Abstract
Soil-transmitted helminth (STH) infections are widespread in tropical and subtropical regions. While many STH infections are asymptomatic, vulnerable populations such as pregnant women face repercussions such as aggravation of maternal anaemia. However, data on prevalence and the effect of STH infections in pregnancy are limited. The aim of this analysis was to describe the burden of STH infections within and between populations of pregnant women from a local refugee camp to a mobile migrant population, and to explore possible associations between STH infection and pregnancy outcomes. This is a retrospective review of records from pregnant refugee and migrant women who attended Shoklo Malaria Research Unit antenatal care (ANC) clinics along the Thailand-Myanmar border between July 2013 and December 2017. Inclusion was based on provision of a stool sample during routine antenatal screening. A semi-quantitative formalin concentration method was employed for examination of faecal samples. The associations between STH mono-infections and maternal anaemia and pregnancy outcomes (i.e., miscarriage, stillbirth, preterm birth, and small for gestational age) were estimated using regression analysis. Overall, 12,742 pregnant women were included, of whom 2,702 (21.2%) had a confirmed infection with either Ascaris lumbricoides, hookworm, Trichuris trichiura, or a combination of these. The occurrence of STH infections in the refugee population (30.8%; 1,246/4,041) was higher than in the migrant population (16.7%; 1,456/8,701). A. lumbricoides was the predominant STH species in refugees and hookworm in migrants. A. lumbricoides and hookworm infection were associated with maternal anaemia at the first ANC consultation with adjusted odds ratios of 1.37 (95% confidence interval (CI) 1.08-1.72) and 1.65 (95% CI 1.19-2.24), respectively. Pregnant women with A. lumbricoides infection were less likely to miscarry when compared to women with negative stool samples (adjusted hazard ratio 0.63, 95% CI 0.48-0.84). STH infections were not significantly associated with stillbirth, preterm birth or being born too small for gestational age. One in five pregnant women in this cohort had STH infection. Association of STH infection with maternal anaemia, in particular in the event of late ANC enrolment, underlines the importance of early detection and treatment of STH infection. A potential protective effect of A. lumbricoides infection on miscarriage needs confirmation in prospective studies.
Highlights
Estimates from the World Health Organization (WHO) suggest that approximately 25% of the world’s population is infected with soil-transmitted helminths (STHs) [1], causing a global burden of 1.92 million disability-adjusted life years (DALYs) [2]
Between July 2013 and December 2017, 83.9% (12,742/15,191) of all women registered to antenatal care (ANC) at Shoklo Malaria Research Unit (SMRU) were included in this analysis (Fig 2)
As these procedures became routine in the second half of 2013, and as ANC operations ceased in Mae La refugee camp at the end of 2016, the total number of tests was lower in 2013 and 2017, compared to the other years (S2 Table)
Summary
Estimates from the World Health Organization (WHO) suggest that approximately 25% of the world’s population is infected with soil-transmitted helminths (STHs) [1], causing a global burden of 1.92 million disability-adjusted life years (DALYs) [2]. Intestinal helminthiasis has repercussions on nutritional uptake leading to reduced food intake, impaired digestion, and malabsorption [5]. The latter predominantly leads to unfavourable consequences, such as poor growth or development in children and depletion of iron stores with subsequent anaemia [5]. Maternal anaemia is a public health issue in many regions, often aggravated by STH infection and associated with unfavourable pregnancy outcomes [3,6,7]. Chronic blood loss and mucosal inflammation caused by intestinal nematode infections increase with intensity of infection and explain the association between hookworm infection and anaemia in pregnancy and, to a smaller extent, T. trichiura infection [8,9,10].
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