EPIFIL: The development of an age-structured model for describing the transmission dynamics and control of lymphatic filariasis

Abstract

SUMMARYMathematical models of transmission dynamics of infectious diseases provide a useful tool for investigating the impact of community based control measures. Previously, we used a dynamic (constant force-of-infection) model for lymphatic filariasis to describe observed patterns of infection and disease in endemic communities. In this paper, we expand the model to examine the effects of control options against filariasis by incorporating the impact of age structure of the human community and by addressing explicitly the dynamics of parasite transmission from and to the vector population. This model is tested using data for Wuchereria bancrofti transmitted by Culex quinquefasciatus in Pondicherry, South India. The results show that chemotherapy has a larger short-term impact than vector control but that the effects of vector control can last beyond the treatment period. In addition we compare rates of recrudescence for drugs with different macrofilaricidal effects.

Mass Treatment to Eliminate Filariasis in Papua New Guinea

“…Evaluation of changes in filarial ecology after the cessation of mass treatment in Papua New Guinea and other areas of endemic infection will provide this information and can be used to validate and refine mathematical models designed to predict the threshold necessary to achieve eradication. 7,8,44,45 Supported by funds from the World Health Organization (F30/181/67) and the Papua New Guinea Institute of Medical Research. The data analysis was supported by a grant (U19 AI33061) from the Public Health Service.…”

“…[4][5][6] The threshold below which transmission will be interrupted is not known, but mathematical models that assume the reproductive life span of Wuchereria bancrofti is approximately five years predict that annual mass treatment for four to six years will be required. 7,8 In 1994 we initiated a trial comparing the efficacy of diethylcarbamazine plus ivermectin with that of diethylcarbamazine alone in limiting the transmission of filariasis in Papua New Guinea. The proportion of persons who were positive for microfilariae decreased by 76 to 99 percent, and the transmission potentialthe estimated number of infective (third-stage) larvae inoculated per person per year -decreased by 31 to 58 percent 12 months after a single dose of the drugs.…”

Transmission intensity and the patterns of Onchocerca volvulus infection in human communities.

“…1,7 Because there is insufficient evidence to date in support of the operation of density-dependent constraints upon worm fecundity and survival, we will assume that the main mechanism regulating parasite population abundance acts through limiting parasite establishment. 54,55 Our conjecture is that the proportion of L3 larvae developing into adult worms, ␦ H , is dependent on the intensity of exposure to L3 larvae as measured by the ATP. A functional relationship between ␦ H and ATP from Dietz 9 has consequently been modified as follows,…”

Continental-Scale, Data-Driven Predictive Assessment of Eliminating the Vector-Borne Disease, Lymphatic Filariasis, in Sub-Saharan Africa by 2020

“…These discrepancies in the results between studies highlight the importance of carefully considering the methodologies and threshold targets used by various workers in deriving intervention duration estimates. Thus, while the GPELF estimates are simply based on assuming that 5 years of annual MDA will be sufficient to break transmission in all areas, the latter results were based on predictions of a deterministic model [12,51,68,69] calibrated to a limited set of expected baseline prevalences within countries and which assumed an 85% MDA coverage and a target threshold of 1% mf for all areas. This use of uniform values for various intervention parameters, a weaker constraining of models to match only overall human infection data, plus the limited consideration of spatial heterogeneity in site-specific transmission dynamics clearly underlie the finding that 6-15 rounds of annual MDA would be sufficient to eliminate LF transmission in that work, compared to the significantly longer time periods we estimate here for the same 1% mf threshold (10-24 annual rounds between countries, depending on within-country heterogeneity in baseline mf prevalence and actual MDA/VC coverages and roll-out patterns achieved (Table 4)).…”