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Insecticide treated nets--technological & operational challenges.

Mosquito nets treated with pyrethroid insecticides repel, disable and/or kill mosquitoes on contact. They provide personal protection to individual users, but when used by a high proportion of people in a community they have been shown to avert around haft the number of malaria cases (1,2). Collateral benefits of using insecticide treated nets (ITNs) include protection against nuisance of bed bugs, head rice and so on. A number of evaluations of the efficacy and effectiveness of ITNs have led to their use for prevention and control of malaria in different settings all over the world including India. Sahu et al (3) in this issue presented results of one such study in a malaria endemic area of India to show the considerable protective efficacy of insecticidal treatment of nets, especially with use of micro-encapsulated formulation than an emulsifiable concentrate formulation. The efficacy was superior with endophilic vectors and relatively lower with zoophilic species, and ITNs reduced malaria incidence markedly with nearly two-thirds of nets still usable after one and half years of routine community use. This study therefore adds another piece of evidence in favour of ITN technology which is undergoing considerable improvement.

Many cultures in Asia have a long tradition of using mosquito nettings. Nets made up of a number of fabrics such as polyester, nylon, polyethylene and cotton are available commercially. With the development of the technology of treating nets with low dosage of pyrethroid insecticides, it has been possible to facilitate treatment of nets owned by people, as well as provide ITNs to socio-economically underprivileged societies often living in geographically difficult-to-reach areas with high malaria burden. For a number of technical and operational reasons, polyester nets have been found most suitable for treatment with a pyrethroid insecticide. Nets should be treated at least every six month intervals in areas with year round malaria transmission, or more frequently if they are washed more than two times in six months; they should be treated at least annually once just before the beginning of transmission season in low malaria endemic areas.

In Africa, so far the focus has been on targeting children <5 yr and pregnant women, but in Asia ITNs are being promoted for whole population at risk or low socio-economic groups in such populations to begin with. In India, since mid-1990s the National Vector Borne Disease Control Programme has been providing ITNs and/or net treatment in more and more malaria endemic areas (2), and expectant mothers as in Gujarat State (Prajapati PB, personal communication).

Millions of ITNs are required to achieve high coverage of populations living in malaria endemic areas. In the context of Asia, and more particularly India, this task has beset with challenges such as lack of a true assessment of at-risk populations or determination of ITN-target population, low ITN re-treatment rate and inadequate ITN coverage rate in target populations, lack of large resources required to scale up coverage, indecision on choosing various ITN delivery mechanisms such as whether to distribute ITNs free, subsidized or using cost-recovery strategies. Besides, lack of evaluation of operational 1TN programmes using standard survey methodologies in many countries has led to absence of a proper operational guidance. For example, a household survey in India reported a low ITN coverage rate despite a decade old ITN programme (4). To accelerate use of ITNs for personal protection, a common person's dilemma is where to get their nets treated or buy a treatment commercially.

With the development of technology of long-lasting treatment of nets, the sit, ration has improved on a number of counts. A long-lasting insecticidal net (LN) is a "factory-treated mosquito net with insecticide incorporated within or bound around to the fibres, or a mosquito net treated with a long-lasting insecticidal treatment kit, which retains its biological activity for at least 20 WHO standard washes under laboratory conditions and 3 years of recommended use under field conditions without re-treatment." (5) An LN therefore requires no more insecticidal treatment during its recommended life of 3 or 5 years for different brands. Although industry is developing or improvising existing LN technologies, the WHO has so far given full recommendation for one LN brand and interim recommendation for four LN brands and an LN-treatment kit that can be used for long-lasting treatment of ordinary polyester nets at home (6,7). Evidence from field of the persistence of insecticidal effectiveness ([greater than or equal to] 95% knockdown rate or [greater than or equal to] 80% mortality) indicates that the useful life of Olyset[R] LN is for 5 years or more(8), and that of PermaNet[R] 2.0 it is for more than three years(9). Similar evidence is awaited for other recent LN brands.

Quality control of LNs and LN-treatment is an important operational issue. Use of various brands of locally available soaps for washing LNs may result in variability in long lasting insecticidal effect. Therefore, for quality control monitoring purposes under field conditions, there is a need to further work on standardizing existing washing procedure (10). The available LNs use either coating or incorporation technologies. The need for reviewing and improvising LN test procedures and understanding retention/release of insecticides from LNs through successive washes has already been recognised (7).

A number of operational and implementation research issues should be addressed. The operational impact of insecticide resistance on the efficacy and effectiveness of ITN/LN interventions is not yet fully understood. This requires building medical entomology capacity and monitoring insecticide resistance especially in areas targeted for ITN/LN interventions. In Indian context, it is important to evaluate long-term field performance of LNs, especially assessment of community acceptance and coverage rate, epidemiological impact and attrition rate. A number of recent studies have evaluated wash resistance of certain LNs using local detergents (11,12). For making global comparisons, such wash resistance studies should also use WHO standard washing procedure and well characterized sensitive reference mosquito strains (10).

To realize full potential of ITN/LN technologies, the LNs should be scaled up to achieve full coverage of all population groups in areas where these are the chosen method for malaria prevention. This will require free or highly subsidized distribution of LNs. A strong managerial approach will be required to implement an LN programme by malaria programme managers. (13)

References

(1.) Clarke SE, Bogh C, Brown RC, Pinder M, Walraven GEL, Lindsay SW. Do untreated bednets protect against malaria? Trans R Soc Trop Med Hyg 2001; 95 : 457-62.

(2.) Yadav RS. Insecticide treated nets for control of malaria in South-East Asia. Unpublished Document, New Delhi: South-East Asia Regional Office, World Health Organization; 2005.

(3.) Sahu SS, Vijayakumar T, Kalyanasundaram M, Subramanian S, Jambulingam P. Impact of lambdacyhalothrin capsule suspension treated bed nets on malaria in tribal villages of Malkangiri district, Orissa, India. Indian J Med Res 2008; 128 : 262-70.

(4.) In-depth review on malaria for national vector borne disease control programme 2006-07. Delhi: National Institute of Malaria Research and National Vector Borne Disease Control Programme; 2007.

(5.) WHO. Insecticide treated mosquito nets: A position statement. Geneva: World Health Organization; 2007.

(6.) WHO. WHO recommended long-lasting insecticidal mosquito nets. Available at: http://www.who.int/whopes/Long_lasting_insecticidal nets ok2.pdf accessed on September 17, 2008.

(7.) WHO. Report of 11th WHOPES Working Group; 2008. Available at: http://whqlibdoc, who. int/hq/2008/ WHO_HTM_NTD_WHOPES 2008. l_eng.pdf accessed on September 17, 2008.

(8.) Tami A, Mubyazi G, Talbert A, Mshinda H, Duchon S, Lengeler C. Evaluation of Olyset[TM] insecticide-treated nets distributed seven years previously in Tanzania. Malar J 2004; 3 : 19.

(9.) Kilian A, Byamukama W, Pigeon O, Atieli F, Duchon S, Phan C. Long-term field performance of a polyester-based long-lasting insecticidal mosquito net in rural Uganda. Malar J 2008; 7 : 49.

(10.) WHO. Guidelines for laboratory and field testing of longlasting insecticidal mosquito nets; 2005. Available at: http:// whqlibdoc.who.int/hq/2005/WHO_CDS WHOPES_ GCDPP2005.11.pdf accessed on September 17, 2008.

(11.) Sharma SK, Upadhyay AK, Haque MA, Padhan K, Tyagi PK, Ansari MA, et al. Wash resistance and bioefficacy of Olyset net- A long-lasting insecticide-treated mosquito net against malaria vectors and nontarget household pests. J Med Entomol 2006; 43 : 884-8.

(12.) Gunasekaran K, Vaidyanathan K. Wash resistance of PermaNets in comparison to hand-treated nets. Acta Trop 2008; 105 : 154-7.

(13.) WHO. Long-lasting insecticidal nets for malaria prevention. A manual for malaria programme managers. Trial edition. Geneva: World Health Organization; 2007. Available at: http:/ /www.who.int/malaria/docs/itn/LL1Nmanual.pdf, accessed on September 17, 2008.

A.P. Dash * & R.S. Yadav **

National Institute of Malaria Research

22 Sham Nath Marg

Delhi 110 054, India

For correspondence: * apdash2@rediffmail.com; ** rajpalyadav@gmail.com
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Title Annotation:Commentary
Author:Dash, A.P.; Yadav, R.S.
Publication:Indian Journal of Medical Research
Article Type:Report
Geographic Code:9INDI
Date:Sep 1, 2008
Words:1448
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