High heterogeneity of malaria transmission and a large sub-patent and diverse reservoir of infection in Wusab As Safil district, Republic of Yemen

Cook, Jackie; Grignard, Lynn; Al-Eryani, Samira; Al-Selwei, Mustafa; Mnzava, Abraham; Al-Yarie, Hafed; Rand, Alison; Kleinschmidt, Immo; Drakeley, Chris

doi:10.1186/s12936-016-1249-y

Cited by 12 publications

(6 citation statements)

References 40 publications

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“…The overall P. falciparum and P. vivax seroprevalence presented here (13 and 10 %, respectively) was lower than previously described levels in other countries in the Eastern Mediterranean region, such as Somalia (18 and 19 %) [ 6 ], Djibouti (32 and 3 %, adults only) [ 29 ], and Yemen (32 and 3 %, children only) [ 30 ]. These studies took place between 2002 and 2011, while the data presented here are from 2012.…”

Section: Discussioncontrasting

confidence: 77%

Anti-malarial seroprevalence assessment during an elimination programme in Chabahar District, south-eastern Iran

Zakeri

Hoogen

Mehrizi

et al. 2016

Malar J

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BackgroundIran has achieved a substantial decline in malaria incidence over the past decades. A common feature of malaria-endemic settings is the requirement for more sensitive techniques to describe levels of low transmission. In this study, serological and parasitological methods were used to measure transmission levels of Plasmodium falciparum and Plasmodium vivax during an elimination programme (2012) in Chabahar District, Sistan and Baluchistan Province, south-eastern Iran.MethodsParticipants were randomly selected from 64 different geographical clusters in Chabahar city and surrounding villages. Antibody responses to P. falciparum and P. vivax blood-stage antigens were assessed by ELISA, while microscopy and molecular testing were used to determine parasite carriage by species. Age-adjusted antibody responses were analysed using a reversible catalytic model to calculate seroconversion rates (SCR).ResultsThere was no evidence of recent transmission in the study areas, indicated by an absence of parasite infections in all ages and low or absent serological responses to either species in young children. The best model for age P. falciparum seroconversion was one with a change in exposure 21 years before sampling was done in Chabahar city (P = 0.018) and 4 years in the villages (P = 0.039). There was a higher level of recent P. vivax transmission compared to P. falciparum, based on the SCRs, in both the city and village settings.ConclusionSerological analysis identified a decline in P. falciparum transmission in the urban areas of Chabahar, consistent with a previously described decrease in malaria in the early 1990s, demonstrating the utility of this approach to reconstruct exposure history. At present, it remains unclear whether the P. vivax antibody responses reflect active transmission due to new infections or relapse infections. The absence of parasitological and serological evidence of recent malaria transmission in Chabahar District is viable evidence for certification of elimination.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1432-1) contains supplementary material, which is available to authorized users.

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Section: Discussioncontrasting

confidence: 77%

Anti-malarial seroprevalence assessment during an elimination programme in Chabahar District, south-eastern Iran

Zakeri

Hoogen

Mehrizi

et al. 2016

Malar J

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“…As documented in other settings, declining transmission leads to increasing transmission heterogeneity [60, 62] and an increasing proportion of asymptomatic low-density infections [6–8]. In 2013, over two thirds all PCR-detected infections were sub-microscopic and the risk of clinical malaria was highly dependent on where the child lived, with higher risk of clinical illness observed in areas with higher force of infection.…”

Section: Discussionmentioning

confidence: 96%

Differential impact of malaria control interventions on P. falciparum and P. vivax infections in young Papua New Guinean children

Ome-Kaius

Kattenberg

Zaloumis

et al. 2019

BMC Med

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IntroductionAs malaria transmission declines, understanding the differential impact of intensified control on Plasmodium falciparum relative to Plasmodium vivax and identifying key drivers of ongoing transmission is essential to guide future interventions.MethodsThree longitudinal child cohorts were conducted in Papua New Guinea before (2006/2007), during (2008) and after scale-up of control interventions (2013). In each cohort, children aged 1–5 years were actively monitored for infection and illness. Incidence of malaria episodes, molecular force of blood-stage infections (molFOB) and population-averaged prevalence of infections were compared across the cohorts to investigate the impact of intensified control in young children and the key risk factors for malaria infection and illness in 2013.ResultsBetween 2006 and 2008, P. falciparum infection prevalence, molFOB, and clinical malaria episodes reduced by 47%, 59% and 69%, respectively, and a further 49%, 29% and 75% from 2008 to 2013 (prevalence 41.6% to 22.1% to 11.2%; molFOB: 3.4 to 1.4 to 1.0 clones/child/year; clinical episodes incidence rate (IR) 2.6 to 0.8 to IR 0.2 episodes/child/year). P. vivax clinical episodes declined at rates comparable to P. falciparum between 2006, 2008 and 2013 (IR 2.5 to 1.1 to 0.2), while P. vivax molFOB (2006, 9.8; 2008, 12.1) and prevalence (2006, 59.6%; 2008, 65.0%) remained high in 2008. However, in 2013, P. vivax molFOB (1.2) and prevalence (19.7%) had also substantially declined. In 2013, 89% of P. falciparum and 93% of P. vivax infections were asymptomatic, 62% and 47%, respectively, were sub-microscopic. Area of residence was the major determinant of malaria infection and illness.ConclusionIntensified vector control and routine case management had a differential impact on rates of P. falciparum and P. vivax infections but not clinical malaria episodes in young children. This suggests comparable reductions in new mosquito-derived infections but a delayed impact on P. vivax relapsing infections due to a previously acquired reservoir of hypnozoites. This demonstrates the need to strengthen implementation of P. vivax radical cure to maximise impact of control in co-endemic areas. The high heterogeneity of malaria in 2013 highlights the importance of surveillance and targeted interventions to accelerate towards elimination.

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“…Following the parasite genetic signature to link infections in time and space could confirm the presence of hotspots and quantify the extent to which they seed transmission outside hotspot boundaries [59]. Parasite genetic tools have been able to identify the source and routes of propagation of malaria between communities, particularly in relation to population movement [60,61]. However, to address the question of hotspots, transmission dynamics within villages are most relevant, ideally capturing both local human movement and the time and location of all new parasites' genetic barcode [62].…”

Section: Transmission Intensity Amentioning

confidence: 99%

Malaria Hotspots: Is There Epidemiological Evidence for Fine-Scale Spatial Targeting of Interventions?

Stresman

Bousema

Cook

2019

Trends in Parasitology

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As data at progressively granular spatial scales become available, the temptation is to target interventions to areas with higher malaria transmission -so-called hotspots -with the aim of reducing transmission in the wider community. This paper reviews literature to determine if hotspots are an intrinsic feature of malaria epidemiology and whether current evidence supports hotspot-targeted interventions. Hotspots are a consistent feature of malaria transmission at all endemicities. The smallest spatial unit capable of supporting transmission is the household, where peri-domestic transmission occurs. Whilst the value of focusing interventions to highburden areas is evident, there is currently limited evidence that local-scale hotspots fuel transmission. As boundaries are often uncertain, there is no conclusive evidence that hotspot-targeted interventions accelerate malaria elimination.

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High heterogeneity of malaria transmission and a large sub-patent and diverse reservoir of infection in Wusab As Safil district, Republic of Yemen

Cited by 12 publications

References 40 publications

Anti-malarial seroprevalence assessment during an elimination programme in Chabahar District, south-eastern Iran

Anti-malarial seroprevalence assessment during an elimination programme in Chabahar District, south-eastern Iran

Differential impact of malaria control interventions on P. falciparum and P. vivax infections in young Papua New Guinean children

Malaria Hotspots: Is There Epidemiological Evidence for Fine-Scale Spatial Targeting of Interventions?

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