The Relative Contribution of Symptomatic and Asymptomatic Plasmodium vivax and Plasmodium falciparum Infections to the Infectious Reservoir in a Low-Endemic Setting in Ethiopia

Tadesse, Fitsum G.; Slater, Hannah; Chali, Wakweya; Teelen, Karina; Lanke, Kjerstin; Belachew, Mulualem; Menberu, Temesgen; Shumie, Girma; Shitaye, Getasew; Okell, Lucy; Graumans, Wouter; Gemert, Geert-Jan van; Kedir, Soriya; Tesfaye, Addisu; Belachew, Feleke; Abebe, Wake; Mamo, Hassen; Sauerwein, Robert W.; Balcha, Taye Tolera; Aseffa, Abraham; Yewhalaw, Delenasaw; Gadisa, Endalamaw; Drakeley, Chris; Bousema, Teun

doi:10.1093/cid/cix1123

Cited by 145 publications

(157 citation statements)

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“…stephensi . We recruited fewer clinical P. falciparum cases who, in line with other findings, were less likely to infect mosquitoes compared to P. vivax patients [31]. Despite a modest number of observations, our findings demonstrate that also local P. falciparum isolates are capable of infecting An.…”

Section: Discussionsupporting

confidence: 63%

“…stephensi to naturally circulating Plasmodium parasites from malaria patients via membrane feeding in comparison to an established and membrane-adapted colony of An. arabiensis [31]. Our mosquito feeding experiments predominantly included P. vivax clinical cases who are highly infective [31, 32], and allow a sensitive comparison of mosquito species.…”

Section: Discussionmentioning

confidence: 99%

“…arabiensis [31]. Our mosquito feeding experiments predominantly included P. vivax clinical cases who are highly infective [31, 32], and allow a sensitive comparison of mosquito species. Although the membrane adapted colony of An.…”

Section: Discussionmentioning

confidence: 99%

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Anopheles stephensi as an emerging malaria vector in the Horn of Africa with high susceptibility to Ethiopian Plasmodium vivax and Plasmodium falciparum isolates

Ashine

Teka

Esayas

et al. 2020

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Anopheles stephensi, an efficient Asian malaria vector, recently spread into the Horn of Africa and may increase malaria receptivity in African urban areas. We assessed occurrence, genetic complexity, blood meal source and infection status of An. stephensi in Awash Sebat Kilo town, Ethiopia. We used membrane feeding assays to assess competence of local An. stephensi to P. vivax and P. falciparum isolates from clinical patients. 75.3% of the examined waterbodies were infested with An. stephensi developmental stages that were genetically closely related to isolates from Djibouti and Pakistan. Both P. vivax and P. falciparum were detected in wild-caught adult An. stephensi. Local An. stephensi was more receptive to P. vivax compared to a colony of An. arabiensis. We conclude that An. stephensi is an established vector in this part of Ethiopia, highly permissive for local P. vivax and P. falciparum isolates and presents an important new challenge for malaria control.Summary of the articleAn. stephensi, a metropolitan malaria vector that recently expanded to the Horn of African, was highly susceptible to local P. falciparum and P. vivax isolates from Ethiopia and may increase malariogenic potential of rapidly expanding urban settings in Africa.

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Section: Discussionsupporting

confidence: 63%

Section: Discussionmentioning

confidence: 99%

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Anopheles stephensi as an emerging malaria vector in the Horn of Africa with high susceptibility to Ethiopian Plasmodium vivax and Plasmodium falciparum isolates

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Teka

Esayas

et al. 2020

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“…Records published January 2010 -July 2017 were searched, yielding 2136 records. A 6 further two records, unpublished at the time of screening, were also included 19,27 , as were additional 7 data collected through contacting authors of included references. Studies reporting asexual 8 P.falciparum prevalence by microscopy and PCR in the same population were included.…”

Section: Systematic Review Update and Data Extractionmentioning

confidence: 99%

Global & Temporal Patterns of Submicroscopic Plasmodium falciparum Malaria Infection

Whittaker

Slater

Bousema

et al. 2019

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Background: Adoption of molecular techniques to detect Plasmodium falciparum infection has revealed many 11 previously undetected (yet transmissible) low-density infections in areas of low malaria transmission. In a world 12 where numerous countries are approaching elimination, additional data from low transmission areas are 13 required to better understand the determinants of submicroscopic infection and their potential relevance in 14 these settings. 15Methods: We updated a systematic review of studies assessing asexual P. falciparum prevalence by microscopy 16 and PCR in the same population. PubMed and Web of Science databases were searched up to July 2017. Bayesian Research in Context:1 Evidence before this study: Cross-sectional studies of malaria prevalence in endemic populations have revealed 2 the widespread presence of infections with parasite densities lower than the threshold of detection by 3 microscopy. Previous systematic reviews of these surveys have highlighted that the fraction of P.falciparum 4 infections missed by microscopy can be substantial (~45% of all infections detected by PCR on average), that 5 submicroscopic infection is more likely in adults than in children (a phenomenon attributed to increased levels 6 of immunity), and that this missed fraction (the "submicroscopic reservoir") is typically highest in areas with low 7 transmission intensity. Although further work is required, a number of studies have also demonstrated the 8 capacity of these submicroscopic, low density infections to infect mosquitoes and therefore contribute to 9 onwards transmission. 10Added value of this study: Although previous studies have found that infections in older, more immune 11 individuals are more likely to be submicroscopic, in lower transmission settings where individuals generally 12 develop less immunity, a larger proportion of infections are also typically submicroscopic. Here we present an 13 updated systematic review to explore this apparent paradox across a range of transmission settings and define 14 contexts in which submicroscopic infections are likely to be most relevant to malaria control efforts. Leveraging 15 the substantial increase in the availability of malaria cross-sectional surveys reporting prevalence by molecular 16 methods, we explore the association of submicroscopic infection with a number of novel factors -these include

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“…First, we assume individuals with asymptomatic infections to be 2, 10 and 30 times less infectious to mosquitoes than individuals with symptomatic infections (relative infectiousness ( RI ) of 1/2, 1/10 and 1/30, respectively). Empirical RI estimates vary widely according to the average gametocyte density [24] and are close to 1/2 for microscopy-detected asymptomatic P. vivax infections in Ethiopia [25] but range from 1/14 to 1/29 for asymptomatic infections in Colombia and Brazil that can be detected only by molecular methods [26, 27].…”

Section: Methodsmentioning

confidence: 99%

Modelling the epidemiology of residual Plasmodium vivax malaria in a heterogeneous host population: a case study in the Amazon Basin

Corder

Ferreira

Gomes

2019

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15 The overall malaria burden in the Americas has decreased dramatically over the past two 16 decades, but residual transmission pockets persist across the Amazon Basin, where 17 Plasmodium vivax is the predominant infecting species. Current elimination efforts require a 18 better quantitative understanding of malaria transmission dynamics for planning, monitoring, 19 and evaluating interventions at the community level. This can be achieved with mathematical 20 models that properly account for risk heterogeneity in communities approaching elimination, 21 where few individuals disproportionately contribute to overall malaria prevalence, morbidity, 22 and onwards transmission. Here we analyse demographic information combined with 23 routinely collected malaria morbidity data from the town of Mâncio Lima, the main urban 24 transmission hotspot of Brazil. We estimate the proportion of high-risk subjects in the host 25 population by fitting compartmental susceptible-infected-susceptible (SIS) transmission 26 models simultaneously to age-stratified vivax malaria incidence densities and the frequency 27 distribution of P. vivax malaria attacks experienced by each individual over 12 months.28 Simulations with the best-fitting SIS model indicate that 20% of the hosts contribute 86% of 29 the overall vivax malaria burden. Despite the low overall force of infection typically found in 30 the Amazon, about one order of magnitude lower than that in rural Africa, high-risk individuals 31 gradually develop clinical immunity following repeated infections and eventually constitute a 32 substantial infectious reservoir comprised of asymptomatic parasite carriers that is overlooked 33 by routine surveillance but likely fuels onwards malaria transmission. High-risk individuals 34 therefore represent a priority target for more intensive and effective interventions that may 35 not be readily delivered to the entire community. 36 3 37 Keywords: Mathematical modelling, urban malaria, heterogeneity, Amazon, hotspots, 38 asymptomatic infection. 39 4 40 Introduction 41 Heterogeneity in the risk of infection with several pathogens has been repeatedly documented 42 in human populations, with 20% of the hosts typically harbouring 80% of the pathogen burden 43 in the community [1]. For example, residents in the same village in rural Africa may greatly 44 differ in their malaria risk, leading to over-dispersed frequency distributions of malaria attacks 45 per person over time, with few subjects in the community experiencing frequent infection and 46 disease [2]. 4748 One source of malaria risk heterogeneity is the varying hosts' exposure to the pathogen, which 49 can be measured as the number of infectious mosquito bites per host per unit of time, termed 50 the entomological inoculation rate (EIR). About 20% of the children are estimated to receive 51 80% of all infectious mosquito bites in rural African settings, suggesting that malaria parasites 52 may also conform to the "20/80 rule" [3]. Significant malaria risk heterogeneity has also been 5...

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The Relative Contribution of Symptomatic and Asymptomatic Plasmodium vivax and Plasmodium falciparum Infections to the Infectious Reservoir in a Low-Endemic Setting in Ethiopia

Abstract: In this low-endemic setting aiming for malaria elimination, asymptomatic infections were highly prevalent and responsible for the majority of onward mosquito infections. The early identification and treatment of asymptomatic infections might accelerate elimination efforts.

Cited by 145 publications

References 28 publications

Anopheles stephensi as an emerging malaria vector in the Horn of Africa with high susceptibility to Ethiopian Plasmodium vivax and Plasmodium falciparum isolates

Anopheles stephensi as an emerging malaria vector in the Horn of Africa with high susceptibility to Ethiopian Plasmodium vivax and Plasmodium falciparum isolates

Global & Temporal Patterns of Submicroscopic Plasmodium falciparum Malaria Infection

Modelling the epidemiology of residual Plasmodium vivax malaria in a heterogeneous host population: a case study in the Amazon Basin

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