Placentas from healthy women living in a cutaneous leishmaniasis endemic region in Mexico harbor Leishmania mexicana parasites: Potential implications for pregnancy and neonatal outcomes

Background. Women living in leishmaniasis-endemic zones are regularly exposed to the sandfly vector in their environments. While case series and laboratory evidence consistently suggest transplacental transmission of Leishmania parasites with deleterious maternal-fetal effects, this issue has received insufficient attention, particularly in areas where the predominant Leishmania species is mainly associated with cutaneous disease (CL). Methodology/Principal Findings. We conducted an exploratory cross-sectional study in a highly endemic zone of Tabasco, Mexico, enrolling 53 women with singleton term deliveries between April 2018 and April 2020. Placental PCR was positive in 18 (34%) participants. Buccal swabs were positive in 11 (21.2%) of 52 newborns. Immunofluorescence confirmed intracellular amastigotes within macrophages near the vascular endothelium of PCR-positive placentas, with no surrounding inflammatory infiltration. Sequencing revealed homology to Leishmania mexicana or L. amazonensis. Birthweight percentile was modestly lower in the PCR-positive group (predicted mean 53.8% vs. 56.5%, p = 0.76), while small for gestational age showed a non-significant trend toward higher prevalence among PCR-positive cases (prevalence ratio = 2.06, 95% CI: 0.32-13.39, p = 0.45). Conclusions/Significance. Subclinical, dynamic transmission of Leishmania parasites typically associated with cutaneous disease was detected in this endemic zone. The presence of L. mexicana in human placentas was confirmed by immunofluorescence and sequencing, without an associated inflammatory response. These findings highlight the potential of CL-associated Leishmania species to reach the placenta and buccal mucosa of newborns, warranting further epidemiological investigation into the consequences of vertical transmission in regions with endemic CL.