19 results found
Sherrard-Smith E, Skarp JE, Beale AD, et al., Mosquito feeding behavior and how it influences residual malaria transmission across Africa, Proceedings of the National Academy of Sciences, ISSN: 0027-8424
Green N, Sherrard-Smith E, Tanton C, et al., 2019, Assessing local chlamydia screening performance by combining survey and administrative data to account for differences in local population characteristics, Scientific Reports, Vol: 9, ISSN: 2045-2322
Reducing health inequalities requires improved understanding of the causes of variation. Local-level variation reflects differences in local population characteristics and health system performance. Identifying low- and high-performing localities allows investigation into these differences. We used Multilevel Regression with Post-stratification (MRP) to synthesise data from multiple sources, using chlamydia testing as our example. We used national probability survey data to identify individual-level characteristics associated with chlamydia testing and combined this with local-level census data to calculate expected levels of testing in each local authority (LA) in England, allowing us to identify LAs where observed chlamydia testing rates were lower or higher than expected, given population characteristics. Taking account of multiple covariates, including age, sex, ethnicity, student and cohabiting status, 5.4% and 3.5% of LAs had testing rates higher than expected for 95% and 99% posterior credible intervals, respectively; 60.9% and 50.8% had rates lower than expected. Residual differences between observed and MRP expected values were smallest for LAs with large proportions of non-white ethnic populations. London boroughs that were markedly different from expected MRP values (90% posterior exceedance probability) had actively targeted risk groups. This type of synthesis allows more refined inferences to be made at small-area levels than previously feasible.
Suh E, Grossman MK, Waite JL, et al., 2019, Thermal ecology of malaria transmission and the potential impact of behavioural resistance, Publisher: Cold Spring Harbor Laboratory
<jats:title>Abstract</jats:title><jats:p>A number of studies report changes in the biting time of malaria mosquitoes following the introduction of long-lasting insecticide-treated bed nets (LLINs). Here, we explored whether timing of blood feeding interacts with environmental temperature to influence the vector competence of <jats:italic>Anopheles</jats:italic> mosquitoes for the human malaria parasite, <jats:italic>Plasmodium falciparum</jats:italic>. We found no effect of biting time on the proportion of mosquitoes that became infectious at constant temperature. However, the addition of realistic daily temperature fluctuation reduced the vector competence of mosquitoes feeding in the morning and increased the competence of those feeding in the early evening. A transmission dynamics model illustrates that such changes could have important implications for the epidemiological impact of “behavioural resistance”. A shift in mosquito biting to the morning could reduce the transmission probability, and so poses little epidemiological risk. However, an increase in early evening biting could increase transmission not only because people are unprotected by bed nets, but also because there is a higher chance of blood-feeding mosquito becoming infectious.</jats:p>
Sherrard-Smith E, Griffin J, Winskill P, et al., 2018, Systematic review of indoor residual spray efficacy and effectiveness against Plasmodium falciparum in Africa, Nature Communications, Vol: 9, ISSN: 2041-1723
Indoor residual spraying (IRS) is an important part of malaria control. There is a growing list of insecticide classes; pyrethroids remain the principal insecticide used in bednets but recently, novel non-pyrethroid IRS products, with contrasting impacts, have been introduced. There is an urgent need to better assess product efficacy to help decision makers choose effective and relevant tools for mosquito control. Here we use experimental hut trial data to characterise the entomological efficacy of widely-used, novel IRS insecticides. We quantify their impact against pyrethroid-resistant mosquitoes and use a Plasmodium falciparum transmission model to predict the public health impact of different IRS insecticides. We report that long-lasting IRS formulations substantially reduce malaria, though their benefit over cheaper, shorter-lived formulations depends on local factors including bednet use, seasonality, endemicity and pyrethroid resistance status of local mosquito populations. We provide a framework to help decision makers evaluate IRS product effectiveness.
Witmer K, Sherrard-Smith E, Straschil U, et al., 2018, An inexpensive open source 3D printed membrane feeder for human malaria transmission studies, Malaria Journal, Vol: 17, ISSN: 1475-2875
BackgroundThe study of malaria transmission requires the experimental infection of mosquitoes with Plasmodium gametocytes. In the laboratory, this is achieved using artificial membrane feeding apparatus that simulate body temperature and skin of the host, and so permit mosquito feeding on reconstituted gametocyte-containing blood. Membrane feeders either use electric heating elements or complex glass chambers to warm the infected blood; both of which are expensive to purchase and can only be sourced from a handful of specialized companies. Presented and tested here is a membrane feeder that can be inexpensively printed using 3D-printing technology.ResultsUsing the Plasmodium falciparum laboratory strain NF54, three independent standard membrane feeding assays (SMFAs) were performed comparing the 3D-printed feeder against a commercial glass feeder. Exflagellation rates did not differ between the two feeders. Furthermore, no statistically significant difference was found in the oocyst load nor oocyst intensity of Anopheles stephensi mosquitoes (mean oocyst range 1.3–6.2 per mosquito; infection prevalence range 41–79%).ConclusionsOpen source provision of the design files of the 3D-printed feeder will facilitate a wider range of laboratories to perform SMFAs in laboratory and field settings, and enable them to freely customize the design to their own requirements.
Sherrard-Smith E, Sala KA, Betancourt M, et al., 2018, Synergy in anti-malarial pre-erythrocytic and transmission-blocking antibodies is achieved by reducing parasite density, eLife, Vol: 7, ISSN: 2050-084X
Anti-malarial pre-erythrocytic vaccines (PEV) target transmission by inhibiting human infection but are currently partially protective. It has been posited, but never demonstrated, that co-administering transmission-blocking vaccines (TBV) would enhance malaria control. We hypothesized a mechanism that TBV could reduce parasite density in the mosquito salivary glands, thereby enhancing PEV efficacy. This was tested using a multigenerational population assay, passaging Plasmodium berghei to Anopheles stephensi mosquitoes. A combined efficacy of 90.8% (86.7–94.2%) was observed in the PEV +TBV antibody group, higher than the estimated efficacy of 83.3% (95% CrI 79.1–87.0%) if the two antibodies acted independently. Higher PEV efficacy at lower mosquito parasite loads was observed, comprising the first direct evidence that co-administering anti-sporozoite and anti-transmission interventions act synergistically, enhancing PEV efficacy across a range of TBV doses and transmission intensities. Combining partially effective vaccines of differing anti-parasitic classes is a pragmatic, powerful way to accelerate malaria elimination efforts.
O'Brien A, Sherrard-Smith E, Sile B, et al., 2018, Spatial clusters of gonorrhoea in England with particular reference to the outcome of partner notification: 2012 and 2013, PLoS ONE, Vol: 13, ISSN: 1932-6203
Background:This study explored spatial-temporal variation in diagnoses of gonorrhoea to identify and quantify endemic areas and clusters in relation to patient characteristics and outcomes of partner notification (PN) across England, UK.Methods:Endemic areas and clusters were identified using a two-stage analysis with Kulldorff’s scan statistics (SaTScan).ResultsOf 2,571,838 tests, 53,547 diagnoses were gonorrhoea positive (positivity = 2.08%). The proportion of diagnoses in heterosexual males was 1.5 times that in heterosexual females. Among index cases, men who have sex with men (MSM) were 8 times more likely to be diagnosed with gonorrhoea than heterosexual males (p<0.0001). After controlling for age, gender, ethnicity and deprivation rank, 4 endemic areas were identified including 11,047 diagnoses, 86% of which occurred in London. 33 clusters included 17,629 diagnoses (34% of total diagnoses in 2012 and 2013) and spanned 21 locations, some of which were dominated by heterosexually acquired infection, whilst others were MSM focused. Of the 53,547 diagnoses, 14.5% (7,775) were the result of PN. The proportion of patients who attended services as a result of PN varied from 0% to 61% within different age, gender and sexual orientation cohorts. A third of tests resulting from PN were positive for gonorrhoea. 25% of Local Authorities (n = 81, 95% CI: 20.2, 29.5) had a higher than expected proportion for female PN diagnoses as compared to 16% for males (n = 52, 95% CI: 12.0, 19.9).Conclusions:The English gonorrhoea epidemic is characterised by spatial-temporal variation. PN success varied between endemic areas and clusters. Greater emphasis should be placed on the role of PN in the control of gonorrhoea to reduce the risk of onward transmission, re-infection, and complications of infection.
Sherrard-Smith E, Churcher TS, Upton LM, et al., 2017, A novel model itted to multiple life stages of malaria for assessing eicacy of transmission-blocking interventions, Malaria Journal, Vol: 16, ISSN: 1475-2875
BackgroundTransmission-blocking interventions (TBIs) aim to eliminate malaria by reducing transmission of the parasite between the host and the invertebrate vector. TBIs include transmission-blocking drugs and vaccines that, when given to humans, are taken up by mosquitoes and inhibit parasitic development within the vector. Accurate methodologies are key to assess TBI efficacy to ensure that only the most potent candidates progress to expensive and time-consuming clinical trials. Measuring intervention efficacy can be problematic because there is substantial variation in the number of parasites in both the host and vector populations, which can impact transmission even in laboratory settings.MethodsA statistically robust empirical method is introduced for estimating intervention efficacy from standardised population assay experiments. This method will be more reliable than simple summary statistics as it captures changes in parasite density in different life-stages. It also allows efficacy estimates at a finer resolution than previous methods enabling the impact of the intervention over successive generations to be tracked. A major advantage of the new methodology is that it makes no assumptions on the population dynamics of infection. This enables both host-to-vector and vector-to-host transmission to be density-dependent (or other) processes and generates easy-to-understand estimates of intervention efficacy.ResultsThis method increases the precision of intervention efficacy estimates and demonstrates that relying on changes in infection prevalence (the proportion of infected hosts) alone may be insufficient to capture the impact of TBIs, which also suppress parasite density in secondarily infected hosts.ConclusionsThe method indicates that potentially useful, partially effective TBIs may require multiple infection cycles before substantial reductions in prevalence are observed, despite more rapidly suppressing parasite density. Accurate models to quantify effica
Sitko J, Bizos J, Sherrard-Smith E, et al., 2016, Integrative taxonomy of European parasitic flatworms of the genus Metorchis Looss, 1899 (Trematoda: Opisthorchiidae), Parasitology International, Vol: 65, Pages: 258-267, ISSN: 1873-0329
Sherrard-Smith E, Stanton DWG, Cable J, et al., 2015, Distribution and molecular phylogeny of biliary trematodes (Opisthorchiidae) infecting native Lutra lutra and alien Neovison vison across Europe, Parasitology International, Vol: 65, Pages: 163-170, ISSN: 1873-0329
The recent identification of Pseudamphistomum truncatum, (Rudolphi, 1819) (Trematoda: Opisthorchiidae) and Metorchis bilis (Braun, 1790) Odening, 1962 (synonymous with Metorchis albidus (Braun, 1893) Loos, 1899 and Metorchis crassiusculus (Rudolphi, 1809) Looss, 1899 (Trematoda: Opisthorchiidae)) in otters from Britain caused concern because of associated biliary damage, coupled with speculation over their alien status. Here, we investigate the presence, intensity and phylogeny of these trematodes in mustelids (principally otters) across Europe (Czech Republic, Denmark, France, Germany, Norway, Poland and Sweden and Britain). The trematodes were identified to species using the internal transcribed spacer II (ITS2) locus. Both parasites were found across Europe but at unequal frequency. In the German state of Saxony, eight out of eleven (73%) otters examined were infected with P. truncatum whilst this parasite was not found in either mink from Scotland (n = 40) or otters from Norway (n = 21). Differences in the phylogenies between the two species suggest divergent demographic histories possibly reflecting contrasting host diet or competitive exclusion, with M. bilis exhibiting greater mitochondrial diversity than P. truncatum. Shared haplotypes within the ranges of both parasite species probably reflect relatively unrestricted movements (both natural and anthropogenic) of intermediate and definitive hosts across Europe.
Harding-Esch E, Sherrard-Smith E, Fuller SS, et al., 2015, SEXUAL BEHAVIOUR IN THE TIME PERIOD BETWEEN BEING TESTED FOR CHLAMYDIA AND RECEIVING TEST RESULT AND TREATMENT, Publisher: BMJ PUBLISHING GROUP, Pages: A37-A37, ISSN: 1368-4973
Sherrard-Smith E, Chadwick EA, Cable J, 2015, The impact of introduced hosts on parasite transmission: opisthorchiid infections in American mink (Neovison vison), BIOLOGICAL INVASIONS, Vol: 17, Pages: 115-122, ISSN: 1387-3547
Sherrard-Smith E, Perkins SE, Chadwick EA, et al., 2015, Spatial and seasonal factors are key determinants in the aggregation of helminths in their definitive hosts: Pseudamphistomum truncatum in otters (Lutra lutra), INTERNATIONAL JOURNAL FOR PARASITOLOGY, Vol: 45, Pages: 75-83, ISSN: 0020-7519
Bluemel JK, Derlink M, Pavlovcic P, et al., 2014, Integrating vibrational signals, mitochondrial DNA andmorphology for species determination in the genus Aphrodes (Hemiptera: Cicadellidae), SYSTEMATIC ENTOMOLOGY, Vol: 39, Pages: 304-324, ISSN: 0307-6970
Sherrard-Smith E, Chadwick EA, Cable J, 2013, Climatic variables are associated with the prevalence of biliary trematodes in otters, INTERNATIONAL JOURNAL FOR PARASITOLOGY, Vol: 43, Pages: 729-737, ISSN: 0020-7519
Chadwick EA, Cable J, Chinchen A, et al., 2013, Seroprevalence of toxoplasma gondii in the Eurasian otter (lutra lutra) in England and Wales, Parasites & Vectors, Vol: 6, ISSN: 1756-3305
BackgroundToxoplasma gondii is found on all continents and can infect all endothermic vertebrates. Toxoplasmosis is a globally important zoonosis with potentially devastating health impacts both for humans and a range of domestic and wild species. The World Health Organisation have repeatedly recommended the collection of accurate epidemiological data for T. gondii, yet despite recognised links between infection of wildlife, domestic animals and humans, seroprevalence in wild species is rarely monitored. Here, serological investigation using the Gold Standard Sabin-Feldman Dye Test was used to test for T. gondii in Eurasian otters (Lutra lutra) found dead, mainly as road-kill, in England and Wales. This is the first spatially widespread study of T. gondii in UK wildlife, and the first extensive survey of T. gondii in Eurasian otters, a sentinel species of fresh waters.FindingsInfection was both common (39.5% prevalence, n = 271) and widespread, with significantly more infection in the east than the west of the UK. There was an increase in seroprevalence with age, but no sex bias.ConclusionsThe relatively high prevalence of T. gondii in a predominantly piscivorous freshwater mammal suggests widespread faecal contamination of freshwater ecosystems with oocysts. Continued surveillance of the Eurasian otter for T. gondii is valuable because of conservation concerns due to the otter’s ‘near threatened’ status on the IUCN Red List and because of the host’s role as a sentinel for freshwater health.
Sherrard-Smith E, Chadwick E, Cable J, 2012, Abiotic and Biotic Factors Associated with Tick Population Dynamics on a Mammalian Host: Ixodes hexagonus Infesting Otters, Lutra lutra, PLOS ONE, Vol: 7, ISSN: 1932-6203
Sherrard-Smith E, Cable J, Chadwick EA, 2009, Distribution of Eurasian otter biliary parasites, Pseudamphistomum truncatum and Metorchis albidus (Family Opisthorchiidae), in England and Wales, PARASITOLOGY, Vol: 136, Pages: 1015-1022, ISSN: 0031-1820
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