Modelling the impact of interventions on imported, introduced and indigenous malaria infections in Zanzibar, Tanzania.
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SUBMITTER: Das AM
PROVIDER: S-EPMC10182017 | biostudies-literature | 2023 May
REPOSITORIES: biostudies-literature
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Modelling the impact of interventions on imported, introduced and indigenous malaria infections in Zanzibar, Tanzania.
Das Aatreyee M AM Hetzel Manuel W MW Yukich Joshua O JO Stuck Logan L Fakih Bakar S BS Al-Mafazy Abdul-Wahid H AH Ali Abdullah A Chitnis Nakul N
Nature communications 20230512 1
Malaria cases can be classified as imported, introduced or indigenous cases. The World Health Organization's definition of malaria elimination requires an area to demonstrate that no new indigenous cases have occurred in the last three years. Here, we present a stochastic metapopulation model of malaria transmission that distinguishes between imported, introduced and indigenous cases, and can be used to test the impact of new interventions in a setting with low transmission and ongoing case impo ...[more]
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Project description:BackgroundZanzibar has made substantial progress in malaria control with vector control, improved diagnosis, and artemisinin-based combination therapy. Parasite prevalence in the population has remained around 1% but imported infections from mainland Tanzania contribute to sustained local transmission. Understanding travel patterns between mainland Tanzania and Zanzibar, and the risk of malaria infection, may help to control malaria importation to Zanzibar.MethodsA rolling cross-sectional survey linked to routine reactive case detection of malaria was carried out in Zanzibar between May 2017 and October 2018. Households of patients diagnosed with malaria at health facilities were surveyed and household members were tested for malaria using rapid diagnostic tests and a sub-sample by quantitative PCR (qPCR). Interviews elicited a detailed travel history of all household members who had travelled within the past two months, including trips within and outside of Zanzibar. We estimated the association of malaria infection with travel destinations in pre-defined malaria endemicity categories, trip duration, and other co-variates using logistic regression.ResultsOf 17,891 survey participants, 1177 (7%) reported a recent trip, of which 769 (65%) visited mainland Tanzania. Among travellers to mainland Tanzania with travel destination details and a qPCR result available, 241/378 (64%) reported traveling to districts with a 'high' malaria endemicity and for 12% the highest endemicity category was 'moderate'. Travelers to the mainland were more likely to be infected with malaria parasites (29%, 108/378) than those traveling within Zanzibar (8%, 16/206) or to other countries (6%, 2/17). Among travellers to mainland Tanzania, those visiting highly endemic districts had a higher odds of being qPCR-positive than those who travelled only to districts where malaria-endemicity was classified as low or very low (adjusted odd ratio = 7.0, 95% confidence interval: 1.9-25.5). Among travellers to the mainland, 110/378 (29%) never or only sometimes used a mosquito net during their travel.ConclusionsStrategies to reduce malaria importation to Zanzibar may benefit from identifying population groups traveling to highly endemic areas in mainland Tanzania. Targeted interventions to prevent and clear infections in these groups may be more feasible than attempting to screen and treat all travellers upon arrival in Zanzibar.
| S-EPMC10464242 | biostudies-literature
Project description:BackgroundImpact evaluations allow countries to assess public health gains achieved through malaria investments. This study uses routine health management information system (HMIS) data from Zanzibar to describe changes in confirmed malaria incidence and impact of case management and vector control interventions during 2000-2015.MethodsHMIS data from 129 (82%) public outpatient facilities were analyzed using interrupted time series models to estimate the impact of artemisinin-based combination therapy (ACT), indoor residual spray, and long-lasting insecticidal nets. Evaluation periods were defined as pre-intervention (January 2000 to August 2003), ACT-only (September 2003 to December 2005) and ACT plus vector control (2006-2015).FindingsAfter accounting for climate, seasonality, diagnostic testing rates, and outpatient attendance, average monthly incidence of confirmed malaria showed no trend over the pre-intervention period 2000-2003 (incidence rate ratio (IRR) 0.998, 95% CI 0.995-1.000). During the ACT-only period (2003-2005), the average monthly malaria incidence rate declined compared to the pre-intervention period, showing an overall declining trend during the ACT-only period (IRR 0.984, 95% CI 0.978-0.990). There was no intercept change at the start of the ACT-only period (IRR 1.081, 95% CI 0.968-1.208), but a drop in intercept was identified at the start of the ACT plus vector control period (IRR 0.683, 95% CI 0.597-0.780). During the ACT plus vector control period (2006-2015), the rate of decline in average monthly malaria incidence slowed compared to the ACT-only period, but the incidence rate continued to show an overall slight declining trend during 2006-2015 (IRR 0.993, 95% CI 0.992-0.994).InterpretationThis study presents a rigorous approach to the use of HMIS data in evaluating the impact of malaria control interventions. Evidence is presented for a rapid decline in malaria incidence during the period of ACT roll out compared to pre-intervention, with a rapid drop in malaria incidence following introduction of vector control and a slower declining incidence trend thereafter.
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Project description:BackgroundTo accelerate progress against malaria in high burden countries, a strategic reorientation of resources at the sub-national level is needed. This paper describes how mathematical modelling was used in mainland Tanzania to support the strategic revision that followed the mid-term review of the 2015-2020 national malaria strategic plan (NMSP) and the epidemiological risk stratification at the council level in 2018.MethodsIntervention mixes, selected by the National Malaria Control Programme, were simulated for each malaria risk strata per council. Intervention mixes included combinations of insecticide-treated bed nets (ITN), indoor residual spraying, larval source management, and intermittent preventive therapies for school children (IPTsc). Effective case management was either based on estimates from the malaria indicator survey in 2016 or set to a hypothetical target of 85%. A previously calibrated mathematical model in OpenMalaria was used to compare intervention impact predictions for prevalence and incidence between 2016 and 2020, or 2022.ResultsFor each malaria risk stratum four to ten intervention mixes were explored. In the low-risk and urban strata, the scenario without a ITN mass campaign in 2019, predicted high increase in prevalence by 2020 and 2022, while in the very-low strata the target prevalence of less than 1% was maintained at low pre-intervention transmission intensity and high case management. In the moderate and high strata, IPTsc in addition to existing vector control was predicted to reduce the incidence by an additional 15% and prevalence by 22%. In the high-risk strata, all interventions together reached a maximum reduction of 76%, with around 70% of that reduction attributable to high case management and ITNs. Overall, the simulated revised NMSP was predicted to achieve a slightly lower prevalence in 2020 compared to the 2015-2020 NMSP (5.3% vs 6.3%).ConclusionModelling supported the choice of intervention per malaria risk strata by providing impact comparisons of various alternative intervention mixes to address specific questions relevant to the country. The use of a council-calibrated model, that reproduces local malaria trends, represents a useful tool for compiling available evidence into a single analytical platform, that complement other evidence, to aid national programmes with decision-making processes.
| S-EPMC8929286 | biostudies-literature
Project description:Hybridization between introduced and indigenous species can lead to loss of unique genetic resources and precipitate extinction. In Tanzania, the Nile tilapia (Oreochromis niloticus) and blue-spotted tilapia (Oreochromis leucostictus) have been widely introduced to non-native habitats for aquaculture and development of capture fisheries. Here, we aimed to quantify interspecific hybridization between these introduced species and the indigenous species Oreochromis esculentus, Oreochromis jipe and Oreochromis korogwe. In the Pangani basin, several hybrids were observed (O. niloticus × O. jipe, O. leucostictus × O. jipe, O. niloticus × O. korogwe), although hybrids were relatively uncommon within samples relative to purebreds. Hybrids between the native O. jipe × O. korogwe were also observed. In the Lake Victoria basin, no evidence of hybrids was found. Analysis of body shape using geometric morphometrics suggested that although purebreds could be discriminated from one another, hybrids could not be readily identified on body and head shape alone. These results provide the first evidence of hybridization between the introduced species and the Critically Endangered O. jipe in Tanzania. Given uncertainty regarding benefits of introduced species over large-bodied indigenous species in aquaculture and capture fisheries, we suggest that future introductions of hybridization-prone species should be carefully evaluated.
| S-EPMC6394572 | biostudies-literature
Project description:Since 2012, the Zanzibar Malaria Elimination Program has been implementing reactive case detection (RACD). Health facility (HF) staff send individual malaria case notifications by using mobile phones, triggering a review of HF records and malaria testing and treatment at the household level by a district malaria surveillance officer. We assessed the completeness and timeliness of this system, from case notification to household-level response. We reviewed two years (2015-2016) of primary register information in 40 randomly selected HFs on Zanzibar's two islands Unguja and Pemba and database records of case notifications from all registered HFs for the period 2013-16. The operational coverage of the system was calculated as proportion of HF-registered cases that were successfully reviewed and followed up at their household. Timeliness was defined as completion of each step within 1 day. Public HFs notified almost all registered cases (91% in Unguja and 87% in Pemba), and 74% of cases registered at public HFs were successfully followed up at their household in Unguja and 79% in Pemba. Timely operational coverage (defined as each step, diagnosis to notification, notification to review, and review to household-level response, completed within 1 day) was achieved for only 25% of registered cases in Unguja and 30% in Pemba. Records and data from private HFs on Unguja indicated poor notification performance in the private sector. Although the RACD system in Zanzibar achieved high operational coverage, timeliness was suboptimal. Patients diagnosed with malaria at private HFs and hospitals appeared to be largely missed by the RACD system.
| S-EPMC7008315 | biostudies-literature
Project description:BackgroundThe state of Goa in western India is world-renowned for its coastline and attracts millions of tourists across the world. Historically, Goa was among the malaria-endemic states in India, with Plasmodium vivax contributing to the majority of the cases. Past malaria outbreaks in Goa have been linked to construction activities, and imported malaria cases threaten malaria elimination efforts in the state.MethodsThe malaria data from the National Centre for Vector Borne Disease Control (NCVBDC) and the Directorate of Health Services, Goa was used to study the spatiotemporal dynamics of Plasmodium falciparum, P. vivax, and mixed infection in Goa from 2000-2023. The spatiotemporal distribution of indigenous and imported malaria cases from 2014-2023 in the different primary/urban/community health centres (PHC/UHC/CHCs) of Goa was analysed using GIS. The spatiotemporal changes of the last three decades in Goa's land use/land cover (LU/LC) were assessed using Landsat satellite images, and its effect on malaria distribution was analysed.ResultsOver the study period (2000-2023), P. vivax contributed to 78.2% of the caseload. The malaria trend fluctuated from 2000 to 2008, with a steep decline observed from 2009 onwards, and in 2023, zero indigenous cases were reported. The six health centres of Candolim, Margao, Siolim, Vasco, Mapusa, and Panaji reported 57.8% of the total indigenous and imported malaria cases in Goa during 2014-2023. With 292 cases in 2023, the Porvorim UHC has emerged as a new hotspot of imported malaria cases. The LU/LC change analysis shows a four-fold increase of built-up area, from ~ 70 sq. km in 1991 to 260 sq. km in 2024, with strong spatial overlap between new built-up areas and malaria cases.ConclusionDue to the concerted parasite and vector control strategies of the state health department, Goa has achieved the target of zero indigenous malaria cases in 2023. Despite achieving this milestone, the threat of imported malaria cases leading to local outbreaks remains a serious concern.
| S-EPMC11829438 | biostudies-literature
Project description:IntroductionThe decision-making process for malaria control and elimination strategies has become more challenging. Interventions need to be targeted at council level to allow for changing malaria epidemiology and an increase in the number of possible interventions. Models of malaria dynamics can support this process by simulating potential impacts of multiple interventions in different settings and determining appropriate packages of interventions for meeting specific expected targets.MethodsThe OpenMalaria model of malaria dynamics was calibrated for all 184 councils in mainland Tanzania using data from malaria indicator surveys, school parasitaemia surveys, entomological surveillance, and vector control deployment data. The simulations were run for different transmission intensities per region and five interventions, currently or potentially included in the National Malaria Strategic Plan, individually and in combination. The simulated prevalences were fitted to council specific prevalences derived from geostatistical models to obtain council specific predictions of the prevalence and number of cases between 2017 and 2020. The predictions were used to evaluate in silico the feasibility of the national target of reaching a prevalence of below 1% by 2020, and to suggest alternative intervention stratifications for the country.ResultsThe historical prevalence trend was fitted for each council with an agreement of 87% in 2016 (95%CI: 0.84-0.90) and an agreement of 90% for the historical trend (2003-2016) (95%CI: 0.87-0.93) The current national malaria strategy was expected to reduce the malaria prevalence between 2016 and 2020 on average by 23.8% (95% CI: 19.7%-27.9%) if current case management levels were maintained, and by 52.1% (95% CI: 48.8%-55.3%) if the case management were improved. Insecticide treated nets and case management were the most cost-effective interventions, expected to reduce the prevalence by 25.0% (95% CI: 19.7%-30.2) and to avert 37 million cases between 2017 and 2020. Mass drug administration was included in most councils in the stratification selected for meeting the national target at minimal costs, expected to reduce the prevalence by 77.5% (95%CI: 70.5%-84.5%) and to avert 102 million cases, with almost twice higher costs than those of the current national strategy. In summary, the model suggested that current interventions are not sufficient to reach the national aim of a prevalence of less than 1% by 2020 and a revised strategic plan needs to consider additional, more effective interventions, especially in high transmission areas and that the targets need to be revisited.ConclusionThe methodology reported here is based on intensive interactions with the NMCP and provides a helpful tool for assessing the feasibility of country specific targets and for determining which intervention stratifications at sub-national level will have most impact. This country-led application could support strategic planning of malaria control in many other malaria endemic countries.
| S-EPMC7029840 | biostudies-literature
Project description:Anopheline mosquito insecticide resistance is a major threat to malaria control efforts and ultimately countries' ability to eliminate malaria. Using publicly available and published data we conducted spatial analyses to document and model the geo-spatial distribution of Anopheles gambiae s.l. insecticide resistance in Tanzania at national, regional, district and sub-district levels for the 2011 - 2017 period. We document anopheline mosquito resistance to all four major insecticide classes, with overall mosquito mortality declining from 2011 to 2016, and mean reductions of 1.6%, 0.5%, 0.4%, and 9.9% observed for organophosphates, carbamates, organochlorines and pyrethroids, respectively. An insecticide resistance map modeled for 2017 predicted that anopheline vector mortality was still above the 90% susceptibility threshold for all insecticide classes, except for pyrethroids. Using the model's output we calculated that resistance to organophosphates, carbamates, organochlorines, and pyrethroids is expected to exist in 11.6%, 15.6%, 8.1%, and 19.5% of Tanzania's territory, respectively, with areas in the Lake Zone and eastern Tanzania particularly affected. The methodology to predictively model available insecticide resistance data can readily be updated annually, allowing policy makers and malaria program management staff to continuously adjust their vector control approaches and plans, and determine where specific insecticides from various classes should be used to maximize intervention effectiveness.
| S-EPMC9393459 | biostudies-literature
Project description:BackgroundImported malaria continues to be reported in Sri Lanka after it was eliminated in 2012, and a few progress to life-threatening severe malaria.MethodsData on imported malaria cases reported in Sri Lanka from 2013 to 2023 were extracted from the national malaria database maintained by the Anti Malaria Campaign (AMC) of Sri Lanka. Case data of severe malaria as defined by the World Health Organization were analysed with regard to patients' general characteristics and their health-seeking behaviour, and the latter compared with that of uncomplicated malaria patients. Details of the last three cases of severe malaria in 2023 are presented.Results532 imported malaria cases were diagnosed over 11 years (2013-2023); 46 (8.6%) were severe malaria, of which 45 were Plasmodium falciparum and one Plasmodium vivax. Most severe malaria infections were acquired in Africa. All but one were males, and a majority (87%) were 26-60 years of age. They were mainly Sri Lankan nationals (82.6%). Just over half (56.5%) were treated at government hospitals. The average time between arrival of the person in Sri Lanka and onset of illness was 4 days. 29 cases of severe malaria were compared with 165 uncomplicated malaria cases reported from 2015 to 2023. On average both severe and uncomplicated malaria patients consulted a physician equally early (mean = 1 day) with 93.3% of severe malaria doing so within 3 days. However, the time from the point of consulting a physician to diagnosis of malaria was significantly longer (median 4 days) in severe malaria patients compared to uncomplicated patients (median 1 day) (p = 0.012) as was the time from onset of illness to diagnosis (p = 0.042). All severe patients recovered without sequelae except for one who died.ConclusionsThe risk of severe malaria among imported cases increases significantly beyond 5 days from the onset of symptoms. Although patients consult a physician early, malaria diagnosis tends to be delayed by physicians because it is now a rare disease. Good access to expert clinical care has maintained case fatality rates of severe malaria at par with those reported elsewhere.
| S-EPMC11193279 | biostudies-literature
Project description:BackgroundTanzania's Zanzibar archipelago has made significant gains in malaria control over the last decade and is a target for malaria elimination. Despite consistent implementation of effective tools since 2002, elimination has not been achieved. Importation of parasites from outside of the archipelago is thought to be an important cause of malaria's persistence, but this paradigm has not been studied using modern genetic tools.MethodsWhole-genome sequencing (WGS) was used to investigate the impact of importation, employing population genetic analyses of Plasmodium falciparum isolates from both the archipelago and mainland Tanzania. Ancestry, levels of genetic diversity and differentiation, patterns of relatedness, and patterns of selection between these two populations were assessed by leveraging recent advances in deconvolution of genomes from polyclonal malaria infections.ResultsSignificant decreases in the effective population sizes were inferred in both populations that coincide with a period of decreasing malaria transmission in Tanzania. Identity by descent analysis showed that parasites in the two populations shared long segments of their genomes, on the order of 5 cM, suggesting shared ancestry within the last 10 generations. Even with limited sampling, two of isolates between the mainland and Zanzibar were identified that are related at the expected level of half-siblings, consistent with recent importation.ConclusionsThese findings suggest that importation plays an important role for malaria incidence on Zanzibar and demonstrate the value of genomic approaches for identifying corridors of parasite movement to the island.
| S-EPMC6988337 | biostudies-literature