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Why screening houses is more cost-effective than bednets

August 1, 2012 - 15:50 -- William Jobin

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

Bart G.J. Knols's picture
Submitted by Bart G.J. Knols 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.

William Jobin's picture
Submitted by William Jobin on

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

Submitted by Guest (not verified) on

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.

Submitted by Guest (not verified) on

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

Submitted by Graham Matthews on

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

William Jobin's picture
Submitted by William Jobin on

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

Ole Skovmand's picture
Submitted by Ole Skovmand on

we ran a study wuth eave nets in Western Kenya, in a hot and humid area. To be accepted by ethical commitees, we tested bednets alone and bednets+ insecticide treated eave nets+curtains+door hangers. We used pyr spray to see entomological impact. Eave net houses had 70 % less Anoephels mosquitoes and even fewer blood fed than bed net houses. The eave nets were very popular and families told us that when visiting neighbours in the evenings, house with eave nets were chosen because there were fewer mosquitoes. After 4.5 years, around half the eave nets were still there contrary to 4 out of 200 bednets (we covered all sleeeping places). We thena sked people how much they would pay for the nets and the amount would cover the costs. Then we asked them how much they would pay to have them set up, and the amount would not cover the costs. Finally, we asked them how much they would ask for to install in the vllage, and that was more per house than they were willing to pay themselves. These PE nets are much cheaper than a metallic net, and it does not help that a metallic net will last longer, because most of the lacking nets were not there because the house was gone, rebuilt or he owner dead. So, eave nets are much better than bed nets, cost less over 4 years, but still needs donor back up. Only bed nets get donor back up

Graham Small's picture
Submitted by Graham Small on

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.

Bart G.J. Knols's picture
Submitted by Bart G.J. Knols on

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

Cliff Landesman's picture
Submitted by Cliff Landesman on

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

Graham Small's picture
Submitted by Graham Small on

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.

Cliff Landesman's picture
Submitted by Cliff Landesman on

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

William Jobin's picture
Submitted by William Jobin on

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

Ole Skovmand's picture
Submitted by Ole Skovmand on

we trained a local team to segt up eave nets. It took half a day. they were armed with staple guns, a ladder, a Hammer, nails, 3 men (or two men and a woman) per team and after the first day and corrections, could set up eave nets in a house in around 30 min. 2 of these did the eave net, the third did Windows curtains and door hangers. Door hangers (either net or or lamels, both treated) and curtains did not prevent Culex to enter and Anopehels are told to go by the eaves, and they were kept out . You would need a technician supervisor for say 5 teams, and in operationel costs, it is cheaper than IRS because you need no cleaning stations and all the extra costs around handling toxic materal and keeping pumps working. You bother people less, they do not have to move out furniture and stay out for hours. So, if you use the IRS teams - not to create a problem of what to do with these people - to put up eave nets, the material cost wll be a bit higher, the effect will be much longer, and they can work all year round and not just as seasonal workers, since the nets will last many seasons
the probem is the donors, not the efficacy of the Tools or the costs

Submitted by Olivier Briet on

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?

Submitted by Guest (not verified) on

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.

Submitted by Charles Llewellyn on

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

Mark Birchmore's picture
Submitted by Mark Birchmore on

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

Ole Skovmand's picture
Submitted by Ole Skovmand on

dear Marc, we tried that in a different way. To target 5-14 years old kids that rarely use bednets (see WHO statistics) we tested in two set up an A-shaped bednet that hang from a string and thus could be pushed over a temporary sleeping site on straw mattress in the middle of the room in night time, where these kids sleep in most houses. In daytime, pushed to the wall, thus hanging. After some months, we returned to these houses, most the nets were removed. Most of these that were stll present and told to be in use, were packed in the original bag and haging on the wall or in a locally made bag, also hanging on the wall. The reason was - we were told - it is not decent to have a bednet hanging in the living room in daytime. So, i do not think your idea would work, but if you made it into a nice textile, it would evaporate sufficient insecticide to kill entering fully suscpetible mosquitoes at least for some weeks (we tried that in the "mosquito hotel" in Kisumu with Michigan state University)
and I fully agree on your final sentence that it is very complex and all simple, one-go golden solutions are wrong

Submitted by Guest (not verified) on

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?

Ole Skovmand's picture
Submitted by Ole Skovmand on

this is rght. We also tested untreated PVC covered nets, and to obtain good protection, we had to fill every (every) entranes along the roof inclding the folds in the corrugated roof and it took more than a day per house. Contrary to that, an insecticide terated net (pyrethroid) did not need a perfect set up to work better; a metallic eve net will of course be the same, and it will be hard to fit to a corrugated roof; strong PE nets treated with insecticide last for many years, only few were gone after 4.5 years because of net damage, most were gone because of detachments (cats slept in the eave nets and the houses with heavy cats or several, the cats detached the stapples or the staples cut through the yarns) , the rest were house removed or rebuilt to be expanded. In he middle of our project, we learnt about the cats and amplified the net fixing with nails to timber carrying the roof.
The replastering was not a problem, since we knew that and fixed the net to timber Under the roof and on top of the walls. All houses had interior walls renewed every year or at least every second year, and that was only in one case out of 40 houses the reason for net removal and only after 4 years (so, after several wall replasterings)

Andrew Lover's picture
Submitted by Andrew Lover on

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0062769;jsessionid=F285E38650220D1946DFA16C996E6108

The Anopheline IRR = 2.35, 95% CI: 1.30–4.23, P = 0.005). At the lower end of the CI, 30% reduction isn't massive, but good to see some solid evidence.

Andy Graham's picture
Submitted by Andy Graham on

I am living in Kara, Togo, most of the homes are concrete construction, with many types of window. I have marked off a 3 x 3 block area around my apartment. We will collect videos, data of the type of windows and door screens, bed nets etc. for this 3 x 3 block defined area. The cost of putting plastic screens on a window is about 1 dollars per square meter of screen, 1 dollar for strips of wood lathe, and another dollars for installation. 3-5 dollars per window. If I assume that each home has 3 windows, (I believe it to be only 1.5 per house,) then the cost per home is 15 dollars They sell UNICEF bed nets in the pharmacies here for 3700 CFA or 8 dollars. All this is speculative now, except the material cost.

We have these neighborhood money-lenders, and micro-finance people who could lend the money to people for the window screens.

Presently, there is no inventory of the wood lathe needed to install a mosquito screen on a badly designed window. Therefore, to put screens on the window means I have to buy the board, then have it cut. Therefore, with the helps of a couple locals construction men, we will stockpile wood lathe, screen, nails, screws, etc and have them go out and sell the screens.

Please note, I know I am ignoring the need for door screens at this moment.

Andy Graham

Thank you, Andy Graham working on eradication of malaria in Kara, Togo West Africa. Togo Cell: +228 9294 0714 Benin Cell: +229 9559 6685 USA Skype: hobotraveler.com

Submitted by Daniel Kyabayinze (not verified) on

I also want to believe that we can do more in preventing vector-human contact with improved housing. As housing standards in some African countries improve, the burden of Malaria starts to go down ( houses have screens). But your statement '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' comes from a more privileged household that has means to choose where to live and pay for other preventive tools. Unfortunately that choice is not possible for most families, and they can only wait for a donor to provide ( most cases what the donor thinks is affordable or is the priority for funding). Everyday I live in the community ( here in Uganda) with families being bitten by blood sucking insects.

William Jobin's picture
Submitted by William Jobin on

I humbly agree Daniel. Since the donors include the US Presidential Malaria Initiative (PMI), we should try to convince them that they would better invest in screens, instead of blanket indoor spraying, year after year. There is little word out of Washington yet about continuing the PMI, but I am hopeful.
Bill

William Jobin Director of Blue Nile Associates