Indoor residual spraying
Encyclopedia
Indoor residual spraying or IRS is the process of spraying the inside of dwellings with an insecticide
to kill mosquitoes that spread malaria
. A dilute solution of insecticide is sprayed on the inside walls of certain types of dwellings—those with walls made from porous materials such as mud or wood but not plaster as in city dwellings. Mosquitoes are killed or repelled by the spray, preventing the transmission of the disease. In 2008, 44 countries employed IRS as a malaria control strategy. Several pesticides have historically been used for IRS, the first and most well-known being DDT
.
(WHO) recommends IRS as one of three primary means of malaria control, the others being use of insecticide treated bednets (ITNs) and prompt treatment of confirmed cases with artemisinin
-based combination therapies (ACTs). While previously the WHO had recommended IRS only in areas of sporadic malaria transmission, in 2006 it began recommending IRS in areas of endemic
, stable transmission as well.
According to the WHO:
Furthermore, for IRS to be effective:
The WHO further states that "insecticide susceptibility and vector behaviour; safety for humans and the environment; and efficacy and cost-effectiveness" are factors that must be considered when selecting an insecticide for IRS.
Few studies have directly compared the cost effectiveness of IRS directly with other methods of malaria control. A study from 2008 assessed the cost effectiveness of seven African anti-malaria campaigns: two IRS campaigns and five insecticide treated bednet (ITN) distribution campaigns. The authors found that on a cost-per-child-death-averted basis, all were about the same, but the ITN campaigns were slightly more cost effective.
With regard to the cost effectiveness of various pesticides vis-a-vis each other for IRS, historically DDT has been considered the most cost effective, mainly because it lasts longer than alternatives and therefore dwellings can be sprayed less frequently. But actual studies on cost effectiveness are lacking, and none have taken into account the adverse health and environmental effects of DDT or its alternatives. The United Nations Environment Programme
(UNEP) concluded in 2008 that "IRS with DDT remains affordable and effective in many situations but, with regard to the direct costs, the relative advantage of DDT vis-à-vis alternative insecticides seems to be diminishing. The contextual evidence base on cost-effectiveness needs strengthening, and the external costs of DDT use vis-à-vis alternative insecticides require a careful assessment."
While that stain makes it easier to check whether the room has been sprayed, it causes some villagers to resist the spraying of their homes or to resurface the wall, which eliminates the residual insecticidal effect. Pyrethroid
insecticides are reportedly more acceptable since they do not leave visible residues on the walls.
In addition, DDT is not suitable for this type of spraying in Western-style plaster
ed or painted walls, only traditional dwellings with unpainted walls made of mud, sticks, dung
, thatch, clay
, or cement. As rural areas of South Africa become more prosperous, there is a shift towards Western style housing, leaving fewer homes suitable for DDT spraying, and necessitating the use of alternative insecticides.
Other villagers object to DDT spraying because it does not kill cockroach
es or bedbug
s; rather, it excites such pests making them more active, so that often the use of another insecticide is additionally required. Pyrethroids such as deltamethrin and lambdacyhalothrin, on the other hand, are more acceptable to residents because they kill these nuisance insects as well as mosquitoes. DDT has also been known to kill beneficial insects, such as wasps that kill caterpillars that, unchecked, destroy thatched roofs.
As a result, Mozambique
's chief of infectious disease
control, Avertino Barreto, says that resistance to DDT spraying is "homegrown", not due to "pressure from environmentalists". "They only want us to use DDT on poor, rural black people," he says. "So whoever suggests DDT use, I say, 'Fine, I'll start spraying in your house first.'"
/UNEP monograph on the current status of DDT, 2008 data is from the WHO's World Malaria Report 2009, and 2009 data is from the 2010 report of the Stockholm Convention's DDT expert group. The World Malaria Report 2009 does not report the amount of DDT used in each country, only whether it is used or not. Accordingly, countries are listed as using 0 or "some" DDT.
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
to kill mosquitoes that spread malaria
Malaria
Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...
. A dilute solution of insecticide is sprayed on the inside walls of certain types of dwellings—those with walls made from porous materials such as mud or wood but not plaster as in city dwellings. Mosquitoes are killed or repelled by the spray, preventing the transmission of the disease. In 2008, 44 countries employed IRS as a malaria control strategy. Several pesticides have historically been used for IRS, the first and most well-known being DDT
DDT
DDT is one of the most well-known synthetic insecticides. It is a chemical with a long, unique, and controversial history....
.
World Health Organization recommendations
The World Health OrganizationWorld Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
(WHO) recommends IRS as one of three primary means of malaria control, the others being use of insecticide treated bednets (ITNs) and prompt treatment of confirmed cases with artemisinin
Artemisinin
Artemisinin , also known as Qinghaosu , and its derivatives are a group of drugs that possess the most rapid action of all current drugs against falciparum malaria. Treatments containing an artemisinin derivative are now standard treatment worldwide for falciparum malaria...
-based combination therapies (ACTs). While previously the WHO had recommended IRS only in areas of sporadic malaria transmission, in 2006 it began recommending IRS in areas of endemic
Endemic (epidemiology)
In epidemiology, an infection is said to be endemic in a population when that infection is maintained in the population without the need for external inputs. For example, chickenpox is endemic in the UK, but malaria is not...
, stable transmission as well.
According to the WHO:
Furthermore, for IRS to be effective:
- There must be a high percentage of sprayable surfaces within each dwelling.
- The vector (mosquitos) must feed or rest indoors.
- The targeted vectors must be susceptible (i.e. not resistantPesticide resistancePesticide resistance is the adaptation of pest population targeted by a pesticide resulting in decreased susceptibility to that chemical. In other words, pests develop a resistance to a chemical through natural selection: the most resistant organisms are the ones to survive and pass on their...
) to the insecticide being sprayed.
The WHO further states that "insecticide susceptibility and vector behaviour; safety for humans and the environment; and efficacy and cost-effectiveness" are factors that must be considered when selecting an insecticide for IRS.
Approved insecticides
Currently, the WHO has approved twelve different insecticides for IRS.| Insecticide | Class | Recommended dosage of active ingredient (g/m2) | Duration of effective action (months) | Estimated cost per house per 6 months (US$) | WHO toxicity rating |
|---|---|---|---|---|---|
| DDT DDT DDT is one of the most well-known synthetic insecticides. It is a chemical with a long, unique, and controversial history.... |
Organochlorine | 1–2 | >6 | 1.60 | II |
| Fenitrothion Fenitrothion Fenitrothion is a phosphorothioate insecticide.... |
Organophosphate Organophosphate An organophosphate is the general name for esters of phosphoric acid. Phosphates are probably the most pervasive organophosphorus compounds. Many of the most important biochemicals are organophosphates, including DNA and RNA as well as many cofactors that are essential for life... |
2 | 3–6 | 14.80 | II |
| Malathion Malathion Malathion is an organophosphate parasympathomimetic which binds irreversibly to cholinesterase. Malathion is an insecticide of relatively low human toxicity, however one recent study has shown that children with higher levels of organophosphate pesticide metabolites in their urine are more likely... |
Organophosphate | 2 | 2–3 | 8.20 | III |
| Pirimiphos-methyl Pirimiphos-methyl Pirimiphos-methyl is a phosphorothioate used as an insecticide. It was originally developed by Imperial Chemical Industries Ltd., now Syngenta, in 1967.... |
Organophosphate | 1–2 | 2–3 | III | |
| Propoxur Propoxur Propoxur is a carbamate insecticide and was introduced in 1959. Propoxur is a non-systemic insecticide with a fast knockdown and long residual effect used against turf, forestry, and household pests and fleas. It is also used in pest control for other domestic animals, Anopheles mosquitoes, ants,... |
Carbamate Carbamate Carbamates are organic compounds derived from carbamic acid . A carbamate group, carbamate ester, and carbamic acids are functional groups that are inter-related structurally and often are interconverted chemically. Carbamate esters are also called urethanes.-Synthesis:Carbamic acids are derived... |
1–2 | 3–6 | 18.80 | II |
| Bendiocarb Bendiocarb Bendiocarb is an acutely toxic carbamate insecticide used in public health and agriculture and is effective against a wide range of nuisance and disease vector insects... |
Carbamate | 0.1–0.4 | 2–6 | 13.80 | II |
| Alpha-cypermethrin Cypermethrin Cypermethrin is a synthetic pyrethroid used as an insecticide in large-scale commercial agricultural applications as well as in consumer products for domestic purposes. It behaves as a fast-acting neurotoxin in insects. It is easily degraded on soil and plants but can be effective for weeks when... |
Pyrethroid Pyrethroid A pyrethroid is an organic compound similar to the natural pyrethrins produced by the flowers of pyrethrums . Pyrethroids now constitute a major commercial household insecticides... |
0.02–0.03 | 4–6 | II | |
| Cyfluthrin Cyfluthrin Cyfluthrin is a synthetic pyrethroid derivative that is used as an insecticide in restricted use pesticide and common household pesticide. It is a complex organic compound, and the commercial product is sold as a mixture of isomers. Like most pyrethroids, it is highly toxic to fish, invertebrates,... |
Pyrethroid | 0.02–0.05 | 3–6 | II | |
| Deltamethrin Deltamethrin Deltamethrin is a pyrethroid ester insecticide.-Usage:Deltamethrin products are among the most popular and widely used insecticides in the world and have become very popular with pest control operators and individuals in the United States in the past five years. This material is a member of one of... |
Pyrethroid | 0.02–0.025 | 3–6 | 1.60 | II |
| Etofenprox Etofenprox Etofenprox is a pyrethroid derivative which is used as an insecticide.... |
Pyrethroid | 0.1–0.3 | 3–6 | U | |
| Lambda-cyhalothrin | Pyrethroid | 0.02–0.03 | 3–6 | 8.60 | III |
| Bifenthrin Bifenthrin Bifenthrin is a pyrethroid insecticide that affects the nervous system of insects.It was discovered and developed by FMC Corporation. Products containing bifenthrin include Talstar, Maxxthor, Capture, Brigade, Bifenthrine, Ortho Home Defense Max, Bifen IT, Bifen L/P, and Scotts LawnPro Step... |
Pyrethroid | 0.025–0.05 | 3–6 | II |
Cost effectiveness and efficacy
According to 2010 Cochrane review, IRS is an effective strategy for reducing malaria incidence. It is about as effective using insecticide treated nets (ITN)s, though ITNs may be a more effective at reducing morbidity in some situations.Few studies have directly compared the cost effectiveness of IRS directly with other methods of malaria control. A study from 2008 assessed the cost effectiveness of seven African anti-malaria campaigns: two IRS campaigns and five insecticide treated bednet (ITN) distribution campaigns. The authors found that on a cost-per-child-death-averted basis, all were about the same, but the ITN campaigns were slightly more cost effective.
With regard to the cost effectiveness of various pesticides vis-a-vis each other for IRS, historically DDT has been considered the most cost effective, mainly because it lasts longer than alternatives and therefore dwellings can be sprayed less frequently. But actual studies on cost effectiveness are lacking, and none have taken into account the adverse health and environmental effects of DDT or its alternatives. The United Nations Environment Programme
United Nations Environment Programme
The United Nations Environment Programme coordinates United Nations environmental activities, assisting developing countries in implementing environmentally sound policies and practices. It was founded as a result of the United Nations Conference on the Human Environment in June 1972 and has its...
(UNEP) concluded in 2008 that "IRS with DDT remains affordable and effective in many situations but, with regard to the direct costs, the relative advantage of DDT vis-à-vis alternative insecticides seems to be diminishing. The contextual evidence base on cost-effectiveness needs strengthening, and the external costs of DDT use vis-à-vis alternative insecticides require a careful assessment."
Residents' opposition to IRS
For IRS to be effective, at least 80% of homes and barns in an area must be sprayed, and if enough residents refuse spraying, the effectiveness of the whole program can be jeopardized. Many residents resist spraying of DDT in particular. This is due to a variety of factors, including its smell and the stains it leaves on the walls.While that stain makes it easier to check whether the room has been sprayed, it causes some villagers to resist the spraying of their homes or to resurface the wall, which eliminates the residual insecticidal effect. Pyrethroid
Pyrethroid
A pyrethroid is an organic compound similar to the natural pyrethrins produced by the flowers of pyrethrums . Pyrethroids now constitute a major commercial household insecticides...
insecticides are reportedly more acceptable since they do not leave visible residues on the walls.
In addition, DDT is not suitable for this type of spraying in Western-style plaster
Plaster
Plaster is a building material used for coating walls and ceilings. Plaster starts as a dry powder similar to mortar or cement and like those materials it is mixed with water to form a paste which liberates heat and then hardens. Unlike mortar and cement, plaster remains quite soft after setting,...
ed or painted walls, only traditional dwellings with unpainted walls made of mud, sticks, dung
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
, thatch, clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
, or cement. As rural areas of South Africa become more prosperous, there is a shift towards Western style housing, leaving fewer homes suitable for DDT spraying, and necessitating the use of alternative insecticides.
Other villagers object to DDT spraying because it does not kill cockroach
Cockroach
Cockroaches are insects of the order Blattaria or Blattodea, of which about 30 species out of 4,500 total are associated with human habitations...
es or bedbug
Bedbug
Cimicidae are small parasitic insects. The most common type is Cimex lectularius. The term usually refers to species that prefer to feed on human blood...
s; rather, it excites such pests making them more active, so that often the use of another insecticide is additionally required. Pyrethroids such as deltamethrin and lambdacyhalothrin, on the other hand, are more acceptable to residents because they kill these nuisance insects as well as mosquitoes. DDT has also been known to kill beneficial insects, such as wasps that kill caterpillars that, unchecked, destroy thatched roofs.
As a result, Mozambique
Mozambique
Mozambique, officially the Republic of Mozambique , is a country in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi and Zambia to the northwest, Zimbabwe to the west and Swaziland and South Africa to the southwest...
's chief of infectious disease
Infectious disease
Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...
control, Avertino Barreto, says that resistance to DDT spraying is "homegrown", not due to "pressure from environmentalists". "They only want us to use DDT on poor, rural black people," he says. "So whoever suggests DDT use, I say, 'Fine, I'll start spraying in your house first.'"
Use of DDT
As discussed above, DDT is one 12 insecticides currently approved by the WHO for use in malaria control. The following table shows recent per country use of DDT for IRS. Unless otherwise noted, data for 2003–07 is from the 2008 Stockholm ConventionStockholm Convention
Stockholm Convention on Persistent Organic Pollutants is an international environmental treaty, signed in 2001 and effective from May 2004, that aims to eliminate or restrict the production and use of persistent organic pollutants .- History :...
/UNEP monograph on the current status of DDT, 2008 data is from the WHO's World Malaria Report 2009, and 2009 data is from the 2010 report of the Stockholm Convention's DDT expert group. The World Malaria Report 2009 does not report the amount of DDT used in each country, only whether it is used or not. Accordingly, countries are listed as using 0 or "some" DDT.
| Country | 2003 use (tonnes) | 2005 use (tonnes) | 2007 use (tonnes) | 2008 use | 2009 use (tonnes) | Notes |
|---|---|---|---|---|---|---|
| Botswana Botswana Botswana, officially the Republic of Botswana , is a landlocked country located in Southern Africa. The citizens are referred to as "Batswana" . Formerly the British protectorate of Bechuanaland, Botswana adopted its new name after becoming independent within the Commonwealth on 30 September 1966... |
0 | 0 | 0 | 0 | Use suspended in 1997, plans to introduce in 2009 | |
| Cameroon Cameroon Cameroon, officially the Republic of Cameroon , is a country in west Central Africa. It is bordered by Nigeria to the west; Chad to the northeast; the Central African Republic to the east; and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Cameroon's coastline lies on the... |
0 | 0 | 0 | 0 | plan to introduce in 2009 | |
| China China Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture... |
0 | 0 | n.a. | 0 | 0 | discontinued use in 2003 |
| DR Congo Democratic Republic of the Congo The Democratic Republic of the Congo is a state located in Central Africa. It is the second largest country in Africa by area and the eleventh largest in the world... |
0 | 0 | 0 | some | plan to reintroduce | |
| Eritrea Eritrea Eritrea , officially the State of Eritrea, is a country in the Horn of Africa. Eritrea derives it's name from the Greek word Erethria, meaning 'red land'. The capital is Asmara. It is bordered by Sudan in the west, Ethiopia in the south, and Djibouti in the southeast... |
13 | 15 | 15 | some | ||
| Ethiopia Ethiopia Ethiopia , officially known as the Federal Democratic Republic of Ethiopia, is a country located in the Horn of Africa. It is the second-most populous nation in Africa, with over 82 million inhabitants, and the tenth-largest by area, occupying 1,100,000 km2... |
272 | 398 | 371 | some | 1350 | Spraying stopped in 2010 because of resistance |
| Gambia | 0 | 0 | 0 | 0 | some | plan to introduce in 2008 |
| Guyana Guyana Guyana , officially the Co-operative Republic of Guyana, previously the colony of British Guiana, is a sovereign state on the northern coast of South America that is culturally part of the Anglophone Caribbean. Guyana was a former colony of the Dutch and of the British... |
n.a. | n.a. | n.a. | some | listed in World Malaria Report 2008 as using DDT for IRS | |
| India India India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world... |
4444 | 4253 | 3188 | some | 3415 | includes use for both malaria and leishmaniasis Leishmaniasis Leishmaniasis is a disease caused by protozoan parasites that belong to the genus Leishmania and is transmitted by the bite of certain species of sand fly... |
| Madagascar Madagascar The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa... |
45 | 0 | 0 | 0 | 0 | plan to reintroduce in 2009 |
| Malawi Malawi The Republic of Malawi is a landlocked country in southeast Africa that was formerly known as Nyasaland. It is bordered by Zambia to the northwest, Tanzania to the northeast, and Mozambique on the east, south and west. The country is separated from Tanzania and Mozambique by Lake Malawi. Its size... |
0 | 0 | 0 | 0 | plan to introduce in 2009 | |
| Mauritius Mauritius Mauritius , officially the Republic of Mauritius is an island nation off the southeast coast of the African continent in the southwest Indian Ocean, about east of Madagascar... |
1 | 1 | 0 | 0 | some | |
| Morocco Morocco Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara... |
1 | 1 | n.a. | 0 | 0 | |
| Mozambique Mozambique Mozambique, officially the Republic of Mozambique , is a country in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi and Zambia to the northwest, Zimbabwe to the west and Swaziland and South Africa to the southwest... |
0 | 308 | n.a. | some | reintroduced in 2005 | |
| Myanmar Myanmar Burma , officially the Republic of the Union of Myanmar , is a country in Southeast Asia. Burma is bordered by China on the northeast, Laos on the east, Thailand on the southeast, Bangladesh on the west, India on the northwest, the Bay of Bengal to the southwest, and the Andaman Sea on the south.... |
1 | 1 | n.a. | some | 0 | phasing out |
| Namibia Namibia Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March... |
40 | 40 | 40 | some | ||
| North Korea North Korea The Democratic People’s Republic of Korea , , is a country in East Asia, occupying the northern half of the Korean Peninsula. Its capital and largest city is Pyongyang. The Korean Demilitarized Zone serves as the buffer zone between North Korea and South Korea... |
n.a. | n.a. | 5 | some | some | (an additional 155 tonnes is used in agriculture) |
| Papua New Guinea Papua New Guinea Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands... |
n.a. | n.a. | n.a. | some | unknown amounts used | |
| South Africa South Africa The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans... |
54 | 62 | 66 | some | reintroduced in 2000 | |
| Sudan Sudan Sudan , officially the Republic of the Sudan , is a country in North Africa, sometimes considered part of the Middle East politically. It is bordered by Egypt to the north, the Red Sea to the northeast, Eritrea and Ethiopia to the east, South Sudan to the south, the Central African Republic to the... |
75 | n.a. | 0 | 0 | ||
| Swaziland Swaziland Swaziland, officially the Kingdom of Swaziland , and sometimes called Ngwane or Swatini, is a landlocked country in Southern Africa, bordered to the north, south and west by South Africa, and to the east by Mozambique... |
n.a. | 8 | 8 | some | ||
| Uganda Uganda Uganda , officially the Republic of Uganda, is a landlocked country in East Africa. Uganda is also known as the "Pearl of Africa". It is bordered on the east by Kenya, on the north by South Sudan, on the west by the Democratic Republic of the Congo, on the southwest by Rwanda, and on the south by... |
0 | 0 | 0 | some | IRS with DDT was briefly implemented in 2008 | |
| Zambia Zambia Zambia , officially the Republic of Zambia, is a landlocked country in Southern Africa. The neighbouring countries are the Democratic Republic of the Congo to the north, Tanzania to the north-east, Malawi to the east, Mozambique, Zimbabwe, Botswana and Namibia to the south, and Angola to the west.... |
7 | 26 | 22 | some | some | reintroduced in 2000 |
| Zimbabwe Zimbabwe Zimbabwe is a landlocked country located in the southern part of the African continent, between the Zambezi and Limpopo rivers. It is bordered by South Africa to the south, Botswana to the southwest, Zambia and a tip of Namibia to the northwest and Mozambique to the east. Zimbabwe has three... |
0 | 108 | 12 | some | reintroduced in 2004 | |
| Global Total | 4953 | 5219 | 3725 | 4783 | 2009 use includes only India, Ethiopia, Zambia, and Mauritius |
External links
- MALARIA VECTOR CONTROL AND PERSONAL PROTECTION, WHO Technical Report Series No. 936. 2006.