium time.
Charles Llewellyn
charles.llewellyn@gmail.com
Is screening a practical malaria intervention?
I would be interested to understand what contribution an unused LLIN simply left handing in a corner of the room would contribute to vector control. If people are refusing to use them, as they often do, then maybe we can at least encourage their hanging in specific areas of the dwelling, i.e. nearer eaves and windows, rather than stored away under a bed or left in the bag.
Clearly, improving housing plays a huge role in preventing biting, but that also implies a degree of economic development too - the virtuous circle that you would wish for. Interestingly for me being in the industry and company that I am, boosting rural incomes through better smallholder farming could go a massive way to achieving this as - as usual the story is very complex and not as simple as one intervention for mosquito control over another (but then we all know that).
Mark Birchmore | Head of Vector Control, Syngenta
screens and bednets
dear Bill
It is not clear from what you write if you actually tried out what yu describes ?
We did. Our experience became that screening a house with PVC covered net (nearly as good as the metallic net you suggest) needs to be done very, very thorougly to work. Ina house with a corregated roof, every opening in this folded structure had to be covered to avoid moquitoes to get in. Then we replaced the PVC net with a PE net material with deltamethrin incorporated and found that we could be a lot less thorough and it worked better than the PVC net. We included doors and windows with overlapping net, and it worked (we now know it worked for years). However, the door screen did not, the net curled up and we tried a permethrin holding thick yarn net and it was even worse, we tried agro nets from the market (they are woven opposite to bednet matreial that is knitted), same problem though slower to develop.
Over the years, a second problem appeared. People replaster their walls, because they are neither termite nor rainproof, and surely not to floods. We found that betwen25 and 30 % of people remade their walls per year, so any structure covering the wall would have to be removed and people are not very good in putting it back. Big problems for wall lining, less of a problem for eve nets that are fixed on wood struture outside the walls.
People happy with their eve nets often stop using their bednets. If door net and window nets are also in place and used with discipline, no problem, they are well protected - but if not, the personal protection is gone because mosquitoes entering the house will go and bite before going to rest on walls.
So, the real question is, will such products as eve nets and wall lining that demand a bit less discipline than bednets and probably last longer (the door problem untold), give less or more transmission in real life situations?