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Stephano MA, Mayengo MM, Irunde JI, Kuznetsov D. Sensitivity analysis and parameters estimation for the transmission of lymphatic filariasis. Heliyon 2023; 9:e20066. [PMID: 37810166 PMCID: PMC10559806 DOI: 10.1016/j.heliyon.2023.e20066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Revised: 08/28/2023] [Accepted: 09/10/2023] [Indexed: 10/10/2023] Open
Abstract
Lymphatic filariasis is a neglected tropical disease which poses public health concern and socio-economic challenges in developing and low-income countries. In this paper, we formulate a deterministic mathematical model for transmission dynamics of lymphatic filariasis to generate data by white noise and use least square method to estimate parameter values. The validity of estimated parameter values is tested by Gaussian distribution method. The residuals of model outputs are normally distributed and hence can be used to study the dynamics of Lymphatic filariasis. After deriving the basic reproduction number, R 0 by the next generation matrix approach, the Partial Rank Correlation Coefficient is employed to explore which parameters significantly affect and most influential to the model outputs. The analysis for equilibrium states shows that the Lymphatic free equilibrium is globally asymptotically stable when the basic reproduction number is less a unity and endemic equilibrium is globally asymptotically stable when R 0 ≥ 1 . The findings reveal that rate of human infection, recruitment rate of mosquitoes increase the average new infections for Lymphatic filariasis. Moreover, asymptomatic individuals contribute significantly in the transmission of Lymphatic filariasis.
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Affiliation(s)
- Mussa A. Stephano
- School of Computation and Communication Science and Engineering, The Nelson Mandela African Institution of Science and Technology (NM-AIST), P.O.BOX 447 Arusha, Tanzania
- Mkwawa University College of Education, Department of Mathematics, Physics and Informatics, P.O.Box 2513, Iringa, Tanzania
| | - Maranya M. Mayengo
- School of Computation and Communication Science and Engineering, The Nelson Mandela African Institution of Science and Technology (NM-AIST), P.O.BOX 447 Arusha, Tanzania
| | - Jacob I. Irunde
- Mkwawa University College of Education, Department of Mathematics, Physics and Informatics, P.O.Box 2513, Iringa, Tanzania
| | - Dmitry Kuznetsov
- School of Computation and Communication Science and Engineering, The Nelson Mandela African Institution of Science and Technology (NM-AIST), P.O.BOX 447 Arusha, Tanzania
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2
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Cheng Y, Wang X, Pan Q, He M. Modeling the Parasitic Filariasis Spread by Mosquito in Periodic Environment. COMPUTATIONAL AND MATHEMATICAL METHODS IN MEDICINE 2017; 2017:4567452. [PMID: 28280518 PMCID: PMC5320389 DOI: 10.1155/2017/4567452] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Accepted: 11/24/2016] [Indexed: 11/17/2022]
Abstract
In this paper a mosquito-borne parasitic infection model in periodic environment is considered. Threshold parameter R0 is given by linear next infection operator, which determined the dynamic behaviors of system. We obtain that when R0 < 1, the disease-free periodic solution is globally asymptotically stable and when R0 > 1 by Poincaré map we obtain that disease is uniformly persistent. Numerical simulations support the results and sensitivity analysis shows effects of parameters on R0, which provided references to seek optimal measures to control the transmission of lymphatic filariasis.
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Affiliation(s)
- Yan Cheng
- School of Mathematics, Taiyuan University of Technology, Taiyuan 030024, China
| | - Xiaoyun Wang
- School of Mathematics, Taiyuan University of Technology, Taiyuan 030024, China
| | - Qiuhui Pan
- School of Innovation Experiment, Dalian University of Technology, Dalian 116024, China
| | - Mingfeng He
- School of Innovation Experiment, Dalian University of Technology, Dalian 116024, China
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3
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Drovandi CC, Pettitt AN, Lee A. Bayesian Indirect Inference Using a Parametric Auxiliary Model. Stat Sci 2015. [DOI: 10.1214/14-sts498] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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4
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Kennedy DA, Dukic V, Dwyer G. Pathogen growth in insect hosts: inferring the importance of different mechanisms using stochastic models and response-time data. Am Nat 2014; 184:407-23. [PMID: 25141148 PMCID: PMC10495239 DOI: 10.1086/677308] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Pathogen population dynamics within individual hosts can alter disease epidemics and pathogen evolution, but our understanding of the mechanisms driving within-host dynamics is weak. Mathematical models have provided useful insights, but existing models have only rarely been subjected to rigorous tests, and their reliability is therefore open to question. Most models assume that initial pathogen population sizes are so large that stochastic effects due to small population sizes, so-called demographic stochasticity, are negligible, but whether this assumption is reasonable is unknown. Most models also assume that the dynamic effects of a host's immune system strongly affect pathogen incubation times or "response times," but whether such effects are important in real host-pathogen interactions is likewise unknown. Here we use data for a baculovirus of the gypsy moth to test models of within-host pathogen growth. By using Bayesian statistical techniques and formal model-selection procedures, we are able to show that the response time of the gypsy moth virus is strongly affected by both demographic stochasticity and a dynamic response of the host immune system. Our results imply that not all response-time variability can be explained by host and pathogen variability, and that immune system responses to infection may have important effects on population-level disease dynamics.
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Affiliation(s)
- David A. Kennedy
- Department of Ecology and Evolution, University of Chicago, Chicago, Illinois 60637
- Center for Infectious Disease Dynamics, Pennsylvania State University, University Park, Pennsylvania 16802
- Fogarty International Center, National Institutes of Health, Bethesda, Maryland 20892
| | - Vanja Dukic
- Department of Applied Mathematics, University of Colorado, Boulder, Colorado 80305
| | - Greg Dwyer
- Department of Ecology and Evolution, University of Chicago, Chicago, Illinois 60637
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5
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Drovandi CC, Pettitt AN. Bayesian experimental design for models with intractable likelihoods. Biometrics 2013; 69:937-48. [PMID: 24131221 DOI: 10.1111/biom.12081] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2013] [Revised: 06/01/2013] [Accepted: 06/01/2013] [Indexed: 11/28/2022]
Abstract
In this paper we present a methodology for designing experiments for efficiently estimating the parameters of models with computationally intractable likelihoods. The approach combines a commonly used methodology for robust experimental design, based on Markov chain Monte Carlo sampling, with approximate Bayesian computation (ABC) to ensure that no likelihood evaluations are required. The utility function considered for precise parameter estimation is based upon the precision of the ABC posterior distribution, which we form efficiently via the ABC rejection algorithm based on pre-computed model simulations. Our focus is on stochastic models and, in particular, we investigate the methodology for Markov process models of epidemics and macroparasite population evolution. The macroparasite example involves a multivariate process and we assess the loss of information from not observing all variables.
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Affiliation(s)
- Christopher C Drovandi
- School of Mathematical Sciences, Queensland University of Technology, Brisbane, Queensland, Australia
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6
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Drovandi CC, Pettitt AN, Faddy MJ. Approximate Bayesian computation using indirect inference. J R Stat Soc Ser C Appl Stat 2011. [DOI: 10.1111/j.1467-9876.2010.00747.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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7
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Schwab AE, Churcher TS, Schwab AJ, Basáñez MG, Prichard RK. Population genetics of concurrent selection with albendazole and ivermectin or diethylcarbamazine on the possible spread of albendazole resistance in Wuchereria bancrofti. Parasitology 2006; 133:589-601. [PMID: 16834821 DOI: 10.1017/s003118200600076x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2006] [Revised: 05/23/2006] [Accepted: 05/24/2006] [Indexed: 11/07/2022]
Abstract
The Global Program for the Elimination of Lymphatic Filariasis (GPELF) intends to achieve its aims through yearly mass treatments with albendazole (ABZ) combined with ivermectin (IVM) or diethylcarbamazine (DEC). The use of ABZ and IVM separately to combat parasites of veterinary importance has, on many occasions, resulted in widespread drug resistance. In order to help predict the spread of potential ABZ resistance alleles through a population of Wuchereria bancrofti, we have developed a mathematical model that incorporates population genetics into EPIFIL, a model which examines the transmission dynamics of the parasite. Our model considers the effect of the combined treatments on the frequency of a recessive allele, which confers ABZ resistance. The model predicts that after 10 yearly treatments with ALB and DEC, 85% coverage and an initial resistance allele frequency of 5%, the frequency of the resistance genotype will increase from 0.25 to 12.7%. If non-random mating is assumed, the initial genotype frequency will be 2.34% and will increase to 62.7%. ABZ and IVM combination treatment may lead to weaker selection for this genotype. Treatment coverage, initial allele frequencies and number of treatments also affect the rate of selection.
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Affiliation(s)
- A E Schwab
- Institute of Parasitology, McGill University, 21111 Lakeshore Road, Ste-Anne-de-Bellevue, Quebec, Canada, H9X 3V9
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8
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Naish S, McCarthy J, Williams GM. Prevalence, intensity and risk factors for soil-transmitted helminth infection in a South Indian fishing village. Acta Trop 2004; 91:177-87. [PMID: 15234667 DOI: 10.1016/j.actatropica.2004.04.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2004] [Revised: 04/22/2004] [Accepted: 04/30/2004] [Indexed: 10/26/2022]
Abstract
A study of the prevalence, intensity and risk factors for soil-transmitted helminth infection was undertaken among school children aged 5-9 years attending a primary school in the fishing village in Peda Jalaripet, Visakhapatnam, South India. One hundred and eighty nine (92.6%) of 204 children were infected with one or more soil transmitted helminth parasites. The predominant parasite was Ascaris lumbricoides (prevalence of 91%), followed by Trichuris trichiura (72%) and hookworm (54%). Study of age-specific prevalence and intensity of infection revealed that the prevalence and intensity of A. lumbricoides infection was higher among younger children than older children. While aggregation of parasite infection was observed, hookworm infection was more highly aggregated than either A. lumbricoides or T. trichiura. Multivariate analysis identified parental occupation, child's age and mother's education as the potential risk factors contributing to the high intensity of A. lumbricoides infection. Children from fishing families with low levels of education of the mother had the highest intensity of A. lumbricoides infection. As the outcome of chemotherapy programs to control soil transmitted helminth infection is dependant on the dynamics of their transmission, there is a need for further studies to better define the role of specific factors that determine their prevalence, intensity and aggregation in different epidemiological settings.
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Affiliation(s)
- S Naish
- Queensland Institute of Medical Research, The University of Queensland, Herston Road, Brisbane, Qld 4029, Australia
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9
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Subramanian S, Stolk WA, Ramaiah KD, Plaisier AP, Krishnamoorthy K, Van Oortmarssen GJ, Dominic Amalraj D, Habbema JDF, Das PK. The dynamics ofWuchereria bancroftiinfection: a model-based analysis of longitudinal data from Pondicherry, India. Parasitology 2004; 128:467-82. [PMID: 15180315 DOI: 10.1017/s0031182004004822] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
This paper presents a model-based analysis of longitudinal data describing the impact of integrated vector management on the intensity ofWuchereria bancroftiinfection in Pondicherry, India. The aims of this analysis were (1) to gain insight into the dynamics of infection, with emphasis on the possible role of immunity, and (2) to develop a model that can be used to predict the effects of control. Using the LYMFASIM computer simulation program, two models with different types of immunity (anti-L3 larvae or anti-adult worm fecundity) were compared with a model without immunity. Parameters were estimated by fitting the models to data from 5071 individuals with microfilaria-density measurement before and after cessation of a 5-year vector management programme. A good fit, in particular of the convex shape of the age-prevalence curve, required inclusion of anti-L3 or anti-fecundity immunity in the model. An individual's immune-responsiveness was found to halve in ~10 years after cessation of boosting. Explanation of the large variation in Mf-density required considerable variation between individuals in exposure and immune responsiveness. The mean life-span of the parasite was estimated at about 10 years. For the post-control period, the models predict a further decline in Mf prevalence, which agrees well with observations made 3 and 6 years after cessation of the integrated vector management programme.
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Affiliation(s)
- S Subramanian
- Vector Control Research Centre (Indian Council of Medical Research), Indira Nagar, Medical Complex, Pondicherry-605 006, India.
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10
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Riley S, Donnelly CA, Ferguson NM. Robust parameter estimation techniques for stochastic within-host macroparasite models. J Theor Biol 2003; 225:419-30. [PMID: 14615200 DOI: 10.1016/s0022-5193(03)00266-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We present a stochastic model of the within-host population dynamics of lymphatic filariasis, and use a simulated goodness-of-fit (GOF) method to estimate immunological parameters and their confidence intervals from experimental data. A variety of deterministic moment closure approximations to the stochastic system are explored and compared with simulation results. For the maximum GOF parameter estimates, none of the methods of closure accurately reproduce the behaviour of the stochastic model. However, direct analysis of the stochastic model demonstrates that the high levels of variation observed in the data can be reproduced without requiring parameters to vary between hosts. This indicates that the observed aggregation of parasite load may be dynamically generated by random variation in the development of an effective immune response against parasite larvae.
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Affiliation(s)
- Steven Riley
- Department of Infectious Disease Epidemiology, Imperial College London, St. Mary's Campus, Norfolk Place, W2 1PG London, UK.
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11
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Cornell SJ, Isham VS, Smith G, Grenfell BT. Spatial parasite transmission, drug resistance, and the spread of rare genes. Proc Natl Acad Sci U S A 2003; 100:7401-5. [PMID: 12771377 PMCID: PMC165887 DOI: 10.1073/pnas.0832206100] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2002] [Indexed: 11/18/2022] Open
Abstract
The transmission of many parasitic worms involves aggregated movement between hosts of "packets" of infectious larvae. We use a generic metapopulation model to show that this aggregation naturally promotes the preferential spread of rare recessive genes, compared with the expectations of traditional nonspatial models. A more biologically realistic model also demonstrates that this effect could explain the rapid observed spread of recessive or weakly dominant drug-resistant genotypes in nematode parasites of sheep. This promotion of a recessive trait arises from a novel mechanism of inbreeding arising from the metapopulation dynamics of transmission.
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Affiliation(s)
- S J Cornell
- Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, United Kingdom.
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12
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Abstract
Empirical studies of helminth parasites reveal that the distribution of parasite burdens in their host populations is highly aggregated. This aggregation is fundamental to the ecology and epidemiology of helminth parasites. Results from a stochastic model predict that aggregation of helminth parasites is inversely related to the intensity of host immunity. Aggregation also decreases with antigenic heterogeneity and increases with heterogeneity in transmissibility among parasite strains. It is also found that the degree of aggregation is greater when immunity affects parasite fecundity than when immunity acts on host susceptibility. Potential relevance of this result for assessing the influence of vaccines that target either host susceptibility or parasite fecundity on the level of aggregation and consequent effects on drug resistance and disease prevalence are discussed.
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Affiliation(s)
- Alison P Galvani
- Department of Integrative Biology, University of California, Berkeley, California 94720, USA.
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13
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Snow LC, Michael E. Transmission dynamics of lymphatic filariasis: density-dependence in the uptake of Wuchereria bancrofti microfilariae by vector mosquitoes. MEDICAL AND VETERINARY ENTOMOLOGY 2002; 16:409-423. [PMID: 12510894 DOI: 10.1046/j.1365-2915.2002.00396.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Gaining a better understanding of parasite infection dynamics in the vector mosquito (Diptera: Culicidae) population is central to improving knowledge regarding the transmission, persistence and hence control of lymphatic filariasis. Here, we use data on mosquito feeding experiments collated from the published literature to examine the available evidence regarding the functional form of the first component of this parasite-vector relationship for Wuchereria bancrofti (Filarioidea: Onchocercidae) causing Bancroftian filariasis, i.e. the rate of microfilariae (mf) uptake from the blood of infected humans by the feeding mosquito vector. Using a simple logarithmic regression model for describing the observed relationships between the mean numbers of mf ingested per mosquito and parasite load in humans in each study, and a linear mixed-effects meta-analytical framework for synthesizing the observed regressions across studies, we show here for the first time clear evidence for the existence of density-dependence in this process for all the three major filariasis transmitting mosquito vectors. An important finding of this study is that this regulation of mf uptake also varies significantly between the vector genera, being weakest in Culex, comparatively stronger in Aedes and most severe and occurring at significantly lower human mf loads in Anopheles mosquitoes. The analysis of the corresponding mf uptake prevalence data has further highlighted how density-dependence in mf uptake may influence the observed distributions of mf in vector populations. These results show that whereas strong regulation of mf uptake, especially when it leads to saturation in uptake at low human parasite intensities, can lead to static distributions of mf per mosquito with host parasite intensity, a weaker regulation of mf ingestion can give rise to changes in both mean mf loads and in the frequency distribution of parasites/mosquito with increasing human parasite intensity. These findings highlight the importance of considering local vector infection dynamics when attempting to predict the impacts of community-based filariasis control. They also emphasize the value of developing and applying robust meta-analytic methods for estimating functional relationships regarding parasitic infection from population ecological data.
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Affiliation(s)
- L C Snow
- Department of Infectious Disease Epidemiology, Faculty of Medicine, Imperial College of Science Technology and Medicine, University of London, UK.
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Basáñez MG, Ricárdez-Esquinca J. Models for the population biology and control of human onchocerciasis. Trends Parasitol 2001; 17:430-8. [PMID: 11530355 DOI: 10.1016/s1471-4922(01)02013-x] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The absence of animal models in which to reproduce successfully the complete life cycle of Onchocerca volvulus has hindered progress towards unravelling the processes involved in the regulation of parasite abundance in the vertebrate host. Mathematical frameworks have been developed to explore the consequences of such processes in determining parasite population dynamics and the effect on these of control interventions. Post-control predictions are strongly influenced by the assumptions concerning the reproductive life span of the adult female worm (the longest-lived parasite stage) and the distribution of its survival times, and this notion is important to all frameworks. Here, we review the development of models concerning onchocerciasis and discuss the various approaches that have been used, presenting a deterministic framework with parameter values estimated from the Mexican onchocerciasis control programme. This model is used to evaluate interventions combining the removal of adult worms (nodulectomy) and the microfilaricidal and possibly sterilizing effect of ivermectin.
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Affiliation(s)
- M G Basáñez
- Dept of Infectious Disease Epidemiology, Imperial College School of Medicine (St. Mary's campus), Norfolk Place, W2 1PG., London, UK.
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15
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Michael E, Simonsen PE, Malecela M, Jaoko WG, Pedersen EM, Mukoko D, Rwegoshora RT, Meyrowitsch DW. Transmission intensity and the immunoepidemiology of bancroftian filariasis in East Africa. Parasite Immunol 2001; 23:373-88. [PMID: 11472557 DOI: 10.1046/j.1365-3024.2001.00398.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Previous attempts to determine the interactions between filariasis transmission intensity, infection and chronic disease have been limited by a lack of a theoretical framework that allows the explicit examination of mechanisms that may link these variables at the community level. Here, we show how deterministic mathematical models, in conjunction with analyses of standardized field data from communities with varying parasite transmission intensities, can provide a particularly powerful framework for investigating this topic. These models were based on adult worm population dynamics, worm initiated chronic disease and two major forms of acquired immunity (larval- versus adult-worm generated) explicitly linked to community transmission intensity as measured by the Annual Transmission Potential (ATP). They were then fitted to data from low, moderate and moderately high transmission communities from East Africa to determine the mechanistic relationships between transmission, infection and observed filarial morbidity. The results indicate a profound effect of transmission intensity on patent infection and chronic disease, and on the generation and impact of immunity on these variables. For infection, the analysis indicates that in areas of higher parasite transmission, community-specific microfilarial rates may increase proportionately with transmission intensity until moderated by the generation of herd immunity. This supports recent suggestions that acquired immunity in filariasis is transmission driven and may be significant only in areas of high transmission. In East Africa, this transmission threshold is likely to be higher than an ATP of at least 100. A new finding from the analysis of the disease data is that per capita worm pathogenicity could increase with transmission intensity such that the prevalences of both hydrocele and lymphoedema, even without immunopathological involvement, may increase disproportionately with transmission intensity. For lymphoedema, this rise may be further accelerated with the onset of immunopathology. An intriguing finding is that there may be at least two types of immunity operating in filariasis: one implicated in anti-infection immunity and generated by past experience of adult worms, the other involved in immune-mediated pathology and based on cumulative experience of infective larvae. If confirmed, these findings have important implications for the new global initiative to achieve control of this disease.
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Affiliation(s)
- E Michael
- Department of Infectious Disease Epidemiology, Imperial College School of Medicine, London, UK
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Needham C, Kim HT, Hoa NV, Cong LD, Michael E, Drake L, Hall A, Bundy DA. Epidemiology of soil-transmitted nematode infections in Ha Nam Province, Vietnam. Trop Med Int Health 1998; 3:904-12. [PMID: 9855404 DOI: 10.1046/j.1365-3156.1998.00324.x] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Baseline epidemiological data are presented from a parasitological survey conducted in Thuy Loi commune, Ha Nam province, Vietnam; a farming community where night soil is routinely used as fertilizer for crops. 177 households were visited and 543 individuals (aged 1-88 years) recruited to the study. Helminth infection intensity was assessed by Kato-Katz to determine the density of parasite eggs per gram of stool (epg). Ascaris lumbricoides, Trichuris trichiura and hookworm infections were the only species detected. 83% of individuals were infected with A. lumbricoides (mean epg = 11,971), 94% with T. trichiura (mean epg = 793) and 59% with hookworm (mean epg = 302). Age-dependent patterns of infection prevalence and intensity were similar for A. lumbricoides and T. trichiura, but markedly different for hookworm infection. Similarly, age-dependency in the k-values for the three infections was due to covariance with the respective mean intensities with age rather than to independent age effects, with similar patterns for A. lumbricoides and T. trichiura, and a different pattern for hookworm. Three major conclusions can be drawn from the multiple-species analyses: There is positive interaction between A. lumbricoides and T. trichiura infections; high-intensity A. lumbricoides infections are significantly associated with high-intensity T. trichiura infections; and there is positive interaction between these two species such that infection intensity of A. lumbricoides is higher in individuals with concurrent T. trichiura infection than in individuals without and vice versa.
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Affiliation(s)
- C Needham
- Wellcome Trust Centre for the Epidemiology of Infectious Disease, University of Oxford, UK
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