Background on Long-Lasting Insecticidal Nets (LLINs) and Malaria

Long-Lasting Insecticidal Nets (LLINs) have emerged as a cornerstone in the fight against malaria, a disease that remains a significant public health challenge in many parts of the world, particularly in sub-Saharan Africa and South Asia. The World Health Organization (WHO) has emphasized the importance of LLINs as effective tools for malaria prevention. These nets not only provide a physical barrier against malaria-transmitting Anopheles mosquitoes but also incorporate insecticides that remain effective for several years post-manufacture. Originally, insecticide-treated nets needed re-impregnation every six to twelve months, but LLINs, introduced in the early 2000s, are designed to retain their insecticidal properties for up to five years (Vink et al., 2025).

Despite their proven efficacy, the durability and performance of LLINs can be affected by various factors such as environmental conditions, usage patterns, and maintenance practices. Understanding these factors is critical for ensuring that LLINs continue to provide adequate protection against malaria transmission over time.

Importance of LLIN Survivorship and Usage in Afghanistan

In Afghanistan, malaria remains endemic in various regions, with significant annual case numbers reported. An estimated 8.2 million people are at risk of malaria, predominantly due to Plasmodium vivax and Plasmodium falciparum infections. The Afghan national malaria control strategy relies heavily on LLIN distribution among at-risk populations. Between 2007 and 2014, over 9 million LLINs were distributed across malaria-endemic provinces. The survivorship and continued usage of these nets are crucial to maintaining a low malaria incidence rate in the country.

A recent study by Vink et al. (2025) found that 87.8% of LLINs distributed were still present in households three years after distribution, demonstrating high survivorship. Additionally, 96.3% of these nets were reported to be used regularly, indicating effective utilization among households. Such data are vital for the planning of replacement and replenishment campaigns, as continuous usage of LLINs significantly contributes to malaria control efforts.

Physical Integrity and Insecticidal Activity of LLINs

The physical integrity of LLINs is a critical factor in their effectiveness. The study conducted in Afghanistan reported that 97.0% of the LLINs were in a serviceable condition, indicating minimal damage. The proportionate Hole Index (pHI), which measures the extent of damage, showed that the majority of nets were in good condition (pHI 0–64), while only a small percentage were considered too torn (pHI > 642). This suggests that the nets retained their structural integrity, which is essential for their functionality.

However, despite good physical integrity, the insecticidal activity of these LLINs showed a decline over the three-year period. Only 28% of the tested nets met the WHO criteria for mosquito mortality (≥ 80%), with a median deltamethrin concentration of 0.12 g/kg netting material—just 6.7% of the original concentration. This decline is concerning as it indicates that while the nets may still provide a physical barrier, their chemical efficacy in killing mosquitoes has significantly diminished (Vink et al., 2025).

Impact of Washing Practices on LLIN Efficacy

Washing practices have a substantial impact on the efficacy of LLINs. The study highlighted that washing LLINs was associated with a significant reduction in mosquito mortality rates. LLINs that had not been washed showed much higher insecticidal activity compared to those that had been laundered. Specifically, 42.9% of the unwashed nets achieved a mortality rate of ≥ 80%, while only 21.6% of washed nets met this criterion. This finding underscores the importance of educating LLIN users about proper care and maintenance to extend the life and effectiveness of these nets.

Table 1 summarizes the correlation between washing practices and LLIN efficacy:

Washing Method	Mosquito Mortality ≥ 80% (%)	Deltamethrin Concentration (g/kg)
Not Washed	42.9	0.25 (IQR 0.12–0.87)
Washed	21.6	0.10 (IQR −0.03 to 0.23)

Recommendations for LLIN Maintenance and Future Research

To enhance the durability and efficacy of LLINs, several recommendations can be made based on the findings of the study:

Education on Proper Usage: Health authorities should implement educational programs to inform communities about the importance of maintaining LLINs, including proper washing and drying practices. This can help minimize damage and retain insecticidal properties.
Regular Monitoring: Conducting regular assessments of LLIN survivorship and performance in the field is crucial. This can help identify any decline in efficacy early and facilitate timely replacement or replenishment of LLINs.
Further Research: Additional studies are needed to explore the factors influencing LLIN durability in various environmental conditions, particularly in seasonal malaria transmission areas. Understanding the impact of different washing methods and materials on insecticidal content can guide manufacturers in producing more resilient nets.
Policy Development: Policymakers should consider integrating findings from LLIN durability studies into national malaria control strategies to ensure that resources are effectively allocated to maintain high coverage and efficacy of malaria prevention tools.

FAQ

What are Long-Lasting Insecticidal Nets?
LLINs are bed nets treated with insecticides that remain effective for several years, providing protection against malaria-carrying mosquitoes.

How effective are LLINs in preventing malaria?
LLINs have been shown to significantly reduce malaria incidence by providing both a physical barrier and a chemical kill effect on mosquitoes.

How can I maintain my LLIN?
To maintain your LLIN, avoid washing it frequently, especially with detergents. If washing is necessary, use mild soap and dry it in the shade to preserve its insecticidal properties.

What should I do if my LLIN is damaged?
If your LLIN is damaged, report it to your local health authorities for a replacement. Do not use heavily torn nets as they may not be effective.

How often should LLINs be replaced?
LLINs should be replaced every three to five years, depending on their condition and usage patterns.

References

Vink, M., Ahmad, M., Sabawoon, M. F., Nahzat, M. S., Siddiqi, A. M., Naseem, M., Alizoi, N., Najeebullah, S., Schallig, H. D., Bradley, J., Moore, S., & Schim van der Loeff, M. F. (2025). Do long-lasting insecticidal nets retain their efficacy after three years of usage in Afghanistan? Findings from a study on survivorship, physical integrity, insecticidal activity and wash resistance. Malaria Journal, 24, 1384. https://doi.org/10.1186/s12936-025-05346-1
WHO. (2013). Guidelines for laboratory and field testing of long-lasting insecticidal nets (WHO/HTM/NTD/WHOPES/2013.3). Geneva: World Health Organization.
WHO. (2023). World Malaria Report 2023. Geneva: World Health Organization.
Gichuki, P. M., Kamau, L., Njagi, K., Karoki, S., Muigai, N., & Matoke-Muhia, D. (2021). Bioefficacy and durability of Olyset® Plus, a permethrin and piperonyl butoxide-treated insecticidal net in a 3-year long trial in Kenya. Infectious Diseases of Poverty, 10(1), 135. https://doi.org/10.1186/s40249-021-00916-2
Sahu, S. S., Keshaowar, A. V., Thankachy, S., Panigrahi, D. K., Acharya, P., & Balakrishnan, V. (2020). Evaluation of bio-efficacy and durability of long-lasting insecticidal nets distributed by malaria elimination programme in Eastern India. Malaria Journal, 19, 186. https://doi.org/10.1186/s12936-020-03260-2