Burden of soil-transmitted helminth infection in pregnant refugees and migrants on the Thailand-Myanmar border: Results from a retrospective cohort

Author summary Soil-transmitted helminths (STHs) are parasitic worms transmitted through the faecal-oral route. STHs are ubiquitous in tropical and subtropical regions where access to clean water, improved sanitation, and hygiene are lacking. STH infections are often asymptomatic; however, heavy infections can cause adverse effects such as abdominal discomfort and anaemia. Anaemia in pregnancy can increase the risk of pregnancy problems such as miscarriage, preterm delivery, and poor fetal growth. This retrospective analysis of routinely collected data from more than 12,000 pregnant refugee and migrant women who attended antenatal care clinics along the Thai-Myanmar border shows that one in five pregnant women were infected with STHs. Moreover, pregnant women with a STH infection were more likely to present with anaemia, suggesting that early presentation to antenatal care as well as anthelmintic treatment with subsequent anaemia prophylaxis may reduce the risk of anaemia. Interestingly, our data also indicate that STH infections may have beneficial effects on pregnancy outcomes, as miscarriage was less likely to occur in pregnancies with maternal STH infections. This finding was significant for infection with the roundworm Ascaris lumbricoides. Verification of these findings in prospective studies is warranted. Background Soil-transmitted helminth (STH) infections are widespread in tropical and subtropical regions. While many STH infections are asymptomatic, vulnerable populations (e.g., 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. Methodology 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. Principal findings 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 and 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.