The Epidemiology of Filariasis Control

Michael, Edwin

doi:10.1007/0-306-47661-4_6

Cited by 14 publications

(14 citation statements)

References 23 publications

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“…This framework has allowed us to reveal for the first time evidence not only for the presence of density‐dependence in this filarial transmission process in each of the three major vector mosquito genera, but also for the existence of significant variation in the degree of such regulation between these vectors. These results represent significant new findings regarding filariasis transmission, and are thus of great value to our overall aim of gaining a better quantitative understanding of the population dynamics and control of this parasite (Chan et al ., 1998; Michael et al ., 1998; Norman et al ., 2000; Michael, 2002).…”

Section: Discussionmentioning

confidence: 99%

“…Gaining a quantitative understanding of parasite infection dynamics in the vector mosquito population is a key requirement to improving knowledge regarding the transmission, persistence and control of lymphatic filariasis (Bryan & Southgate, 1976; Dye, 1992; Wada et al ., 1994; Subramanian et al ., 1998; Michael, 2002). Despite this, and in spite of a significant body of work in this area (Samarawickrema et al ., 1985; Bryan & Southgate, 1988a,b; Bryan et al ., 1990; Southgate & Bryan, 1992; Subramanian et al ., 1998), the forms of the various components of the macroparasite‐vector infection process, including uptake of microfilaria (mf) from the human host, development of mf to the infective stage larvae (L3), and vector mortality rate, within (and between) the three major vector genera, i.e.…”

Section: Introductionmentioning

confidence: 99%

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Transmission dynamics of lymphatic filariasis: density‐dependence in the uptake ofWuchereria bancroftimicrofilariae by vector mosquitoes

Snow¹,

Michael²

2002

Medical Vet Entomology

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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 metaanalytical framework for synthesizing the observed regressions across studies, we show here for the first time clear evidence for the existence of densitydependence 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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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Transmission dynamics of lymphatic filariasis: density‐dependence in the uptake ofWuchereria bancroftimicrofilariae by vector mosquitoes

Snow¹,

Michael²

2002

Medical Vet Entomology

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“…Resolving the role of such residual microfilaraemia in maintaining transmission has now become a pressing research need, particularly in the context of the global initiative to control the disease by mass chemotherapy. Epidemiological work has shown that the key to successfully resolving this issue is better quantitative understanding of infection processes in the mosquito vectors, and in particular how density-dependent processes in larval development might act synergistically or antagonistically with the currently recommended methods of control ( Bryan & Southgate, 1976;Dye, 1992;Wada et al , 1994;Subramanian et al , 1998;Michael, 2002 ).…”

Section: Transmission Dynamics Of Lymphatic Filariasis: Vector-specifmentioning

confidence: 99%

“…The development of transmission dynamics models for filarial diseases ( Dietz, 1982;Chan et al , 1998;Basanez & Boussinesq, 1999;Norman et al , 2000;Michael, 2002;Michael et al , 2004 ) means that quantitative tools are now available to study the complex relationships between human, parasite and vector populations, and to clarify how density-dependent factors in both the host and vector populations may contribute to observed population dynamics as well as the control of infection. One constraint of current models, however, is that parasite infection dynamics in the vector host are based on only one form of the functional relationship describing the mf to L3 development process ( Plaisier et al , 1998;Norman et al , 2000 ).…”

Section: Transmission Dynamics Of Lymphatic Filariasis: Vector-specifmentioning

confidence: 99%

Transmission dynamics of lymphatic filariasis: vector‐specific density dependence in the development ofWuchereria bancroftiinfective larvae in mosquitoes

Snow

Bockarie

Michael

2006

Medical Vet Entomology

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The principles of meta-analysis developed in a previous study were extended to investigate the process of Wuchereria bancrofti (Cobbold) (Filarioidea: Onchocercidae) infection in mosquito (Diptera: Culicidae) hosts, focusing specifically on the functional forms and strength of density dependence in the development of ingested microfilariae (mf) to infective (third instar) larvae (L3). Mathematical models describing observed mf-L3 functional responses for each of the major three parasite-transmitting vector genera, Aedes, Culex and Anopheles mosquitoes, were fitted to paired mf-L3 data collated from all available studies in the published literature. Model parameters were estimated and compared by deriving and applying a data synthetic framework, based on applying a non-linear weighted regression model for fitting mathematical models to multistudy data. The results confirm previous findings of the existence of significant between-genera differences in the mf-L3 development relationship, particularly with regard to the occurrence of limitation in Culex mosquitoes and facilitation in Aedes and Anopheles mosquitoes. New and unexpected findings regarding L3 development from ingested mf were discovered as follows: (1) for Culex, overcompensation in L3 development at higher intensities of mf (or a peaked mf-L3 functional response) was detected; (2) for Aedes mosquitoes, facilitation (with an apparent asymptotic constraint on L3 development at high mf densities) was shown to be the major process governing L3 development, and (3) for Anopheles, a stronger facilitation type of response with no apparent saturation in L3 development appears to govern L3 output from ingested mf. These results yield major new insights regarding filarial vector infection dynamics and their potential impacts on parasite control, and demonstrate the efficacy of employing a data synthetic approach to reveal and estimate parasitic infection processes in host populations.

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“…An understanding of LF transmission dynamics is crucial for the implementation and monitoring of elimination programmes91011121314. Mathematical models are being used to guide decision making on the best strategies to eliminate lymphatic filariasis15.…”

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confidence: 99%

Filarial infection influences mosquito behaviour and fecundity

Gleave

Cook

Taylor

et al. 2016

Sci Rep

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Understanding vector-parasite interactions is increasingly important as we move towards the endpoint goals set by the Global Programme for the Elimination of Lymphatic Filariasis (GPELF), as interaction dynamics may change with reduced transmission pressure. Elimination models used to predict programmatic endpoints include parameters for vector-specific transmission dynamics, despite the fact that our knowledge of the host-seeking behaviour of filariasis infected mosquitoes is lacking. We observed a dynamic, stage-specific and density dependent change in Aedes aegypti behaviour towards host cues when exposed to Brugia malayi filarial parasites. Infected mosquitoes exhibited reduced activation and flight towards a host during the period of larval development (L1/L2), transitioning to a 5 fold increase in activation and flight towards a host when infective stage larvae (L3) were present (p < 0.001). In uninfected control mosquitoes, we observed a reduction in convergence towards a host during the same period. Furthermore, this behaviour was density dependent with non-activated mosquitoes harbouring a greater burden of L1 and L2 larvae while activated mosquitoes harboured a greater number of L3 (p < 0.001). Reductions in fecundity were also density-dependent, and extended to mosquitoes that were exposed to microfilariae but did not support larval development.

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The Epidemiology of Filariasis Control

Cited by 14 publications

References 23 publications

Transmission dynamics of lymphatic filariasis: density‐dependence in the uptake ofWuchereria bancroftimicrofilariae by vector mosquitoes

Transmission dynamics of lymphatic filariasis: density‐dependence in the uptake ofWuchereria bancroftimicrofilariae by vector mosquitoes

Transmission dynamics of lymphatic filariasis: vector‐specific density dependence in the development ofWuchereria bancroftiinfective larvae in mosquitoes

Filarial infection influences mosquito behaviour and fecundity

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