New research suggests microbial partners may affect parasites

A new study from the Mitreva lab sheds light on the relationship between the liver fluke Fasciola hepatica and its bacterial endosymbiont, Neorickettsia. Researchers found that while these bacteria are widely present in fluke populations across the Americas and Europe, they show low genetic diversity and strong geographic patterning. Their results suggest a complex evolutionary history shaped by both long-term inheritance from parent to offspring and occasional transmission between hosts. Their findings were published in the journal Current Research in Parasitology & Vector-Borne Diseases.

Population genomics of Neorickettsia endobacteria Fasciola hepatica (nFh) Of 502 F. hepatica WGS sample screened, there were 88 Neorickettsia-positive samples and 77 nFh consesus genomes. This suggests low genetic diversity and structured populations, cophylogeny congruent with the host nuclear genome, and mixed vertical and horizontal transmission. The study identified a strong association between Neorickettsia infection and triclabendazole resistance in one region of Peru, namely Cusco, while Cajamarca shows no association. Map shows Neorickettsia endobacteria associated with the liver fluke Fasciola hepatica are widely distributed across the U.S., Peru, Uruguay and U.K. — A recent study from the Mitreva lab shows that Neorickettsia endobacteria associated with the liver fluke Fasciola hepatica are widely distributed across the Americas and Europe but exhibit low genetic diversity and pronounced geographic population structure. The study identified a strong association between Neorickettsia infection and triclabendazole resistance in one region of Peru. This finding suggests that the endosymbiont may contribute to drug-resistance patterns in a geographically or epidemiologically specific manner.

The study also points to a potential connection between Neorickettsia infection and resistance to triclabendazole, a key drug used to treat liver fluke infections. In one region of Peru, the researchers observed a strong association between bacterial infection and drug resistance, raising the possibility that the endosymbiont may influence how resistance emerges or spreads in certain settings. While the biological role of Neorickettsia is still not fully understood, these findings open new questions about how microbial partners may affect parasite biology and treatment outcomes.

Pawan Kumar, Young-Jun Choi, Martha V. Fernandez-Baca, Maria Luisa Morales, Pedro Ortiz, Cristian Hoban, Miguel M. Cabada, Makedonka Mitreva. Genetic diversity and host-symbiont cophylogenetic analysis of Neorickettsia endobacteria of Fasciola hepatica. Current Research in Parasitology & Vector-Borne Diseases. Volume 10, 2026, 100409. ISSN 2667-114X. https://doi.org/10.1016/j.crpvbd.2026.100409.

ETHICAL APPROVAL: This study involved secondary analysis of publicly available whole-genome sequencing data from the NCBI Sequence Read Archive (SRA). No new human or animal samples were collected, and no identifiable private information was used. Therefore, no ethical approval was required for this study.

FUNDING: This research was funded by the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, USA (grant number 1R01AI146353). Declaration of competing interests