# The underestimated burden of placental schistosomiasis in endemic regions: Findings from a cross-sectional, diagnostic proof-of-concept study on placental schistosomiasis in Gabon

## TL;DR

This study finds that placental schistosomiasis is more common than previously thought, even in women without detectable infection in urine, suggesting it may be an underestimated health risk in endemic regions.

## Contribution

The study introduces an improved placenta maceration technique to detect placental schistosomiasis in real-world conditions, revealing its underdiagnosed prevalence.

## Key findings

- 14% of women with S. haematobium infection had placental schistosomiasis.
- 5% of women without detectable S. haematobium in urine also had placental schistosomiasis.
- qPCR confirmed all microscopy-positive placental samples for S. haematobium eggs.

## Abstract

Placental schistosomiasis (PS) is underdiagnosed and may compromise maternal and neonatal health. This study estimated the prevalence of PS in a rural Gabonese population of pregnant women with confirmed S. haematobium infection using light microscopy of macerated placental tissue.

This is a cross-sectional, diagnostic proof-of-concept study which applied an improved placenta maceration technique in real-world conditions to diagnose PS. Performing light microscopic assessment of a single sample of 10 mL urine, we screened pregnant women for S. haematobium infection who sought antenatal care in Lambaréné (Gabon) between January 2022 and January 2023. Women positive for S. haematobium infection were followed up until delivery. Additionally, a subsample of women with negative urine samples was recruited as a non-infected control group (1:1 ratio infected and non-infected groups) and followed up until delivery. Only participants with available macerated placental samples were considered for final analysis. Placental samples were subjected to light-microscopy-based screening for S. haematobium eggs and PS was considered present if a least one S. haematobium egg was detected. Positive light microscopic placental samples were confirmed by qPCR.

Among 318 women screened for S. haematobium in urine, we found 40 (12.6%; 95% CI: 9.1-16.7%) to be positive. Together with 40 women in the non-infected control group all women were followed up until delivery. After loss-to-follow-up, 28 (70%; 28/40) women with S. haematobium infection and 20 (50%; 20/40) without infection provided placenta samples at delivery. In the group with S. haematobium infection, 14% (4/28; 95% CI: 4.0-32.7%) of women were positive for S. haematobium eggs in macerated placenta tissue. In the non-infected control group, one woman (5%; 1/20; 95% CI: 0.1-24.9%) had a positive microscopy result for PS. All five women with positive S. haematobium egg microscopy in placental tissue received a concordant qPCR result.

14% of women with S. haematobium infection also had PS. Notably, PS was also observed in 5% of women without detectable S. haematobium eggs in urine. This suggests that PS could be an underestimated phenomenon in highly endemic regions and warrants further investigations of its implications for mother-and-child health.

Schistosomiasis is a neglected disease that affects millions of people, mostly in sub-Saharan Africa. One of the main species, Schistosoma haematobium, is known to infect the urinary and genital organs; however, little is known about this infection during pregnancy, and even less is known about whether the parasite can affect the placenta. We collected placental tissue from women with and without S. haematobium infection and applied a laboratory method that allowed for the examination of large amounts of tissue. A total of 318 pregnant women participated in this study among whom 40 women tested positive for S. haematobium eggs in urine. Those with S. haematobium infection and a control group of 40 women without detectable eggs in urine were followed-up until birth. Among the 28 infected participants who could be followed-up until birth eggs were found in the placenta of four women, but also in one woman without detectable infection in urine. These results show that the parasitic infection can involve the pregnant uterus and the placenta. This underlines the need to better understand S. haematobium infection during pregnancy and supports ongoing efforts to better understand its implications for mother-and-child health.