Hi Everyone. Interesting paper published recently “Madumla, Edith P., et al. ““In starvation, a bone can also be meat”: a mixed methods evaluation of factors associated with discarding of long-lasting insecticidal nets in Bagamoyo, Tanzania.” Malaria Journal 21.1 (2022): 1-19.” on duration of use and methods of discarding old nets in Tanzania.  They mention that between the years 2000 and 2019 more than 1,8 billion LLIN’s were distributed. Insectidal duration typically around 3 years, but most nets discarded after about 2 years. Evidence from Tanzania suggests that decision to discard nets is mostly related to physical integrity of nets. Most common methods for getting rid of the nets is by burning or burial.

If you ever had doubts about the role of vector control in combatting malaria, think on these words taken from the highly-cited 2015 publication by Bahtt et al “In total, we estimated that malaria control interventions have averted 663 (542–753) million clinical cases since 2000, of which 68 (62-73)%, 22 (17-28)% and 10 (5-14)% were contributed by ITNs, ACTs, and IRS, respectively“. 68% of clinical cases averted between 2000 and 2015 can be attributed to the use of bednets, and then another 10% through Indoor Residual Spraying. That kind of sums it up. In fact, ever since it was discovered in 1898 that malaria was transmitted by Anopheles mosquitoes, malaria control has consistently and overwhelmingly relied on vector control. So do not let anyone tell you that entomologists are no longer relevant and important in control of vector-borne diseases, and that goes for arboviruses as well.

Here is the reference to the paper published by Bhatt et al in Nature in 2015 : Bhatt, Samir, D. J. Weiss, E. Cameron, D. Bisanzio, B. Mappin, U. Dalrymple, K. E. Battle et al. “The effect of malaria control on Plasmodium falciparum in Africa between 2000 and 2015.” Nature 526, no. 7572 (2015): 207-211.

Yet more confirmation that globally there is a need for capacity strengthening in national vector control agencies in the ability of countries to effectively respond to mosquito-borne diseases. Here is a hot-off-the-press publication regarding the WHO Eastern Mediterranean Region:

How far are we? National preparedness and response capacities for emerging infectious disease outbreaks in the WHO Eastern Mediterranean Region Lubna Al Ariqi ,1 Evans Buliva,1 Abrar Ahmad Chughtai ,2 Amal Barakat,1 Chiori Kodama ,1 Wasiq Khan,1 Muhammad Tayyab,1 Sherein El Nossery,1 Amir Aman,1 Tamer El-Maghraby, 1 Amgad Elkholy,1 Abdinasir Abubakar1

They say: ⇒ Ministries of Health in 22 countries of the WHO Eastern Mediterranean Region adopted the Strategic Framework for Prevention and Control of Emerging and Epidemic Prone Infectious Diseases in the Region for 2020–2024. To characterise the baseline national capacities pertaining to regional high-threat pathogens for monitoring implementation progress of this framework, an assessment was merited. ⇒ Countries in the Region reported varying levels of capacities, with relatively highest capacities in early detection and investigation of outbreaks and lowest capacities in prevention and preparedness. Countries experiencing humanitarian emergencies have reported relatively lower capacities across all areas. ⇒ The findings suggest that the 22 countries in the Region need to accelerate building their capacities to achieve the framework’s 2024 endorsed target goals.

You can access the article at https://gh.bmj.com/content/bmjgh/7/Suppl_4/e009826.full.pdf.

Thanks for your information, Dr. Leo and Wulan!

There is an interesting, easy-to-read article on the new Interceptor G2 New Generation bednet, which combines the usual synthetic pyrethroid with a new compound, Chlorfenapyr, which targets the insects mitochondrial energy centres. Trials in Africa have found very encouraging results for Interceptor G2, and it is hoped that WHO will officially endorse and recommend IG2 in 2023. Article written by Helen Jamet at Gates Foundation. Read the full story at https://www.gatesfoundation.org/ideas/articles/ig2-nets-malaria-eradication-financed-by-the-global-fund?utm_source=to&utm_medium=em&utm_campaign=wc&utm_term=lgc

Wow. Fascinating article that explains how mosquitoes prefer to rest on vertical surfaces, but are only able to “hang on” to such vertical surfaces if they are above a certain threshold of roughness, otherwise they cannot hold on. So if you can spray a “smoothener” onto the surface the mosquitoes cannot land. Read here:

Recla L, Rheault M, Golovin K. Complete Inhibition of Vertical Mosquito Landing through Topographical Surface Design. ACS Applied Materials & Interfaces. 2022 Aug 12.

SHORT VIDEO ON MODE OF ACTION OF CHLORFENAPYR…PYRROLE CLASS OF INSECTICIDES

I found this short video (2 minutes 45 seconds) very interesting and well-produced. You can find it at Chlorfenapyr – a new approach (basf.com). It explains how the chemical works in simple language, not to disrupt neurotransmission, but mitochondrial energy disruption.

Physical durability: are bed nets getting any stronger? Malaria Journal 13 Jan 2024

This abstract is taken from the journal article: Wheldrake A, Guillemois E, Arouni H, Chetty V, Zappa E, Russell SJ. Physical durability: are bed nets getting any stronger?. Malaria Journal. 2024 Jan 13;23(1):19.

For at least a decade, concerns have been raised about the physical durability of insecticide-treated nets (ITNs) and their ability to remain in good condition for at least three years. To discover if the resistance to damage (RD) of ITNs has improved or not, the RD scores of ITNs sampled in 2013 and 2020 were compared. The RD scores and disaggregated textile performance data for nine ITNs recommended by the WHO pesticide evaluation scheme (WHOPES) measured in 2013 were compared with WHO-prequalified ITNs sampled in 2020. This included assessment of newer ITNs not available in 2013, to determine the extent to which product development has led to performance improvements across all available ITNs in the intervening years. The resistance to damage of ITNs has not generally improved from 2013 to 2020, and in some cases performance is worse. The average RD score of comparable ITNs brands decreased from 40 in 2013 to 36 in 2020. Of the nets available in 2020, only two of the twenty-four ITN products tested achieved an RD score of > 50, while six ITNs had very low RD scores of < 30, highlighting a serious inherent, and literal weakness in many WHO-prequalified ITNs. Conclusions – The long-term physical durability of ITN products cannot be expected to improve while their resistance to damage remains so low, and major upgrades to the performance standards of textile materials used to make ITNs, as well as incentives to develop stronger ones are urgently required.

Very important findings: Reducing Malaria Transmission through Reactive Indoor Residual Spraying: A Systematic Review AJTMH 20 Dec 2023

This abstract from the journal: Gimnig JE, Steinhardt LC, Awolola TS, Impoinvil D, Zohdy S, Lindblade KA. Reducing Malaria Transmission through Reactive Indoor Residual Spraying: A Systematic Review. The American Journal of Tropical Medicine and Hygiene. 2023 Dec 20:tpmd220745-.

In the final stages of malaria elimination, interventions to reduce malaria transmission are often centered around a confirmed case of malaria, as cases tend to cluster together at very low levels of transmission. The WHO commissioned a systematic review of the literature and synthesis of evidence for reactive indoor residual spraying (IRS) to develop official recommendations for countries. This review found that reactive IRS reduces malaria prevalence, probably reduces the incidence of clinical malaria, and probably results in little to no difference in adverse events compared with no reactive IRS. This review suggests that in comparison to proactive, focal IRS, reactive IRS probably results in little to no difference in the incidence of clinical malaria, suggesting that it is as equally effective as proactive, focal IRS. The evidence indicates that reactive IRS may be a cost-effective tool for the prevention of malaria in elimination settings.

Field evaluation of a volatile pyrethroid spatial repellent and etofenprox-treated clothing for outdoor protection against forest malaria vectors in Cambodia BioRxiv preprint

This article is a preprint and has not been certified by peer review, but the findings are really interesting and bode well. Well worth reading! The abstract below is taken from the pre-review journal article in Vajda ÉA, Ross A, Doum D, Fairbanks E, Chitnis NA, Hii J, Moore SJ, Richardson J, Macdonald M, Sovannaroth S, Kimheng P. Field evaluation of a volatile pyrethroid spatial repellent and etofenprox-treated clothing for outdoor protection against forest malaria vectors in Cambodia. bioRxiv. 2024:2024-01.

In this field study the authors evaluated the outdoor application of one passive, transfluthrin-based spatial repellents (VPSR), four etofenprox treated clothing (ITC) paired with a picaridin topical repellent, and a combination of spatial repellents and ITC against wild Anopheles landing in Cambodia. Mathematical modeling was also used to predict the reduction of vectorial capacity of these interventions. A 7×7 Latin-square (6 interventions and one control) was conducted over 49 collection nights in seven temporary, open structures in a forest in Mondulkiri Province, Cambodia. Pairs of participants conducted human landing catches (HLCs). All six interventions reduced Anopheles landing substantially; protective efficacies ranged between 61% (95% confidence interval (CI): 48 – 71%) (etofenprox-ITC, washed) and 95% (95% CI: 93 – 96%) (combined VPSR and unwashed etofenprox-ITC). Finally, the modelling assessment demonstrates significant reductions in vectoral capacity, with the highest impact observed for the combined ITC and VPSR as well as the VPSR used alone, although effectiveness decreases with intervention aging, and variability exists in the magnitude of predicted reductions due to differences in experimental conditions. These transfluthrin-based VPSR and etofenprox ITC interventions have the potential to reduce outdoor and daytime Anopheles biting by providing substantial protection against Anopheles landing.

Optimizing malaria vector control in the Greater Mekong Subregion: a systematic review and mathematical modelling study to identify desirable intervention characteristics

Very interesting article that appeared recently: Wang Y, Chitnis N, Fairbanks EL. Optimizing malaria vector control in the Greater Mekong Subregion: a systematic review and mathematical modelling study to identify desirable intervention characteristics. Parasites & Vectors. 2024 Dec;17(1):1-6.

Here is the Abstract below:

Background

In the Greater Mekong Subregion (GMS), new vector-control tools are needed to target mosquitoes that bite outside during the daytime and night-time to advance malaria elimination.

Methods

We conducted systematic literature searches to generate a bionomic dataset of the main malaria vectors in the GMS, including human blood index (HBI), parity proportion, sac proportion (proportion with uncontracted ovary sacs, indicating the amount of time until they returned to host seeking after oviposition) and the resting period duration. We then performed global sensitivity analyses to assess the influence of bionomics and intervention characteristics on vectorial capacity.

Results

Our review showed that Anopheles minimus, An. sinensis, An. maculatus and An. sundaicus display opportunistic blood-feeding behaviour, while An. dirus is more anthropophilic. Multivariate regression analysis indicated that environmental, climatic and sampling factors influence the proportion of parous mosquitoes, and resting duration varies seasonally. Sensitivity analysis highlighted HBI and parity proportion as the most influential bionomic parameters, followed by resting duration. Killing before feeding is always a desirable characteristic across all settings in the GMS. Disarming is also a desirable characteristic in settings with a low HBI. Repelling is only an effective strategy in settings with a low HBI and low parity proportion. Killing after feeding is only a desirable characteristic if the HBI and parity proportions in the setting are high.

Conclusions

Although in general adopting tools that kill before feeding would have the largest community-level effect on reducing outdoor transmission, other modes of action can be effective. Current tools in development which target outdoor biting mosquitoes should be implemented in different settings dependent on their characteristics.