Publications by authors named "S R Irish"

82 Publications

The potential impact of Anopheles stephensi establishment on the transmission of Plasmodium falciparum in Ethiopia and prospective control measures.

BMC Med 2022 Apr 20;20(1):135. Epub 2022 Apr 20.

MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK.

Background: Sub-Saharan Africa has seen substantial reductions in cases and deaths due to malaria over the past two decades. While this reduction is primarily due to an increasing expansion of interventions, urbanisation has played its part as urban areas typically experience substantially less malaria transmission than rural areas. However, this may be partially lost with the invasion and establishment of Anopheles stephensi. A. stephensi, the primary urban malaria vector in Asia, was first detected in Africa in 2012 in Djibouti and was subsequently identified in Ethiopia in 2016, and later in Sudan and Somalia. In Djibouti, malaria cases have increased 30-fold from 2012 to 2019 though the impact in the wider region remains unclear.

Methods: Here, we have adapted an existing model of mechanistic malaria transmission to estimate the increase in vector density required to explain the trends in malaria cases seen in Djibouti. To account for the observed plasticity in An. stephensi behaviour, and the unknowns of how it will establish in a novel environment, we sample behavioural parameters in order to account for a wide range of uncertainty. This quantification is then applied to Ethiopia, considering temperature-dependent extrinsic incubation periods, pre-existing vector-control interventions and Plasmodium falciparum prevalence in order to assess the potential impact of An. stephensi establishment on P. falciparum transmission. Following this, we estimate the potential impact of scaling up ITN (insecticide-treated nets)/IRS (indoor residual spraying) and implementing piperonyl butoxide (PBO) ITNs and larval source management, as well as their economic costs.

Results: We estimate that annual P. falciparum malaria cases could increase by 50% (95% CI 14-90) if no additional interventions are implemented. The implementation of sufficient control measures to reduce malaria transmission to pre-stephensi levels will cost hundreds of millions of USD.

Conclusions: Substantial heterogeneity across the country is predicted and large increases in vector control interventions could be needed to prevent a major public health emergency.
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http://dx.doi.org/10.1186/s12916-022-02324-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9020030PMC
April 2022

Evaluation of an accelerometer-based monitor for detecting bed net use and human entry/exit using a machine learning algorithm.

Malar J 2022 Mar 12;21(1):85. Epub 2022 Mar 12.

Opportunity Solutions International, San Francisco, CA, 94118, USA.

Background: Distribution of long-lasting insecticidal bed nets (LLINs) is one of the main control strategies for malaria. Improving malaria prevention programmes requires understanding usage patterns in households receiving LLINs, but there are limits to what standard cross-sectional surveys of self-reported LLIN use can provide. This study was designed to assess the performance of an accelerometer-based approach for measuring a range of LLIN use behaviours as a proof of concept for more granular LLIN-use monitoring over longer time periods.

Methods: This study was carried out under controlled conditions from May to July 2018 in Liverpool, UK. A single accelerometer was affixed to the side panel of an LLIN and participants carried out five LLIN use behaviours: (1) unfurling a net; (2) entering an unfurled net; (3) lying still as if sleeping; (4) exiting from under a net; and, (5) folding up a net. The randomForest package in R, a supervised non-linear classification algorithm, was used to train models on 20-s epochs of tagged accelerometer data. Models were compared in a validation dataset using overall accuracy, sensitivity and specificity, receiver operating curves and the area under the curve (AUC).

Results: The five-category model had overall accuracy of 82.9% in the validation dataset, a sensitivity of 0.681 for entering a net, 0.632 for exiting, 0.733 for net down, and 0.800 for net up. A simplified four-category model, combining entering/exiting a net into one category had accuracy of 94.8%, and increased sensitivity for net down (0.756) and net up (0.829). A further simplified three-category model, identifying sleeping, net up, and a combined net down/enter/exit category had accuracy of 96.2% (483/502), with an AUC of 0.997 for net down and 0.987 for net up. Models for detecting entering/exiting by adults were significantly more accurate than for children (87.8% vs 70.0%; pā€‰<ā€‰0.001) and had a higher AUC (pā€‰=ā€‰0.03).

Conclusions: Understanding how LLINs are used is crucial for planning malaria prevention programmes. Accelerometer-based systems provide a promising new methodology for studying LLIN use. Further work exploring accelerometer placement, frequency of measurements and other machine learning approaches could make these methods even more accurate in the future.
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http://dx.doi.org/10.1186/s12936-022-04102-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8917707PMC
March 2022

Detection and population genetic analysis of kdr L1014F variant in eastern Ethiopian Anopheles stephensi.

Infect Genet Evol 2022 04 2;99:105235. Epub 2022 Feb 2.

Department of Biology, Baylor University, Waco, TX, USA. Electronic address:

Anopheles stephensi is a malaria vector that has been recently introduced into East Africa, where it threatens to increase malaria disease burden. The use of insecticides, especially pyrethroids, is still one of the primary malaria vector control strategies worldwide. The knockdown resistance (kdr) mutation in the IIS6 transmembrane segment of the voltage-gated sodium channel (vgsc) is one of the main molecular mechanisms of pyrethroid resistance in Anopheles. Extensive pyrethroid resistance in An. stephensi has been previously reported in Ethiopia. Thus, it is important to determine whether or not the kdr mutation is present in An. stephensi populations in Ethiopia to inform vector control strategies. In the present study, the kdr locus was analyzed in An. stephensi collected from ten urban sites (Awash Sebat Kilo, Bati, Dire Dawa, Degehabur, Erer Gota, Godey, Gewane, Jigjiga, Semera, and Kebridehar) situated in Somali, Afar, and Amhara regions, and Dire Dawa Administrative City, to evaluate the frequency and evolution of kdr mutations and the association of the mutation with permethrin resistance phenotypes. Permethrin is one of the pyrethroid insecticides used for vector control in eastern Ethiopia. DNA extractions were performed on adult mosquitoes from CDC light trap collections and those raised from larval and pupal collections. PCR and targeted sequencing were used to analyze the IIS6 transmembrane segment of the vgsc gene. Of 159 An. stephensi specimens analyzed from the population survey, nine (5.7%) carried the kdr mutation (L1014F). An. stephensi with kdr mutations were only observed from Bati, Degehabur, Dire Dawa, Gewane, and Semera. We further selected randomly twenty resistant and twenty susceptible An. stephensi mosquitoes from Dire Dawa post-exposure to permethrin and investigated the role of kdr in pyrethroid resistance by comparing the vgsc gene in the two populations. We found no kdr mutations in the permethrin-resistant mosquitoes. Population genetic analysis of the sequences, including neighboring introns, revealed limited evidence of non-neutral evolution (e.g., selection) at this locus. The low kdr mutation frequency detected and the lack of kdr mutation in the permethrin-resistant mosquitoes suggest the existence of other molecular mechanisms of pyrethroid resistance in eastern Ethiopian An. stephensi.
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http://dx.doi.org/10.1016/j.meegid.2022.105235DOI Listing
April 2022

Developing Consensus Standard Operating Procedures (SOPs) to Evaluate New Types of Insecticide-Treated Nets.

Insects 2021 Dec 21;13(1). Epub 2021 Dec 21.

Department of Vector Biology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UK.

In response to growing concerns over the sustained effectiveness of pyrethroid-only based control tools, new products are being developed and evaluated. Some examples of these are dual-active ingredient (AI) insecticide-treated nets (ITNs) which contain secondary insecticides, or synergist ITNs which contain insecticide synergist, both in combination with a pyrethroid. These net types are often termed 'next-generation' insecticide-treated nets. Several of these new types of ITNs are being evaluated in large-scale randomized control trials (RCTs) and pilot deployment schemes at a country level. However, no methods for measuring the biological durability of the AIs or synergists on these products are currently recommended. In this publication, we describe a pipeline used to collate and interrogate several different methods to produce a singular 'consensus standard operating procedure (SOP)', for monitoring the biological durability of three new types of ITNs: pyrethroid + piperonyl butoxide (PBO), pyrethroid + pyriproxyfen (PPF), and pyrethroid + chlorfenapyr (CFP). This process, convened under the auspices of the Innovation to Impact programme, sought to align methodologies used for conducting durability monitoring activities of next-generation ITNs.
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http://dx.doi.org/10.3390/insects13010007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8778287PMC
December 2021

The effect of long-lasting insecticidal nets (LLINs) physical integrity on utilization.

Malar J 2021 Dec 18;20(1):468. Epub 2021 Dec 18.

Tulane University School of Public Health and Tropical Medicine, New Orleans, LA, USA.

Background: In Ethiopia, despite improvements in coverage and access, utilization of long-lasting insecticidal nets (LLINs) remains a challenge. Different household-level factors have been identified as associated with LLIN use. However, the contribution of LLIN physical integrity to their utilization is not well investigated and documented. This study aimed to assess the association between the physical integrity of LLINs and their use.

Methods: This study employed a nested case-control design using secondary data from the Ethiopian LLIN durability monitoring study conducted from May 2015 to June 2018. LLINs not used the night before the survey were identified as cases, while those used the previous night were categorized as controls. The physical integrity of LLINs was classified as no holes, good, acceptable, and torn using the proportionate hole index (pHI). A Generalized Estimating Equation (GEE) model was used to assess and quantify the association between LLIN physical integrity and use. The model specifications included binomial probabilistic distribution, logit link, exchangeable correlation matrix structure, and robust standard errors. The factors included in the model were selected first by fitting binary regression, and then by including all factors that showed statistical significance at P-value less than 0.25 and conceptually relevant variables into the multivariate regression model.

Results: A total of 5277 observations fulfilled the inclusion criteria. Out of these 1767 observations were cases while the remaining 3510 were controls. LLINs that were in torn physical condition had higher odds (AOR [95% CI] = 1.76 [1.41, 2.19]) of not being used compared to LLINs with no holes. Other factors that showed significant association included the age of the LLIN, sleeping place type, washing status of LLINs, perceptions towards net care and repair, LLIN to people ratio, economic status, and study site.

Conclusion And Recommendation: LLINs that have some level of physical damage have a relatively higher likelihood of not being used. Community members need to be educated about proper care and prevention of LLIN damage to delay the development of holes as long as possible and use available LLINs regularly.
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http://dx.doi.org/10.1186/s12936-021-03976-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8684122PMC
December 2021
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