Understanding the relationship between prevalence of microfilariae and antigenaemia using a model of lymphatic filariasis infection.

Michael A. Irvine,Simon J. Brooker,Sammy M. Njenga,Claire Njeri Wamae,Jorge Cano,Shamini Gunawardena,T. Deirdre Hollingsworth

doi:10.1093/trstmh/trv096

Abstract

BackgroundLymphatic filariasis is a debilitating neglected tropical disease that affects impoverished communities. Rapid diagnostic tests of antigenaemia are a practical alternative to parasitological tests of microfilaraemia for mapping and surveillance. However the relationship between these two methods of measuring burden has previously been difficult to interpret.MethodsA statistical model of the distribution of worm burden and microfilariae (mf) and resulting antigenaemic and mf prevalence was developed and fitted to surveys of two contrasting sentinel sites undergoing interventions. The fitted model was then used to explore the relationship in various pre- and post-intervention scenarios.ResultsThe model had good quantitative agreement with the data and provided estimates of the reduction in mf output due to treatment. When extrapolating the results to a range of prevalences there was good qualitative agreement with published data.ConclusionsThe observed relationship between antigenamic and mf prevalence is a natural consequence of the relationship between prevalence and intensity of adult worms and mf production. The method described here allows the estimation of key epidemiological parameters and consequently gives insight into the efficacy of an intervention programme.

Highlights

Lymphatic filariasis (LF) is a debilitating disease caused by parasitic infection of the lymph nodes.[1]
The main idea is to construct the distribution of worm load in the population and the probability distribution of mf for an individual with a given worm load and use these to calculate the prevalence of antigenaemia and microfilaraemia in the population
We have shown using minimal assumptions of worm and mf distribution an explanation for the disparity between microfilaraemia and antigenaemia

Summary

Introduction

Lymphatic filariasis (LF) is a debilitating disease caused by parasitic infection of the lymph nodes.[1] most cases displayed are asymptomatic, prolonged and high burden can lead to abnormal enlargement of body parts causing pain, severe disability and social stigma. Mf counts are a good tool for estimating the prevalence of infection, and the mean mf load and infectious pool in a community.[3] Microfilariae are counted in blood samples through either a blood smear or a counting chamber and require expert parasitologists to detect. Sensitivity and specificity of the test are 97% and 100% respectively, this is dependent upon mf load, blood volume and parasitological method.[4,5]. Lymphatic filariasis is a debilitating neglected tropical disease that affects impoverished communities. The relationship between these two methods of measuring burden has previously been difficult to interpret

Methods

Results

Discussion

Conclusion