Genetic evidence for imported malaria and local transmission in Richard Toll, Senegal

Abstract Background: Malaria elimination efforts can be undermined by imported malaria infections. Imported infections are classified based on travel history.Methods: We applied a genetic strategy to better understand the contribution of imported infections and to test for local transmission in the very low prevalence region of Richard Toll, Senegal.Results: Genetic relatedness analysis, based upon molecular barcode genotyping data derived from diagnostic material, provided evidence for both imported infections and ongoing local transmission in Richard Toll. Evidence for imported malaria included finding that a large proportion of Richard Toll parasites were genetically related to parasites from Thiès, Senegal, a region of moderate transmission with extensive available genotyping data. Evidence for ongoing local transmission included finding parasites of identical genotype that persisted across multiple transmission seasons as well as enrichment of highly related infections within the households of non-travelers compared to travelers.Conclusions: These data indicate that, while a large number of infections may have been imported, there remains ongoing local malaria transmission in Richard Toll. These proof-of-concept findings underscore the value of genetic data to identify parasite relatedness and patterns of transmission to inform optimal intervention selection and placement. This work was supported by the Bill & Melinda Gates Foundation, Grant Number OPP1156051

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Genetic evidence for imported malaria and local transmission in Richard Toll, Senegal

10.21203/rs.2.24566/v3 ◽

2020 ◽

Author(s):

Sarah K. Volkman ◽

Oumar Sarr ◽

Richard W. Steketee ◽

Stephen F. Schaffner ◽

Yakou Dieye ◽

...

Keyword(s):

Genetic Relatedness ◽

Imported Malaria ◽

Travel History ◽

Intervention Selection ◽

Optimal Intervention ◽

Relatedness Analysis ◽

Molecular Barcode ◽

Low Prevalence ◽

Imported Infections ◽

Local Transmission

Abstract Background Malaria elimination efforts can be undermined by imported malaria infections. Imported infections are classified based on travel history. Methods A genetic strategy was applied to better understand the contribution of imported infections and to test for local transmission in the very low prevalence region of Richard Toll, Senegal. Results Genetic relatedness analysis, based upon molecular barcode genotyping data derived from diagnostic material, provided evidence for both imported infections and ongoing local transmission in Richard Toll. Evidence for imported malaria included finding that a large proportion of Richard Toll parasites were genetically related to parasites from Thiès, Senegal, a region of moderate transmission with extensive available genotyping data. Evidence for ongoing local transmission included finding parasites of identical genotype that persisted across multiple transmission seasons as well as enrichment of highly related infections within the households of non-travellers compared to travellers. Conclusions These data indicate that, while a large number of infections may have been imported, there remains ongoing local malaria transmission in Richard Toll. These proof-of-concept findings underscore the value of genetic data to identify parasite relatedness and patterns of transmission to inform optimal intervention selection and placement.

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Genetic evidence for imported malaria and local transmission in Richard Toll, Senegal

10.21203/rs.2.24566/v2 ◽

2020 ◽

Author(s):

Sarah K. Volkman ◽

Oumar Sarr ◽

Richard W. Steketee ◽

Stephen F. Schaffner ◽

Yakou Dieye ◽

...

Keyword(s):

Genetic Relatedness ◽

Imported Malaria ◽

Travel History ◽

Intervention Selection ◽

Optimal Intervention ◽

Relatedness Analysis ◽

Molecular Barcode ◽

Low Prevalence ◽

Imported Infections ◽

Local Transmission

Abstract Background: Malaria elimination efforts can be undermined by imported malaria infections. Imported infections are classified based on travel history. Methods: We applied a genetic strategy to better understand the contribution of imported infections and to test for local transmission in the very low prevalence region of Richard Toll, Senegal. Results: Genetic relatedness analysis, based upon molecular barcode genotyping data derived from diagnostic material, provided evidence for both imported infections and ongoing local transmission in Richard Toll. Evidence for imported malaria included finding that a large proportion of Richard Toll parasites were genetically related to parasites from Thiès, Senegal, a region of moderate transmission with extensive available genotyping data. Evidence for ongoing local transmission included finding parasites of identical genotype that persisted across multiple transmission seasons as well as enrichment of highly related infections within the households of non-travelers compared to travelers. Conclusions: These data indicate that, while a large number of infections may have been imported, there remains ongoing local malaria transmission in Richard Toll. These proof-of-concept findings underscore the value of genetic data to identify parasite relatedness and patterns of transmission to inform optimal intervention selection and placement.

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The impact of mass drug administration expansion to low onchocerciasis prevalence settings in case of connected villages

PLoS Neglected Tropical Diseases ◽

10.1371/journal.pntd.0009011 ◽

2021 ◽

Vol 15 (5) ◽

pp. e0009011

Author(s):

Anneke S. de Vos ◽

Wilma A. Stolk ◽

Luc E. Coffeng ◽

Sake J. de Vlas

Keyword(s):

Intermediate Host ◽

Drug Administration ◽

Mass Drug Administration ◽

Human Populations ◽

Individual Based Model ◽

Low Prevalence ◽

The Impact ◽

Local Transmission

Background The existence of locations with low but stable onchocerciasis prevalence is not well understood. An often suggested yet poorly investigated explanation is that the infection spills over from neighbouring locations with higher infection densities. Methodology We adapted the stochastic individual based model ONCHOSIM to enable the simulation of multiple villages, with separate blackfly (intermediate host) and human populations, which are connected through the regular movement of the villagers and/or the flies. With this model we explore the impact of the type, direction and degree of connectedness, and of the impact of localized or full-area mass drug administration (MDA) over a range of connected village settings. Principal findings In settings with annual fly biting rates (ABR) below the threshold needed for stable local transmission, persistence of onchocerciasis prevalence can well be explained by regular human traffic and/or fly movement from locations with higher ABR. Elimination of onchocerciasis will then theoretically be reached by only implementing MDA in the higher prevalence area, although lingering infection in the low prevalence location can trigger resurgence of transmission in the total region when MDA is stopped too soon. Expanding MDA implementation to the lower ABR location can therefore shorten the duration of MDA needed. For example, when prevalence spill-over is due to human traffic, and both locations have about equal populations, then the MDA duration can be shortened by up to three years. If the lower ABR location has twice as many inhabitants, the reduction can even be up to six years, but if spill-over is due to fly movement, the expected reduction is less than a year. Conclusions/Significance Although MDA implementation might not always be necessary in locations with stable low onchocerciasis prevalence, in many circumstances it is recommended to accelerate achieving elimination in the wider area.

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