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Retreatment of Insecticide-treated Nets

Overview:

The use of insecticide-treated nets (ITNs) has been widely adopted as an important method for malaria control and is effective at reducing causes of malaria mortality and morbidity by between 17 and 43% in children under five years old, as well as giving protection to pregnant women. The most important vectors of malaria in sub-Saharan Africa all bite predominantly indoors between sunset and sunrise so that sleeping under a treated net during this period can greatly reduce exposure to mosquitoes and provide good protection against malaria. The efficacy of ITNs for preventing malaria is well established and they are known to provide substantial protection to both individuals and communities that use them. When a whole community is provided with treated nets, so many mosquitoes of anthropophilic species are killed by contact with the nets that the density and/or infection rate of the vector population is reduced. In order to gain this "mass" or community effect, in addition to widespread personal protection, and thus to achieve the full potential of the treated net method, a high percentage coverage of the community is needed.

Treated nets, however, have a limited life span as the insecticide is lost during washing and in exposure to bright sunlight. Retreatment of nets is required every 6 months to 1 year; less if the net has been exposed to sunlight. The regular use of nets can fall, as users may feel that a recurrence in malaria infection rates is due more to seasonality of transmission rather than lower efficacy of the nets and their trust in the nets' use may drop. However retreating nets requires a number of factors: provision of insecticide, sufficient personnel trained in treating, delivery of treatment and sensitisation of the community to why this is necessary. Retreatment can also be variable unless the operator dilutes the insecticide correctly. Until Long Lasting Insecticidal Nets (LLINs; see entry) predominate, retreatment of ITNs is important.

Effective monitoring and evaluation of the use of nets in a community take into account the proportion of households with ITNs (coverage), the proportion of nets used each night (adherence) and the proportion of nets still treated with insecticide (treatment).

Key points:

  • The use of insecticide-treated mosquito nets in preventing malaria is well accepted.
  • Many insecticide formulations only last a finite time - 6 to 12 months.
  • Re-treatment of nets requires education and sensitisation to achieve good coverage.
  • Long lasting insecticidal nets obviate the need for retreatment, thereby making them more cost effective and more sustainable, but retreatment will  be needed until coverage with LLINs is more widespread.

 

Case Study:

The Malaria Consortium works with Uganda Ministry of Health on a retreatment programme for ITNs.

Aims:

  • Retreat 50% of the existing nets in the 20 high net coverage districts (where more than 10% households already have nets).
  • Create public awareness on the importance of treating mosquito nets (increases in transmission may be due to reduced insecticidal capacity of nets, rather than seasonality of transmission).
  • Build capacity and alliances for the implementation of net retreatment campaigns.
  • Solicit participation of partners in the promotion of net retreatment campaigns

The method:

The innovative plastic bag method was chosen. This involved the net being treated in a plastic bag by a trained dipper at a village dipping point and being taken home by the net owner to dry. This pioneering method was easy to carry out, allowed high volumes of nets to be treated, ensured privacy for the net owner, and guaranteed the insecticide was only used for the net.

As of July 2004, the first round of this programme was evaluated. There was excellent coverage of re-treatment (74% of nets, where 50% was initially the target), which incorporated the logistics of training personnel, educating local people, delivering insecticide and treating the nets successfully. Because the programme was designed with local partners and community capacity development, it is expected to have sustainability over the next two to three years until LLINs become widespread, and retreatment is no longer necessary. The cost for retreating was just 75 cents. There was also an increased demand for nets from households during and after the treatment process. [Net Retreatment Project 2] Since this round there have been further successful retreatment campaigns.

 

References:

  1. * Curtis, C.F., Jana-Kara, B. & Maxwell, C.A. (2003) Insecticide Treated Nets: Impact on Vector Populations and Relevance of Initial Intensity of Transmission and Pyrethroid Resistance. Journal of Vector Borne Disease 40:1-8
  2. * Kolaczinski, J. & Hanson, K. (2006). Costing the distribution of insecticide-treated nets: a review of cost and cost-effectiveness studies to provide guidance on standardization of costing methodology. Malaria Journal 5:37.
  3. * Van Nam, N., de Vries, P.J., Toi, L.V. & Nagekerke, N.(2005). Malaria Control in Vietnam, The Binh Thuan Experience.Tropical Medicine and International Health 10(4): 357-365
  4. * Fraser- Hurt, N. & Lyimo, E.O.K. (1996) Insecticide-treated nets and Treatment Services: A trial Using Public and Private Sector Channels in Rural United Republic of Tanzania. Bulletin of the World Health Organization 76(6) 507-615
  5. Hawley, W.A., Te Kuite, F.O., Steketee, R.S. Nahlen, B.L., Terlouw, D.J., Gimnig, J.E., Shi, Y., Vulule, J.M., Alaii, J.A., High Tower, A., Kolczak, M.S., Kariuki, S.K. & Phillips-Howard, P.A.(2003) Implications of the Western Kenya Permenthrin-Treated Bed Nets Study for Policy, Program Implementation and Future Research. The American Society of Tropical Medicine and Hygiene 68 (Suppl 4) 168-173.
  6. * Yates A, N'Guessan R, Kaur H, Akogbéto M, Rowland M (2005) Evaluation of KO-Tab 1-2-3®: a wash-resistant 'dip-it-yourself' insecticide formulation for long-lasting treatment of mosquito nets Malaria Journal 4:52
  7. * Winch, P.J., Makemba,A., Makame, V., Mfaume, M.S., Lynch, M., Prenyi, Z., Minjas, J. & Schiff, C.J. (1997) Social and Cultural Factors Affecting Rates of Regular Retreatment of Mosquito Nets With Insecticide in Bagamoyo District, Tanzania. GTZ, Kabarole District Health service, WHO RBM
  8. * WHO (2002) Instructions for Treatment and Use of Insecticide- Treated Mosquito nets. WHO/CDS/RBM/2002.41
  9. * Root, G. (2005) Designing and Implementing a National Retreatment System in Uganda. Malaria Consortium.
  10. * Killeen, G.F., Kihonda, J., Lyimo, E., Oketch, F.R., Kotas, M.E., Mathenge, E., Schellenberg, J.A., Lengeler, C., Smith, T.A. & Drakeley, C.J. (2006) Quantifying behavioural interactions between humans and mosquitoes: Evaluating the protective efficacy of insecticidal nets against malaria transmission in rural Tanzania. BMC Infectious Diseases 6:161.
  11. * Pacque, M. (2005) Bednets Reduce Malaria. Global Health Technical Briefs.
  12. * RBM Insecticide Treated Mosquito Nets. Roll Back Malaria