Authors

P Best³; L Phuong⁵; J Campbell⁵; T Hien⁵; R Hanna⁴; J LaCourse¹; K Cwiklinski⁶; JP Dalton²; MW Robinson³;  ¹ Liverpool School of Tropical Medicine, UK;  ² National University of Ireland, Galway (NUI Galway), Ireland;  ³ Queens University Belfast, UK;  ⁴ Agri-Food Biosciences Institute, Belfast, UK;  ⁵ Oxford University Clinical Research Unit, Centre for Tropical Medicine, Ho Chi Minh City, Vietnam;  ⁶ Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, UK

Discussion

Although traditionally regarded as a disease of livestock, fasciolosis is now recognised as an emerging zoonotic disease with at least 2.4 million people infected worldwide. The major causative agents of fasciolosis are Fasciola hepatica and F. gigantica, in regions with temperate and tropical climates respectively, although hybrid forms have also emerged, notably in Southeast Asia. Whilst animal fasciolosis is endemic throughout this region, central Vietnam has emerged as a particular “hotspot” for human infection. In a bid to identify the predominant Fasciola species in this area, liver flukes were collected from cattle at abattoirs in the Phu Yen and Binh Dinh provinces and subjected to molecular speciation via multiplex-PCR and restriction fragment length polymorphism of phosphoenolpyruvate carboxykinase (pepck) and DNA polymerase delta (pold) genes respectively. Out of 326 adult flukes, 36 (11%) were identified as F. gigantica whilst 290 (89%) were identified as hybrid/intermediate forms. No flukes were identified as F. hepatica using these genetic markers. The reproductive strategy of the flukes was also assessed by aceto-orcein squash and histological observation. The majority of hybrid flukes were found to be aspermic, and thus likely to reproduce via parthenogenesis. However, a small number of hybrids did contain limited numbers of sperm but they displayed abnormal morphology and are unlikely to be viable. Our data show that hybrid Fasciola are the dominant form in the Phu Yen and Binh Dinh provinces. Given the absence of F. hepatica in this region, it is likely that hybrids were introduced to central Vietnam via import of infected livestock. However, further molecular analysis is required to confirm this.