Potential vertical transmission of genetically diverse Trypanosoma cruzi in natural rodent populations

Trypanosoma cruzi, the causative agent of Chagas disease, has been detected in mammalian hosts occupying densely populated urban environments. This suggests that the risk of transmission to humans is higher than prevailing estimates, which largely reflect conditions in rural and peri-urban areas. Understanding the risks posed by T. cruzi thus requires further study of transmission pathways in part because triatomines - the primary vectors for T. cruzi - appear to be uncommon or absent in urban landscapes. Here we test the hypothesis that vertical transmission contributes to the prevalence of infection and diversity of T. cruzi in urban reservoirs.

We assessed whether embryos of T. cruzi-positive parous female rodents also exhibit evidence of infection. A diagnostic PCR assay detected T. cruzi in 15 out of 66 (22.7%) embryos from Norway rats, black rats, and house mice captured in New Orleans (LA, USA). Genotyping PCR identified the presence of TcI and non-TcI discrete typing units (DTUs) in individual infected embryos, providing evidence of mixed infection. Next-generation sequencing provided additional evidence of mixed infection in individual embryos.

Our findings provide additional evidence that vertical transmission can occur in natural populations of reservoir species and demonstrates for the first time that multiple DTUs can transmit from mother to offspring. Our study also demonstrates that vertical transmission can contribute to the prevalence of infection and diversity of T. cruzi in multiple reservoir species occupying urban landscapes where vectors appear to be rare or absent, providing a new baseline for understanding transmission pathways and eco-epidemiological cycling of T.cruzi.