Authors

A Singh¹; S Chaurasiya²; T Banerjee²; A Tiwari²;  ¹ University of Edinburgh, UK;  ² Banaras Hindu University, India

Discussion

Background

Fasciolopsiasis, caused by the giant intestinal fluke, Fasciolopsis buski (F. buski), is a significant cause of morbidity and mortality in South and South-east Asia. This parasite has been widely reported, often in case reports based on morphometric identification or incidental identification of endemic foci. However, genetic analysis of this parasite is limited. Importantly, F. buski is found in multiple hosts species, including pigs, and the genetic diversity of this parasite isolated from these hosts is largely unknown.

Methodology

Following endoscopy, worms were isolated from the duodenum of a 50-year-old male in Uttar Pradesh, India. Morphological analysis presumptively identified these worms to be a giant intestinal fluke; leaf-like structure, 3-4cm in length, anterior end broad without conical projection, and ventral sucker close to the oral sucker. DNA was then extracted for 28s rDNA and ITS2 amplification and sequencing. Consensus sequences were generated using Bioedit software and species identification performed using blastn. Multiple sequence alignment with query-anchored dots for analysis was done for F. buski species to understand intra species and interspecies homology. Phylogenetic analysis was done using clustalW program of MEGA software and the evolutionary history was inferred using the Neighbor-Joining method.

Results

The parasite showed close similarity to an isolate from pig in one of the north-eastern states in India, Meghalaya, thus affirming the zoonotic cross-transmission of this parasite. The intra species genetic variation for 28S rDNA of F. buski was 1-3% from the isolates of India, 5% from Vietnam and 8-11% with other related trematodes. For ITS2 the intra-species genetic variation was 1-2% from isolates of India while 17% from Vietnam and 3-28% among other trematodes. On phylogenetic analysis, F. buski isolated from humans or pigs from India were closely related, as compared to those from Vietnam and China, which were grouped into separate clades.

Conclusions

Using a fluke isolated from a human patient, we found that this parasite matched the sequence of F. buski found in Indian pigs and that these fluke in India were genetically distinct from those found in Vietnam, at least by 28S rDNA and ITS2 region. Therefore, F. buski from India may represent a distinct clade different than those Vietnam and China, which are more closely related. Future studies are needed to elucidate the mechanisms and consequences of zoonotic transmission of F. buski in India.