WHO moves against malaria with two fortified nets

To contain mosquitoes, the World Health Organisation (WHO) has introduced two insecticide-treated nets (ITNs).

In a statement, yesterday, the global agency observed that since 2005, over two billion ITNs have been distributed globally to prevent malaria. All of these nets were treated with only one insecticide – pyrethroids.

However, as mosquitoes become resistant to insecticide, nets treated with other active ingredients were needed to control malaria.

In 2017, WHO began recommending a new type of ITN that combines pyrethroids with piperonyl-butoxide (PBO), a chemical, which enhances potency of pyrethroids against resistant mosquitoes.

Leader of Vector Control and Insecticide Resistance Unit within the WHO Global Malaria Programme, Dr. Jan Kolaczinski, noted: “These new types of nets were designed to have a greater impact against pyrethroid-resistant mosquitoes. By including two active ingredients in an ITN, the likelihood of mosquitoes being resistant to both is greatly reduced.”

The consolidated WHO guidelines bring together the organisation’s up-to-date recommendations for malaria in a single web-based document.

Recommendations are reviewed and, where appropriate, updated using WHO’s transparent and rigorous guideline development process. The guidelines are also available in the user-friendly MAGICapp platform, which always displays the updated recommendations and date of most recent revision.

WHO is issuing a strong recommendation for deployment of pyrethroid-chlorfenapyr ITNs versus pyrethroid-only nets to prevent malaria in adults and children in areas, where mosquitoes have become resistant to pyrethroids.

The suggestion considers that, compared to pyrethroid-only nets or pyrethroid-PBO nets, pyrethroid-chlorfenapyr ITNs should have an increased killing effect against pyrethroid-resistant malaria vectors and, thus, a greater impact against malaria.

WHO is releasing a conditional recommendation for deployment of pyrethroid-chlorfenapyr ITNs instead of pyrethroid-PBO nets to prevent malaria in adults and children in areas with pyrethroid resistance.

The conditionality is based on judgment of the WHO Guidelines Review Group (GDG) that the balance of desirable and undesirable effects probably favours pyrethroid-chlorfenapyr nets over pyrethroid-PBO nets. The recommendation is based on evidence drawn from only one trial in Africa.

The body is also out with a conditional recommendation for deployment of pyrethroid-pyriproxyfen nets instead of pyrethroid-only nets to prevent malaria in adults and children in areas with pyrethroid resistance.

The move is based on GDG’s concerns around the poor cost-effectiveness of pyrethroid-pyriproxyfen nets compared to pyrethroid-only nets; extra resources currently required to purchase these ITNs, it said, may have a negative impact on coverage and equity.

The organisation went on: “In 2007, WHO adopted GRADE (Grading of Recommendations Assessment, Development and Evaluation) as the method for assessing quality of a body of evidence and for determining the direction and strength of the resulting recommendations. GRADE categorises the quality of evidence as high, moderate, low or very low. GRADE assessments are determined through consideration of several factors, including risk of bias, inconsistency, indirectness, imprecision and publication bias. All of the recommendations published today are based on a moderate certainty of evidence.”

Together with the new recommendations, WHO is publishing new guidance to support national malaria programmes in decisions, on which nets to prioritise in resource-limited settings.

This guidance focuses, as a first step, on ensuring coverage of ITNs for vulnerable groups – particularly pregnant women and children under the age of five – and then on planning for high-volume net distribution campaigns. While the guidance is based on best practices generated in Africa in recent years, it can be used as a component of prioritisation processes by all countries deploying ITNs.

Over the last two decades, ITNs have contributed significantly to progress seen in reducing malaria cases worldwide.

A 2015 modelling analysis published in Nature suggested that ITNs drove most of the declines in malaria witnessed from 2005–2015, especially in moderate-to-high transmission areas. However, progress since 2015 has slowed.

According to WHO’s latest World malaria report, the emergence and wide geographic spread of pyrethroid resistance among malaria-transmitting mosquitoes is the most recognised threat to effectiveness of ITNs.

Other threats to this key prevention tool include insufficient coverage and access; challenges relating to physical and chemical durability of nets and changing behaviour of mosquitoes, which appears to be biting early before people go to bed, and resting outdoors, thereby evading exposure to insecticides.