174 results found
This article reviews research on the evolutionary mechanisms leading to different transmission modes. Such modes are often under genetic control of the host or the pathogen, and often in conflict with each other via trade-offs. Transmission modes may vary among pathogen strains and among host populations. Evolutionary changes in transmission mode have been inferred through experimental and phylogenetic studies, including changes in transmission associated with host shifts and with evolution of the unusually complex life cycles of many parasites. Understanding the forces that determine the evolution of particular transmission modes presents a fascinating medley of problems for which there is a lack of good data and often a lack of conceptual understanding or appropriate methodologies. Our best information comes from studies that have been focused on the vertical versus horizontal transmission dichotomy. With other kinds of transitions, theoretical approaches combining epidemiology and population genetics are providing guidelines for determining when and how rapidly new transmission modes may evolve, but these are still in need of empirical investigation and application to particular cases. Obtaining such knowledge is a matter of urgency in relation to extant disease threats.This article is part of the themed issue 'Opening the black box: re-examining the ecology and evolution of parasite transmission'.
Borlase A, Webster JP, Rudge JW, 2017, Opportunities and challenges for modelling epidemiological and evolutionary dynamics in a multihost, multiparasite system: Zoonotic hybrid schistosomiasis in West Africa, Evolutionary Applications, ISSN: 1752-4563
© 2017 John Wiley & Sons Ltd. Multihost multiparasite systems are evolutionarily and ecologically dynamic, which presents substantial trans-disciplinary challenges for elucidating their epidemiology and designing appropriate control. Evidence for hybridizations and introgressions between parasite species is gathering, in part in line with improvements in molecular diagnostics and genome sequencing. One major system where this is becoming apparent is within the Genus Schistosoma, where schistosomiasis represents a disease of considerable medical and veterinary importance, the greatest burden of which occurs in sub-Saharan Africa. Interspecific hybridizations and introgressions bring an increased level of complexity over and above that already inherent within multihost, multiparasite systems, also representing an additional source of genetic variation that can drive evolution. This has the potential for profound implications for the control of parasitic diseases, including, but not exclusive to, widening host range, increased transmission potential and altered responses to drug therapy. Here, we present the challenging case example of haematobium group Schistosoma spp. hybrids in West Africa, a system involving multiple interacting parasites and multiple definitive hosts, in a region where zoonotic reservoirs of schistosomiasis were not previously considered to be of importance. We consider how existing mathematical model frameworks for schistosome transmission could be expanded and adapted to zoonotic hybrid systems, exploring how such model frameworks can utilize molecular and epidemiological data, as well as the complexities and challenges this presents. We also highlight the opportunities and value such mathematical models could bring to this and a range of similar multihost, multi and cross-hybridizing parasites systems in our changing world.
Crellen T, Walker M, Lamberton PH, et al., 2017, REDUCED EFFICACY OF PRAZIQUANTEL AGAINST SCHISTOSOMA MANSONI IS ASSOCIATED WITH MULTIPLE-ROUNDS OF MASS DRUG ADMINISTRATION: EPIDEMIOLOGICAL AND GENOMIC DATA FROM UGANDA, 65th Annual Meeting of the American-Society-of-Tropical-Medicine-and-Hygiene (ASTMH), Publisher: AMER SOC TROP MED & HYGIENE, Pages: 195-195, ISSN: 0002-9637
Deol AK, French MD, Walker M, et al., 2017, COMMUNITY-WIDE PATTERNS OF INFECTION AFTER MORE THAN TEN YEARS OF PREVENTIVE CHEMOTHERAPY FOR SCHISTOSOMIASIS AND SOIL-TRANSMITTED HELMINTH INFECTION IN UGANDA: ARE WE READY TO MOVE BEYOND MORBIDITY CONTROL?, 65th Annual Meeting of the American-Society-of-Tropical-Medicine-and-Hygiene (ASTMH), Publisher: AMER SOC TROP MED & HYGIENE, Pages: 558-558, ISSN: 0002-9637
Easton AV, Oliveira RG, Walker M, et al., 2017, Sources of variability in the measurement of Ascaris lumbricoides infection intensity by Kato-Katz and qPCR, PARASITES & VECTORS, Vol: 10, ISSN: 1756-3305
Gower CM, Gehre F, Marques SR, et al., 2017, Phenotypic and genotypic monitoring of Schistosoma mansoni in Tanzanian schoolchildren five years into a preventative chemotherapy national control programme, PARASITES & VECTORS, Vol: 10, ISSN: 1756-3305
Gower CM, Vince L, Webster JP, 2017, Should we be treating animal schistosomiasis in Africa? The need for a One Health economic evaluation of schistosomiasis control in people and their livestock, TRANSACTIONS OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE, Vol: 111, Pages: 244-247, ISSN: 0035-9203
Lamberton PHL, Faust CL, Webster JP, 2017, Praziquantel decreases fecundity in Schistosoma mansoni adult worms that survive treatment: evidence from a laboratory life-history trade-offs selection study, INFECTIOUS DISEASES OF POVERTY, Vol: 6, ISSN: 2049-9957
Leger E, Webster JP, 2017, Hybridizations within the Genus Schistosoma: implications for evolution, epidemiology and control., Parasitology, Vol: 144, Pages: 65-80
Hybridization of parasites is an emerging public health concern in our changing world. Hybridization and introgression in parasites and pathogens can have major impacts on the host and the epidemiology and evolution of disease. Schistosomiasis is a Neglected Tropical Disease of profound medical and veterinary importance across many parts of the world, with the greatest human burden within sub-Saharan Africa. Here we review how early phenotypic identification and recent confirmation through molecular studies on naturally occurring infections, combined with experimental manipulations, have revealed evidence of viable hybridization and introgressions within and between human and animal schistosome species. Environmental and anthropogenic changes in selective pressures following, for instance, new dam constructions, altered agricultural practices, together with mass drug administration programmes, may all be predicted to further impact the availability of suitable definitive and intermediate hosts for schistosomes. It is therefore imperative to understand the distribution and role of such novel zoonotic hybrid schistosomes on host range, drug efficacy, and hence ultimately transmission potential, if we are to achieve and maintain sustainable control.
Pitaksakulrat O, Kiatsopit N, Laoprom N, et al., 2017, Preliminary genetic evidence of two different populations of Opisthorchis viverrini in Lao PDR, PARASITOLOGY RESEARCH, Vol: 116, Pages: 1247-1256, ISSN: 0932-0113
Viana M, Faust CL, Haydon DT, et al., 2017, The effects of subcurative praziquantel treatment on life-history traits and trade-offs in drug-resistant Schistosoma mansoni, Evolutionary Applications, ISSN: 1752-4563
© 2017 John Wiley & Sons Ltd. Natural selection acts on all organisms, including parasites, to maximize reproductive fitness. Drug resistance traits are often associated with life-history costs in the absence of treatment. Schistosomiasis control programmes rely on mass drug administration to reduce human morbidity and mortality. Although hotspots of reduced drug efficacy have been reported, resistance is not widespread. Using Bayesian state-space models (SSMs) fitted to data from an in vivo laboratory system, we tested the hypothesis that the spread of resistant Schistosoma mansoni may be limited by life-history costs not present in susceptible counterparts. S. mansoni parasites from a praziquantel-susceptible (S), a praziquantel-resistant (R) or a mixed line of originally resistant and susceptible parasites (RS) were exposed to a range of praziquantel doses. Parasite numbers at each life stage were quantified in their molluscan intermediate and murine definitive hosts across four generations, and SSMs were used to estimate key life-history parameters for each experimental group over time. Model outputs illustrated that parasite adult survival and fecundity in the murine host decreased across all lines, including R, with increasing drug pressure. Trade-offs between adult survival and fecundity were observed in all untreated lines, and these remained strong in S with praziquantel pressure. In contrast, trade-offs between adult survival and fecundity were lost under praziquantel pressure in R. As expected, parasite life-history traits within the molluscan host were complex, but trade-offs were demonstrated between parasite establishment and cercarial output. The observed trade-offs between generations within hosts, which were modified by praziquantel treatment in the R line, could limit the spread of R parasites under praziquantel pressure. Whilst such complex life-history costs may be difficult to detect using standard empirical methods, we demonstrate th
Webster JP, Borlase A, Rudge JW, 2017, Who acquires infection from whom and how? Disentangling multi-host and multi-mode transmission dynamics in the 'elimination' era., Philos Trans R Soc Lond B Biol Sci, Vol: 372
Multi-host infectious agents challenge our abilities to understand, predict and manage disease dynamics. Within this, many infectious agents are also able to use, simultaneously or sequentially, multiple modes of transmission. Furthermore, the relative importance of different host species and modes can itself be dynamic, with potential for switches and shifts in host range and/or transmission mode in response to changing selective pressures, such as those imposed by disease control interventions. The epidemiology of such multi-host, multi-mode infectious agents thereby can involve a multi-faceted community of definitive and intermediate/secondary hosts or vectors, often together with infectious stages in the environment, all of which may represent potential targets, as well as specific challenges, particularly where disease elimination is proposed. Here, we explore, focusing on examples from both human and animal pathogen systems, why and how we should aim to disentangle and quantify the relative importance of multi-host multi-mode infectious agent transmission dynamics under contrasting conditions, and ultimately, how this can be used to help achieve efficient and effective disease control.This article is part of the themed issue 'Opening the black box: re-examining the ecology and evolution of parasite transmission'.
Crellen T, Allan F, David S, et al., 2016, Whole genome resequencing of the human parasite Schistosoma mansoni reveals population history and effects of selection, SCIENTIFIC REPORTS, Vol: 6, ISSN: 2045-2322
Crellen T, Walker M, Lamberton PHL, et al., 2016, Reduced Efficacy of Praziquantel Against Schistosoma mansoni Is Associated With Multiple Rounds of Mass Drug Administration, CLINICAL INFECTIOUS DISEASES, Vol: 63, Pages: 1151-1159, ISSN: 1058-4838
Deol A, Webster JP, Walker M, et al., 2016, Development and evaluation of a Markov model to predict changes in schistosomiasis prevalence in response to praziquantel treatment: a case study of Schistosoma mansoni in Uganda and Mali, PARASITES & VECTORS, Vol: 9, ISSN: 1756-3305
Easton AV, Oliveira RG, O'Connell EM, et al., 2016, Multi-parallel qPCR provides increased sensitivity and diagnostic breadth for gastrointestinal parasites of humans: field-based inferences on the impact of mass deworming, PARASITES & VECTORS, Vol: 9, ISSN: 1756-3305
Fleming FM, Matovu F, Hansen KS, et al., 2016, A mixed methods approach to evaluating community drug distributor performance in the control of neglected tropical diseases, PARASITES & VECTORS, Vol: 9, ISSN: 1756-3305
Léger E, Garba A, Hamidou AA, et al., 2016, Introgressed animal schistosomes schistosoma curassoni and S. Bovis naturally infecting humans, Emerging Infectious Diseases, Vol: 22, Pages: 2212-2214, ISSN: 1080-6040
Petney TN, Sithithaworn P, Andrews RH, et al., 2016, Foodborne trematodes: a diverse and challenging group of neglected parasites, TRANSACTIONS OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE, Vol: 110, Pages: 1-3, ISSN: 0035-9203
Webster JP, Gower CM, Knowles SCL, et al., 2016, One health - an ecological and evolutionary framework for tackling Neglected Zoonotic Diseases, EVOLUTIONARY APPLICATIONS, Vol: 9, Pages: 313-333, ISSN: 1752-4571
Webster JP, Lamberton PHL, McConkey GA, 2016, The Toxoplasma gondii Model of Schizophrenia, Handbook of Behavioral Neuroscience, Pages: 225-241
© 2016 Elsevier B.V. With increasing pressure to understand both acute and chronic diseases, renewed recognition of infectious causation is occurring. Epidemiological and neuropathological studies indicate that some cases of the neuropsychiatric disorder schizophrenia are associated with environmental factors, such as exposure to the protozoan Toxoplasma gondii. Reasons for this include, but are not exclusive to, T. gondii's ability to establish persistent infection within the central nervous system, to manipulate or alter host behavior, the occurrence of neurological and psychiatric symptoms in some infected individuals, and an association between infection with increased incidence of schizophrenia. Moreover, several of the medications used to treat schizophrenia have been demonstrated in vitro and in vivo to possess anti-T. gondii properties. We focus here on the potential role of T. gondii as an etiological agent and a model for some cases of schizophrenia and question what infection studies may elucidate in terms of the epidemiology, evolution, and clinical applications of these diseases.
Albonico M, Levecke B, LoVerde PT, et al., 2015, Monitoring the efficacy of drugs for neglected tropical diseases controlled by preventive chemotherapy, JOURNAL OF GLOBAL ANTIMICROBIAL RESISTANCE, Vol: 3, Pages: 229-236, ISSN: 2213-7165
Chevalier FD, LeClec'h W, LoVerde PT, et al., 2015, POPULATION "EXOMICS" OF SCHISTOSOMA MANSONI, Publisher: AMER SOC TROP MED & HYGIENE, Pages: 545-545, ISSN: 0002-9637
Deol AK, Webster JP, Harrison W, et al., 2015, Development of a Markov transition probability model to predict changes in schistosomiasis infection following treatment, TROPICAL MEDICINE & INTERNATIONAL HEALTH, Vol: 20, Pages: 237-237, ISSN: 1360-2276
Easton AV, Oliveira RG, O'Connell EM, et al., 2015, MULTI-PARALLEL QPCR PROVIDES INCREASED SENSITIVITY AND DIAGNOSTIC BREADTH ALLOWING FOR IMPROVED EVALUATION OF THE IMPACT OF DEWORMING PROGRAMS FOR SOIL-TRANSMITTED HELMINTHS (STH), Publisher: AMER SOC TROP MED & HYGIENE, Pages: 18-18, ISSN: 0002-9637
Fleming FM, Matovu F, Webster JP, et al., 2015, COMMUNITY DRUG DISTRIBUTOR PERFORMANCE IN THE CONTROL OF NEGLECTED TROPICAL DISEASES: ARE WE ASKING TOO MUCH?, Publisher: AMER SOC TROP MED & HYGIENE, Pages: 375-375, ISSN: 0002-9637
French MD, Churcher TS, Webster JP, et al., 2015, Estimation of changes in the force of infection for intestinal and urogenital schistosomiasis in countries with schistosomiasis control initiative-assisted programmes, PARASITES & VECTORS, Vol: 8, ISSN: 1756-3305
King KC, Stelkens RB, Webster JP, et al., 2015, Hybridization in Parasites: Consequences for Adaptive Evolution, Pathogenesis, and Public Health in a Changing World, PLOS PATHOGENS, Vol: 11, ISSN: 1553-7366
Knowles SCL, Webster BL, Garba A, et al., 2015, Epidemiological Interactions between Urogenital and Intestinal Human Schistosomiasis in the Context of Praziquantel Treatment across Three West African Countries, PLoS Neglected Tropical Diseases, Vol: 9, ISSN: 1935-2735
Lamberton PH, Mitchell K, Gower CM, et al., 2015, HOTSPOTS OF SCHISTOSOMA MANSONI TRANSMISSION TEN YEARS INTO A MASS DRUG ADMINISTRATION PROGRAM, Publisher: AMER SOC TROP MED & HYGIENE, Pages: 558-558, ISSN: 0002-9637
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