Publications
272 results found
Bottomley C, Isham V, Vivas-Martínez S, et al., 2017, Response to the Letter to the Editor by Eberhard et al., Parasites & Vectors, Vol: 10, ISSN: 1756-3305
In a Letter to the Editor, Eberhard et al. question the validity of our model of skin snip sensitivity and argue against the use of skin snips to evaluate onchocerciasis elimination by mass drug administration. Here we discuss their arguments and compare model predictions with observed data to assess the validity of our model.
Sahimin N, Lim YAL, Ariffin F, et al., 2017, Socio-demographic determinants of Toxoplasma gondii seroprevalence in migrant workers of Peninsular Malaysia, Parasites & Vectors, Vol: 10, ISSN: 1756-3305
BackgroundThe number of migrants working in Malaysia has increased sharply since the 1970’s and there is concern that infectious diseases endemic in other (e.g. neighbouring) countries may be inadvertently imported. Compulsory medical screening prior to entering the workforce does not include parasitic infections such as toxoplasmosis. Therefore, this study aimed to evaluate the seroprevalence of T. gondii infection among migrant workers in Peninsular Malaysia by means of serosurveys conducted on a voluntary basis among low-skilled and semi-skilled workers from five working sectors, namely, manufacturing, food service, agriculture and plantation, construction and domestic work.MethodsA total of 484 migrant workers originating from rural locations in neighbouring countries, namely, Indonesia (n = 247, 51.0%), Nepal (n = 99, 20.5%), Bangladesh (n = 72, 14.9%), India (n = 52, 10.7%) and Myanmar (n = 14, 2.9%) were included in this study.ResultsThe overall seroprevalence of T. gondii was 57.4% (n = 278; 95% CI: 52.7–61.8%) with 52.9% (n = 256; 95% CI: 48.4–57.2%) seropositive for anti-Toxoplasma IgG only, 0.8% (n = 4; 95% CI: 0.2–1.7%) seropositive for anti-Toxoplasma IgM only and 3.7% (n = 18; 95% CI: 2.1–5.4%) seropositive with both IgG and IgM antibodies. All positive samples with both IgG and IgM antibodies showed high avidity (> 40%), suggesting latent infection. Age (being older than 45 years), Nepalese nationality, manufacturing occupation, and being a newcomer in Malaysia (excepting domestic work) were positively and statistically significantly associated with seroprevalence (P < 0.05).ConclusionsThe results of this study suggest that better promotion of knowledge about parasite transmission is required for both migrant workers and permanent residents in Malaysia. Efforts should be made to
Basanez M, 2017, The Genomic Architecture of Novel Simulium damnosum WolbachiaProphage Sequence Elements and Implications for OnchocerciasisEpidemiology, Frontiers in Microbiology, ISSN: 1664-302X
Walker M, Stolk WA, Dixon MA, et al., 2017, Modelling the elimination of river blindness using long-term epidemiological and programmatic data from Mali and Senegal, Epidemics, Vol: 18, Pages: 4-15, ISSN: 1755-4365
The onchocerciasis transmission models EPIONCHO and ONCHOSIM have been independently developedand used to explore the feasibility of eliminating onchocerciasis from Africa with mass (annual orbiannual) distribution of ivermectin within the timeframes proposed by the World Health Organization(WHO) and endorsed by the 2012 London Declaration on Neglected Tropical Diseases (i.e. by 2020/2025).Based on the findings of our previous model comparison, we implemented technical refinements andtested the projections of EPIONCHO and ONCHOSIM against long-term epidemiological data from twoWest African transmission foci in Mali and Senegal where the observed prevalence of infection wasbrought to zero circa 2007–2009 after 15–17 years of mass ivermectin treatment. We simulated theseinterventions using programmatic information on the frequency and coverage of mass treatments andtrained the model projections using longitudinal parasitological data from 27 communities, evaluatingthe projected outcome of elimination (local parasite extinction) or resurgence. We found that EPIONCHOand ONCHOSIM captured adequately the epidemiological trends during mass treatment but that resurgence,while never predicted by ONCHOSIM, was predicted by EPIONCHO in some communities with thehighest (inferred) vector biting rates and associated pre-intervention endemicities. Resurgence can beextremely protracted such that low (microfilarial) prevalence between 1% and 5% can be maintained for3–5 years before manifesting more prominently. We highlight that post-treatment and post-eliminationsurveillance protocols must be implemented for long enough and with high enough sensitivity to detectpossible residual latent infections potentially indicative of resurgence. We also discuss uncertainty anddifferences between EPIONCHO and ONCHOSIM projections, the potential importance of vector controlin high-transmission settings as a complementary intervention strategy, and the short remaining timelinefo
Winskill P, Harrison W, French M, et al., 2017, Assessing the impact of intervention strategies against Taenia solium cysticercosis using the EPICYST transmission model, Parasites & Vectors, Vol: 10, ISSN: 1756-3305
BackgroundThe pork tapeworm, Taenia solium, and associated human infections, taeniasis, cysticercosis and neurocysticercosis, are serious public health problems, especially in developing countries. The World Health Organization (WHO) has set goals for having a validated strategy for control and elimination of T. solium taeniasis/cysticercosis by 2015 and interventions scaled-up in selected countries by 2020. Timely achievement of these internationally-endorsed targets requires that the relative benefits and effectiveness of potential interventions be explored rigorously within a quantitative framework.MethodsA deterministic, compartmental transmission model (EPICYST) was developed to capture the dynamics of the taeniasis/cysticercosis disease system in the human and pig hosts. Cysticercosis prevalence in humans, an outcome of high epidemiological and clinical importance, was explicitly modelled. A next generation matrix approach was used to derive an expression for the basic reproduction number, R 0. A full sensitivity analysis was performed using a methodology based on Latin-hypercube sampling partial rank correlation coefficient index.ResultsEPICYST outputs indicate that chemotherapeutic intervention targeted at humans or pigs would be highly effective at reducing taeniasis and cysticercosis prevalence when applied singly, with annual chemotherapy of humans and pigs resulting, respectively, in 94 and 74% of human cysticercosis cases averted. Improved sanitation, meat inspection and animal husbandry are less effective but are still able to reduce prevalence singly or in combination. The value of R 0 for taeniasis was estimated at 1.4 (95% Credible Interval: 0.5–3.6).ConclusionsHuman- and pig-targeted drug-focussed interventions appear to be the most efficacious approach from the options currently available. The model presented is a forward step towards developing an informed control and elimination strategy for cysticercosis. Together with its validation agai
Cucunubá ZM, Manne-Goehler JM, Diaz D, et al., 2017, How universal is coverage and access to diagnosis and treatment for Chagas disease in Colombia? A health systems analysis, Social science & medicine, Vol: 175, Pages: 187-198, ISSN: 0037-7856
Limited access to Chagas disease diagnosis and treatment is a major obstacle to reaching the 2020 World Health Organization milestones of delivering care to all infected and illpatients. Colombia has been identified as a health system in transition, reporting one of the highest levels of health insurance coverage in Latin America. We explore if and how this high level of coverage extends to those with Chagas disease, a traditionally marginalised population. Using a mixed methods approach, we calculate coverage for screening, diagnosis and treatment of Chagas. We then identify supply-side constraints both quantitatively and qualitatively. A review of official registries of tests and treatments for Chagas disease delivered between 2008 and 2014 is compared to estimates of infected people. Using the Flagship Framework, we explore barriers limiting access to care. Screening coverage is estimated at 1.2% of the population at risk. Aetiological treatment with either benznidazol or nifurtimox covered 0.3–0.4% of the infected population. Barriers to accessing screening, diagnosis and treatment are identified for each of the Flagship Framework’s five dimensions of interest: financing, payment, regulation, organisation and persuasion. The main challenges identified were: a lack of clarity in terms of financial responsibilities in a segmented health system, claims of limited resources for undertaking activities particularly in primary care, non-inclusion of confirmatory test(s) in the basic package of diagnosis and care, poor logistics in the distribution and supply chain of medicines, and lack of awareness of medical personnel. Very low screening coverage emerges as a key obstacle hindering access to care for Chagas disease. Findings suggest serious shortcomings in this health system for Chagas disease, despite the success of universal health insurance scale-up in Colombia. Whether these shortcomings exist in relation to other neglected tropical diseases need
Milton P, Walker M, Kuesel AC, et al., 2017, MODELLING ALTERNATIVE STRATEGIES FOR ONCHOCERCIASIS ELIMINATION: THE CASE FOR MOXIDECTIN, 66th Annual Meeting of the American-Society-of-Tropical-Medicine-and-Hygiene (ASTMH), Publisher: AMER SOC TROP MED & HYGIENE, Pages: 559-560, ISSN: 0002-9637
- Author Web Link
- Cite
- Citations: 1
Frempong KK, Walker M, Cheke RA, et al., 2017, RESPONSES OF <i>ONCHOCERCA VOLVULUS</i> AFTER THE INTRODUCTION OF BIANNUAL TREATMENT WITH IVERMECTIN IN GHANA, 66th Annual Meeting of the American-Society-of-Tropical-Medicine-and-Hygiene (ASTMH), Publisher: AMER SOC TROP MED & HYGIENE, Pages: 561-561, ISSN: 0002-9637
Routledge I, Walker M, Cheke RA, et al., 2017, MATHEMATICAL MODELLING OF FOCAL VECTOR CONTROL AS A COMPLEMENTARY STRATEGY FOR ONCHOCERCIASIS ELIMINATION, 66th Annual Meeting of the American-Society-of-Tropical-Medicine-and-Hygiene (ASTMH), Publisher: AMER SOC TROP MED & HYGIENE, Pages: 7-7, ISSN: 0002-9637
- Author Web Link
- Cite
- Citations: 2
McCulloch K, McCaw J, McVernon J, et al., 2017, INVESTIGATION INTO THE EFFECT OF HOST MIGRATION ON THE TRANSMISSION OF <i>ONCHOCERCA VOLVULUS</i> USING A PATCH MODEL, 66th Annual Meeting of the American-Society-of-Tropical-Medicine-and-Hygiene (ASTMH), Publisher: AMER SOC TROP MED & HYGIENE, Pages: 564-564, ISSN: 0002-9637
Walker M, Milton P, Monnot F, et al., 2017, DESIGNING ANTIFILARIAL DRUG TRIALS USING CLINICAL TRIAL SIMULATORS, 66th Annual Meeting of the American-Society-of-Tropical-Medicine-and-Hygiene (ASTMH), Publisher: AMER SOC TROP MED & HYGIENE, Pages: 165-166, ISSN: 0002-9637
Colebunders R, Mandro M, Njamnshi AK, et al., 2017, REPORT OF THE FIRST INTERNATIONAL WORKSHOP ON ONCHOCERCIASIS-ASSOCIATED EPILEPSY: A CHALLENGE TO THE SCIENTIFIC AND MEDICAL COMMUNITIES AND A RESEARCH AGENDA GOING FORWARDS, 66th Annual Meeting of the American-Society-of-Tropical-Medicine-and-Hygiene (ASTMH), Publisher: AMER SOC TROP MED & HYGIENE, Pages: 163-163, ISSN: 0002-9637
Deol AK, 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
Background: Understanding whether schistosomiasis control programmes are on course to control morbidityand potentially switch towards elimination interventions would benefit from user-friendly quantitative tools thatfacilitate analysis of progress and highlight areas not responding to treatment. This study aimed to develop andevaluate such a tool using large datasets collected during Schistosomiasis Control Initiative-supported controlprogrammes.Methods: A discrete-time Markov model was developed using transition probability matrices parameterized withcontrol programme longitudinal data on Schistosoma mansoni obtained from Uganda and Mali. Four matrix variants(A-D) were used to compare different data types for parameterization: A-C from Uganda and D from Mali. Matrix Aused data at baseline and year 1 of the control programme; B used year 1 and year 2; C used baseline and year 1from selected districts, and D used baseline and year 1 Mali data. Model predictions were tested against 3 subsetsof the Uganda dataset: dataset 1, the full 4-year longitudinal cohort; dataset 2, from districts not used toparameterize matrix C; dataset 3, cross-sectional data, and dataset 4, from Mali as an independent dataset.Results: The model parameterized using matrices A, B and D predicted similar infection dynamics (overall andwhen stratified by infection intensity). Matrices A-D successfully predicted prevalence in each follow-up year for lowand high intensity categories in dataset 1 followed by dataset 2. Matrices A, B and D yielded similar and closematches to dataset 1 with marginal discrepancies when comparing model outputs against datasets 2 and 3. MatrixC produced more variable results, correctly estimating fewer data points.Conclusion: Model outputs closely matched observed values and were a useful predictor of the infection dynamicsof S. mansoni when using longitudinal and cross-sectional data from Uganda. This also held when the model wastested with data from Mali. This was most
Basanez MG, Walker M, Turner HC, et al., 2016, River Blindness: Mathematical Models for Control and Elimination, ADVANCES IN PARASITOLOGY, VOL 94: MATHEMATICAL MODELS FOR NEGLECTED TROPICAL DISEASES: ESSENTIAL TOOLS FOR CONTROL AND ELIMINATION, PT B, Vol: 94, Pages: 247-341, ISSN: 0065-308X
Ortu G, Assoum M, Wittmann U, et al., 2016, The impact of an 8-year mass drug administration programme on prevalence, intensity and co-infections of soil-transmitted helminthiases in Burundi, Parasites & Vectors, Vol: 9, Pages: 513-513, ISSN: 1756-3305
BACKGROUND: Soil-transmitted helminth (STH) infections are amongst the most prevalent infections in the world. Mass drug administration (MDA) programmes have become the most commonly used national interventions for endemic countries to achieve elimination. This paper aims to describe the effect of an 8-year MDA programme on the prevalence, intensity of infection and co-infection of STH in Burundi from 2007 to 2014 and critically appraise the trajectory towards STH elimination in the country. RESULTS: Annual STH parasitological surveys (specifically, a "pilot study" from 2007 to 2011, an "extension study" from 2008 to 2011, and a "national reassessment" in 2014; n = 27,658 children), showed a significant drop in prevalence of infection with any STH ("pooled STH") between baseline and 2011 in both studies, falling from 32 to 16 % in the pilot study, and from 35 to 16 % in the extension study. Most STH infections were of low intensity according to WHO classification. The national reassessment in 2014 showed that prevalence of pooled STH remained significantly below the prevalence in 2007 in both studies but there was no further decrease in STH prevalence from 2011 levels during this time. Spatial dependence analysis showed that prevalence of Trichuris trichiura and Ascaris lumbricoides had a tendency to cluster over the years, whilst only trends in spatial dependence were evident for hookworm infections. Spatial dependence fluctuated over the course of the programme for Ascaris lumbricoides and Trichuris trichiura. However, spatial trends in spatial dependence were evident in 2010 for Ascaris lumbricoides. Analysis of spatial clustering of intensity of infection and heavy infections revealed that the intensity changed over time for all parasites. Heavy intensity was only evident in Ascaris lumbricoides for 2008 and did not appear in proceeding years and other parasites. CONCLUSIONS: These results demonstra
Pinsent A, Blake IM, Basáñez MG, et al., 2016, Mathematical Modelling of Trachoma Transmission, Control and Elimination., Publisher: Elsevier, Pages: 1-48
The World Health Organization has targeted the elimination of blinding trachoma by the year 2020. To this end, the Global Elimination of Blinding Trachoma (GET, 2020) alliance relies on a four-pronged approach, known as the SAFE strategy (S for trichiasis surgery; A for antibiotic treatment; F for facial cleanliness and E for environmental improvement). Well-constructed and parameterized mathematical models provide useful tools that can be used in policy making and forecasting in order to help to control trachoma and understand the feasibility of this large-scale elimination effort. As we approach this goal, the need to understand the transmission dynamics of infection within areas of different endemicities, to optimize available resources and to identify which strategies are the most cost-effective becomes more pressing. In this study, we conducted a review of the modelling literature for trachoma and identified 23 articles that included a mechanistic or statistical model of the transmission, dynamics and/or control of (ocular) Chlamydia trachomatis. Insights into the dynamics of trachoma transmission have been generated through both deterministic and stochastic models. A large body of the modelling work conducted to date has shown that, to varying degrees of effectiveness, antibiotic administration can reduce or interrupt trachoma transmission. However, very little analysis has been conducted to consider the effect of nonpharmaceutical interventions (and particularly the F and E components of the SAFE strategy) in helping to reduce transmission. Furthermore, very few of the models identified in the literature review included a structure that permitted tracking of the prevalence of active disease (in the absence of active infection) and the subsequent progression to disease sequelae (the morbidity associated with trachoma and ultimately the target of GET 2020 goals). This represents a critical gap in the current trachoma modelling literature, which m
Basanez M, Lamberton PHL, Cheke RA, et al., 2016, Onchocerciasis transmission in Ghana: the human blood index of sibling species of the Simulium damnosum complex, Parasites & Vectors, Vol: 9, ISSN: 1756-3305
BackgroundVector-biting behaviour is important for vector-borne disease (VBD) epidemiology. The proportion of blood meals taken on humans (the human blood index, HBI), is a component of the biting rate per vector on humans in VBD transmission models. Humans are the definitive host of Onchocerca volvulus, but the simuliid vectors feed on a range of animals and HBI is a key indicator of the potential for human onchocerciasis transmission. Ghana has a diversity of Simulium damnosum complex members, which are likely to vary in their HBIs, an important consideration for parameterization of onchocerciasis control and elimination models.MethodsHost-seeking and ovipositing S. damnosum (sensu lato) (s.l.) were collected from seven villages in four Ghanaian regions. Taxa were morphologically and molecularly identified. Blood meals from individually stored blackfly abdomens were used for DNA profiling, to identify previous host choice. Household, domestic animal, wild mammal and bird surveys were performed to estimate the density and diversity of potential blood hosts of blackflies.ResultsA total of 11,107 abdomens of simuliid females (which would have obtained blood meal(s) previously) were tested, with blood meals successfully amplified in 3,772 (34 %). A single-host species was identified in 2,857 (75.7 %) of the blood meals, of which 2,162 (75.7 %) were human. Simulium soubrense Beffa form, S. squamosum C and S. sanctipauli Pra form were the most anthropophagic (HBI = 0.92, 0.86 and 0.70, respectively); S. squamosum E, S. yahense and S. damnosum (sensu stricto) (s.s.)/S. sirbanum were the most zoophagic (HBI = 0.44, 0.53 and 0.63, respectively). The degree of anthropophagy decreased (but not statistically significantly) with increasing ratio of non-human/human blood hosts. Vector to human ratios ranged from 139 to 1,198 blackflies/person.ConclusionsDNA profiling can successfully identify blood meals from host-seeking and ovipositing blackflies.
Ferguson NM, Cucunubá ZM, Dorigatti I, et al., 2016, Countering the Zika epidemic in Latin America, Science, Vol: 353, Pages: 353-354, ISSN: 1095-9203
Bottomley C, Isham V, Vivas-Martínez S, et al., 2016, Modelling Neglected Tropical Diseases diagnostics: the sensitivity of skin snips for Onchocerca volvulus in near elimination and surveillance settings, Parasites & Vectors, Vol: 9, ISSN: 1756-3305
BACKGROUND: The African Programme for Onchocerciasis Control has proposed provisional thresholds for the prevalence of microfilariae in humans and of L3 larvae in blackflies, below which mass drug administration (MDA) with ivermectin can be stopped and surveillance started. Skin snips are currently the gold standard test for detecting patent Onchocerca volvulus infection, and the World Health Organization recommends their use to monitor progress of treatment programmes (but not to verify elimination). However, if they are used (in transition and in parallel to Ov-16 serology), sampling protocols should be designed to demonstrate that programmatic goals have been reached. The sensitivity of skin snips is key to the design of such protocols. METHODS: We develop a mathematical model for the number of microfilariae in a skin snip and parameterise it using data from Guatemala, Venezuela, Ghana and Cameroon collected before the start of ivermectin treatment programmes. We use the model to estimate sensitivity as a function of time since last treatment, number of snips taken, microfilarial aggregation and female worm fertility after exposure to 10 annual rounds of ivermectin treatment. RESULTS: The sensitivity of the skin snip method increases with time after treatment, with most of the increase occurring between 0 and 5 years. One year after the last treatment, the sensitivity of two skin snips taken from an individual infected with a single fertile female worm is 31 % if there is no permanent effect of multiple ivermectin treatments on fertility; 18 % if there is a 7 % reduction per treatment, and 0.6 % if there is a 35 % reduction. At 5 years, the corresponding sensitivities are 76 %, 62 % and 4.7 %. The sensitivity improves significantly if 4 skin snips are taken: in the absence of a permanent effect of ivermectin, the sensitivity of 4 skin snips is 53 % 1 year and 94 % 5 years after the last treatme
Frempong KK, Walker M, Cheke RA, et al., 2016, Does increasing treatment frequency address suboptimal responses to ivermectin for the control and elimination of river blindness?, Clinical Infectious Diseases, Vol: 62, Pages: 1338-1347, ISSN: 1537-6591
Background. Several African countries have adopted a biannual ivermectin distribution strategy in some foci to control and eliminate onchocerciasis. In 2010, the Ghana Health Service started biannual distribution to combat transmission hotspots and suboptimal responses to treatment. We assessed the epidemiological impact of the first 3 years of this strategy and quantified responses to ivermectin over 2 consecutive rounds of treatment in 10 sentinel communities.Methods. We evaluated Onchocerca volvulus community microfilarial intensity and prevalence in persons aged ≥20 years before the first, second, and fifth (or sixth) biannual treatment rounds using skin snip data from 956 participants. We used longitudinal regression modeling to estimate rates of microfilarial repopulation of the skin in a cohort of 217 participants who were followed up over the first 2 rounds of biannual treatment.Results. Biannual treatment has had a positive impact, with substantial reductions in infection intensity after 4 or 5 rounds in most communities. We identified 3 communities—all having been previously recognized as responding suboptimally to ivermectin—with statistically significantly high microfilarial repopulation rates. We did not find any clear association between microfilarial repopulation rate and the number of years of prior intervention, coverage, or the community level of infection.Conclusions. The strategy of biannual ivermectin treatment in Ghana has reduced O. volvulus microfilarial intensity and prevalence, but suboptimal responses to treatment remain evident in a number of previously and consistently implicated communities. Whether increasing the frequency of treatment will be sufficient to meet the World Health Organization's 2020 elimination goals remains uncertain.
Botto C, Basanez MG, Escalona M, et al., 2016, Evidence of suppression of onchocerciasis transmission in the Venezuelan Amazonian focus., Parasites & Vectors, Vol: 9, ISSN: 1756-3305
BACKGROUND: The World Health Organization (WHO) has set goals for onchocerciasis elimination in Latin America by 2015. Most of the six previously endemic countries are attaining this goal by implementing twice a year (and in some foci, quarterly) mass ivermectin (Mectizan®) distribution. Elimination of transmission has been verified in Colombia, Ecuador and Mexico. Challenges remain in the Amazonian focus straddling Venezuela and Brazil, where the disease affects the hard-to-reach Yanomami indigenous population. We provide evidence of suppression of Onchocerca volvulus transmission by Simulium guianense s.l. in 16 previously hyperendemic Yanomami communities in southern Venezuela after 15 years of 6-monthly and 5 years of 3-monthly mass ivermectin treatment. METHODS: Baseline and monitoring and evaluation parasitological, ophthalmological, entomological and serological surveys were conducted in selected sentinel and extra-sentinel communities of the focus throughout the implementation of the programme. RESULTS: From 2010 to 2012-2015, clinico-parasitological surveys indicate a substantial decrease in skin microfilarial prevalence and intensity of infection; accompanied by no evidence (or very low prevalence and intensity) of ocular microfilariae in the examined population. Of a total of 51,341 S. guianense flies tested by PCR none had L3 infection (heads only). Prevalence of infective flies and seasonal transmission potentials in 2012-2013 were, respectively, under 1 % and 20 L3/person/transmission season. Serology in children aged 1-10 years demonstrated that although 26 out of 396 (7 %) individuals still had Ov-16 antibodies, only 4/218 (2 %) seropositives were aged 1-5 years. CONCLUSIONS: We report evidence of recent transmission and morbidity suppression in some communities of the focus representing 75 % of the Yanomami population and 70 % of all known communities. We conclude that onchocerciasis transmission co
Cucunubá ZM, Okuwoga O, Basanez MG, et al., 2016, Increased mortality attributed to Chagas disease: a systematic review and meta-analysis., Parasites & Vectors, Vol: 9, ISSN: 1756-3305
BACKGROUND: The clinical outcomes associated with Chagas disease remain poorly understood. In addition to the burden of morbidity, the burden of mortality due to Trypanosoma cruzi infection can be substantial, yet its quantification has eluded rigorous scrutiny. This is partly due to considerable heterogeneity between studies, which can influence the resulting estimates. There is a pressing need for accurate estimates of mortality due to Chagas disease that can be used to improve mathematical modelling, burden of disease evaluations, and cost-effectiveness studies. METHODS: A systematic literature review was conducted to select observational studies comparing mortality in populations with and without a diagnosis of Chagas disease using the PubMed, MEDLINE, EMBASE, Web of Science and LILACS databases, without restrictions on language or date of publication. The primary outcome of interest was mortality (as all-cause mortality, sudden cardiac death, heart transplant or cardiovascular deaths). Data were analysed using a random-effects model to obtain the relative risk (RR) of mortality, the attributable risk percent (ARP), and the annual mortality rates (AMR). The statistic I(2) (proportion of variance in the meta-analysis due to study heterogeneity) was calculated. Sensitivity analyses and publication bias test were also conducted. RESULTS: Twenty five studies were selected for quantitative analysis, providing data on 10,638 patients, 53,346 patient-years of follow-up, and 2739 events. Pooled estimates revealed that Chagas disease patients have significantly higher AMR compared with non-Chagas disease patients (0.18 versus 0.10; RR = 1.74, 95 % CI 1.49-2.03). Substantial heterogeneity was found among studies (I(2) = 67.3 %). The ARP above background mortality was 42.5 %. Through a sub-analysis patients were classified by clinical group (severe, moderate, asymptomatic). While RR did not differ significantly betw
Walker M, Mabud T, Olliaro PL, et al., 2016, New approaches to measuring anthelminthic drug efficacy: parasitological responses of childhood schistosome infections to treatment with praziquantel, Parasites & Vectors, Vol: 9, ISSN: 1756-3305
BACKGROUND:By 2020, the global health community aims to control and eliminate human helminthiases, including schistosomiasis in selected African countries, principally by preventive chemotherapy (PCT) through mass drug administration (MDA) of anthelminthics. Quantitative monitoring of anthelminthic responses is crucial for promptly detecting changes in efficacy, potentially indicative of emerging drug resistance. Statistical models offer a powerful means to delineate and compare efficacy among individuals, among groups of individuals and among populations.METHODS:We illustrate a variety of statistical frameworks that offer different levels of inference by analysing data from nine previous studies on egg counts collected from African children before and after administration of praziquantel.RESULTS:We quantify responses to praziquantel as egg reduction rates (ERRs), using different frameworks to estimate ERRs among population strata, as average responses, and within strata, as individual responses. We compare our model-based average ERRs to corresponding model-free estimates, using as reference the World Health Organization (WHO) 90 % threshold of optimal efficacy. We estimate distributions of individual responses and summarize the variation among these responses as the fraction of ERRs falling below the WHO threshold.CONCLUSIONS:Generic models for evaluating responses to anthelminthics deepen our understanding of variation among populations, sub-populations and individuals. We discuss the future application of statistical modelling approaches for monitoring and evaluation of PCT programmes targeting human helminthiases in the context of the WHO 2020 control and elimination goals.
O'Hanlon SJ, Slater HC, Cheke R, et al., 2016, Model-Based Geostatistical Mapping of the Prevalence of Onchocerca volvulus in West Africa, PLOS Neglected Tropical Diseases, Vol: 10, ISSN: 1935-2735
Background. The initial endemicity (pre-control prevalence) of onchocerciasis has been shown to be an important determinant of the feasibility of elimination by mass ivermectin distribution. We present the first geostatistical map of microfilarial prevalence in the former Onchocerciasis Control Programme in West Africa (OCP) before commencement of antivectorial and antiparasitic interventions.Methods and Findings. Pre-control microfilarial prevalence data from 737 villages across the 11 constituent countries in the OCP epidemiological database were used as ground-truth data. These 737 data points, plus a set of statistically selected environmental covariates, were used in a Bayesian model-based geostatistical (B-MBG) approach to generate a continuous surface (at pixel resolution of 5 km x 5km) of microfilarial prevalence in West Africa prior to the commencement of the OCP. Uncertainty in model predictions was measured using a suite of validation statistics, performed on bootstrap samples of held-out validation data. The mean Pearson’s correlation between observed and estimated prevalence at validation locations was 0.693; the mean prediction error (average difference between observed and estimated values) was 0.77%, and the mean absolute prediction error (average magnitude of difference between observed and estimated values) was 12.2%. Within OCP boundaries, 17.8 million people were deemed to have been at risk, 7.55 million to have been infected, and mean microfilarial prevalence to have been 45% (range: 2–90%) in 1975.Conclusions and Significance. This is the first map of initial onchocerciasis prevalence in West Africa using B-MBG. Important environmental predictors of infection prevalence were identified and used in a model out-performing those without spatial random effects or environmental covariates. Results may be compared with recent epidemiological mapping efforts to find areas of persisting transmission. These methods may be extended to areas w
Basanez M-G, Anderson RM, 2016, ADVANCES IN PARASITOLOGY Mathematical Models for Neglected Tropical Diseases: Essential Tools for Control and Elimination, Part B PREFACE, Publisher: ELSEVIER ACADEMIC PRESS INC
Gambhir M, Grassly NC, Burton MJ, et al., 2015, Estimating the Future Impact of a Multi-Pronged Intervention Strategy on Ocular Disease Sequelae Caused by Trachoma: A Modeling Study, Ophthalmic Epidemiology, Vol: 22, Pages: 394-402, ISSN: 1744-5086
Purpose: Trachoma control programs are underway in endemic regions worldwide. They are based on the SAFE strategy (Surgery for trichiasis, Antibiotic distribution, Facial cleanliness, and Environmental improvement). Although much is known about the effect of community-wide treatment with antibiotics on the prevalence of Chlamydia trachomatis, the impact of the SAFE strategy on severe ocular disease sequelae (the main focus of the Global Elimination of blinding Trachoma by 2020 program) remains largely unknown.Methods: We use a mathematical model to explore the impact of each of the components of the SAFE strategy, individually and together, on disease sequelae, arising from repeat infection and subsequent conjunctival scarring. We ask whether two elimination goals, to reduce the prevalence of trachomatous trichiasis to 1 per 1000 persons, and the incidence of corneal opacity to 1 per 10,000 persons per annum, are achievable, and which combinations of interventions have the greatest impact on these indicators.Results: In high prevalence communities (here, >20% infection of children aged 1–9 years), a combination of efforts is needed to bring down sustainably the prevalence and incidence of ocular disease sequelae.Conclusion: The mass delivery of antibiotics is highly beneficial for the clearance of infection, inflammation and prevention of subsequent scarring, but needs to be supplemented with sustained reductions in transmission and surgery to consider realistically the elimination of blindness by the year 2020.
Hollingsworth TD, Adams ER, Anderson RM, et al., 2015, Quantitative analyses and modelling to support achievement of the 2020 goals for nine neglected tropical diseases, Parasites & Vectors, Vol: 8, ISSN: 1756-3305
Quantitative analysis and mathematical models are useful tools in informing strategies to control or eliminatedisease. Currently, there is an urgent need to develop these tools to inform policy to achieve the 2020 goals forneglected tropical diseases (NTDs). In this paper we give an overview of a collection of novel model-based analyseswhich aim to address key questions on the dynamics of transmission and control of nine NTDs: Chagas disease,visceral leishmaniasis, human African trypanosomiasis, leprosy, soil-transmitted helminths, schistosomiasis, lymphaticfilariasis, onchocerciasis and trachoma. Several common themes resonate throughout these analyses, including: theimportance of epidemiological setting on the success of interventions; targeting groups who are at highest risk ofinfection or re-infection; and reaching populations who are not accessing interventions and may act as a reservoirfor infection,. The results also highlight the challenge of maintaining elimination ‘as a public health problem’ whentrue elimination is not reached. The models elucidate the factors that may be contributing most to persistence ofdisease and discuss the requirements for eventually achieving true elimination, if that is possible. Overall thiscollection presents new analyses to inform current control initiatives. These papers form a base from which furtherdevelopment of the models and more rigorous validation against a variety of datasets can help to give moredetailed advice. At the moment, the models’ predictions are being considered as the world prepares for a finalpush towards control or elimination of neglected tropical diseases by 2020.
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
- Author Web Link
- Open Access Link
- Cite
- Citations: 14
Stolk WA, Walker M, Coffeng LE, et al., 2015, Required duration of mass ivermectin treatment for onchocerciasis elimination in Africa: a comparative modelling analysis, PARASITES & VECTORS, Vol: 8, ISSN: 1756-3305
- Author Web Link
- Open Access Link
- Cite
- Citations: 82
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.