Schistosoma, other helminth infections, and associated risk factors in preschool-aged children in urban Tanzania

Khadija Said,Marcel Tanner,Upendo Mwingira,Karim Manji,Jerry Hella,Neema Shija,Francis Mhimbira,Lukas Fenner,Jürg Utzinger,Fatma Aziz,Anna M Mandalakas,Stefanie Knopp,Christian Schindler,Tatu Nassoro,Jennifer A Downs

doi:10.1371/journal.pntd.0006017

Abstract

BackgroundDespite the high prevalence of helminth infections among preschool-aged children, control programs in sub-Saharan countries primarily focus on school-aged populations. We assessed the prevalence of helminth infections and determined risk factors for infection among preschool-aged children in the urban setting of Dar es Salaam, Tanzania.MethodologyStarting in October 2015, we conducted a 12-month prospective study among tuberculosis (TB)-exposed children under the age of 5 years and unexposed controls from neighboring households. At the time of recruitment, we collected medical histories, assessed development and cognitive functions, and performed medical examinations. We performed full blood cell counts and screened for HIV and malaria. Point-of-care circulating cathodic antigen (POC-CCA), urine filtration, Kato-Katz, FLOTAC, and Baermann tests were employed to detect helminth infections in urine and stool. Helminth infections were stratified for Schistosoma and other helminths to identify risk factors, using logistic regression.Principal findingsWe included 310 children with a median age of 26 months (inter quartile range 17–42 months) in the study. Among these, 189 were TB-exposed and 121 TB-unexposed. Two thirds of the children were anemic (hemoglobin level <11 g/dl) and the HIV prevalence was 1.3%. Schistosoma spp. was the predominant helminth species (15.8%; 95% confidence interval [CI] 12.1–20.3%). Other helminth infections were less frequent (9.0%, 95% CI 6.3–12.8%). Poor hygiene, use of household water sources, and TB-exposure were not associated with helminth infection. Development and cognitive scores did not significantly differ in helminth-infected and uninfected peers, but hemoglobin levels were significantly lower in helminth-infected children (10.1 g/dl vs. 10.4 g/dl, p = 0.027).Conclusions/significanceIn Dar es Salaam, a city with more than 4 million inhabitants, the prevalence of Schistosoma spp. infection among preschool-aged children was unexpectedly high. Setting-specific interventions that target preschool-aged children and urban settlements should be considered to reduce the transmission of Schistosoma and other helminth infections and to improve children’s health.

Highlights

Helminth infections affect more than 1.5 billion people globally and are common amongst economically deprived populations [1, 2]
Among 310 included children, we found that one in six children was infected with the blood fluke Schistosoma, while one in 11 children were infected with soil-transmitted helminths
Anemia was found among 65% of children, among those infected with parasitic worms

Summary

Introduction

Helminth infections affect more than 1.5 billion people globally and are common amongst economically deprived populations [1, 2]. Though rarely fatal, cause considerable morbidity [8, 9]. Heavy intensity helminth infections can impair physical growth and cognitive development, and lead to micronutrient deficiencies and anemia [3, 10]. Chronic helminth infection is detrimental to the functioning of the immune response against infectious diseases such as TB and, increases the risk of developing TB in later life [14]. Associations between TB and helminth infections have been reported for school-aged and adult populations [6, 15]. Despite the high prevalence of helminth infections among preschool-aged children, control programs in sub-Saharan countries primarily focus on school-aged populations. We assessed the prevalence of helminth infections and determined risk factors for infection among preschool-aged children in the urban setting of Dar es Salaam, Tanzania

Methods

Results

Discussion

Conclusion