Re-Visiting Trichuris trichiura Intensity Thresholds Based on Anemia during Pregnancy

Theresa W Gyorkos,Martín Casapía,Nicolas L Gilbert,Antonio Montresor,Renée Larocque,Charles H King

doi:10.1371/journal.pntd.0001783

Abstract

BackgroundThe intensity categories, or thresholds, currently used for Trichuris trichiura (ie. epg intensities of 1–999 (light); 1,000–9,999 epg (moderate), and ≥10,000 epg (heavy)) were developed in the 1980s, when there were little epidemiological data available on dose-response relationships. This study was undertaken to determine a threshold for T. trichiura-associated anemia in pregnant women and to describe the implications of this threshold in terms of the need for primary prevention and chemotherapeutic interventions.Methodology/Principal FindingsIn Iquitos, Peru, 935 pregnant women were tested for T. trichiura infection in their second trimester of pregnancy; were given daily iron supplements throughout their pregnancy; and had their blood hemoglobin levels measured in their third trimester of pregnancy. Women in the highest two T. trichiura intensity quintiles (601–1632 epg and ≥1633 epg) had significantly lower mean hemoglobin concentrations than the lowest quintile (0–24 epg). They also had a statistically significantly higher risk of anemia, with adjusted odds ratios of 1.67 (95% CI: 1.02, 2.62) and 1.73 (95% CI: 1.09, 2.74), respectively.Conclusions/SignificanceThis analysis provides support for categorizing a T. trichiura infection ≥1,000 epg as ‘moderate’, as currently defined by the World Health Organization. Because this ‘moderate’ level of T. trichiura infection was found to be a significant risk factor for anemia in pregnant women, the intensity of Trichuris infection deemed to cause or aggravate anemia should no longer be restricted to the ‘heavy’ intensity category. It should now include both ‘heavy’ and ‘moderate’ intensities of Trichuris infection. Evidence-based deworming strategies targeting pregnant women or populations where anemia is of concern should be updated accordingly.

Highlights

The most recent comprehensive estimation of the prevalences of the soil-transmitted helminthiases (STH) documents a global prevalence of 17% for Trichuris trichiura infection, with approximately 800 million persons infected at any one time [1,2]
In 1987, an expert committee convened by the World Health organization (WHO) established infection intensity categories for STH, including T. trichiura, in order to inform the management of large-scale deworming programs [11]
Among the 935 pregnant women included in the analysis, 82% were infected with Trichuris trichiura, and 43% were co-infected with T. trichiura and hookworms

Summary

Introduction

The most recent comprehensive estimation of the prevalences of the soil-transmitted helminthiases (STH) documents a global prevalence of 17% for Trichuris trichiura infection, with approximately 800 million persons infected at any one time [1,2]. In 1987, an expert committee convened by the World Health organization (WHO) established infection intensity categories for STH, including T. trichiura, in order to inform the management of large-scale deworming programs [11]. T. trichiura infection was defined as light (1–999 epg) or heavy (.10,000 epg) [11]. These categories were based primarily on expert opinion and little doseresponse data from the field, and were described as ‘‘arbitrary’’ by this committee. This study was undertaken to determine a threshold for T. trichiura-associated anemia in pregnant women and to describe the implications of this threshold in terms of the need for primary prevention and chemotherapeutic interventions

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