Towards understanding the liver fluke transmission dynamics on farms: Detection of liver fluke transmitting snail and liver fluke-specific environmental DNA in water samples from an irrigated dairy farm in Southeast Australia

Livestock production around the world is impacted by liver fluke (Fasciola spp.) infection resulting in serious economic losses to the beef, dairy and sheep industries with significant losses of about $90 million per annum in Australia. Triclabendazole (TCBZ) is the most effective anthelmintic treatment available to control liver fluke infections; however, the widespread emergence of TCBZ resistance in livestock threatens liver fluke control. Alternative control measures to lower exposure of livestock to liver fluke infection would help to preserve the usefulness of current anthelmintic treatments. Environmental DNA (eDNA) based identification of liver fluke and the intermediate snail host in the water bodies is a robust method to assess the risk of liver fluke infection on farms. In this study, we used a multiplex quantitative PCR assay of water samples to detect and quantify eDNA of Fasciola hepatica (F. hepatica) and Austropeplea tomentosa (A. tomentosa), a crucial intermediate snail host for liver fluke transmission in South-east Australia. Water samples were collected from an irrigation channel for a period of 7 months in 2016 (February, March, May, September, October, November and December) at a dairy farm located at Maffra, Victoria, South-east Australia. Using an effective eDNA extraction method, the multiplex qPCR assay allows for the independent but simultaneous detection of eDNA released from liver fluke life stages and snails using specific primers and a probe targeting the ITS-2 region of the liver fluke and snail, respectively, with minimal inhibition from contaminants in field collected water samples. The sensitivity of this assay to detect eDNA of liver fluke and snails was observed to be 14 fg and 50 fg, respectively, in the presence of field collected water samples. Differential levels of liver fluke and snail specific eDNA in water were observed at the time points analysed in this study. The successful detection of eDNA specific to liver fluke and snails from the field collected water samples provides a precedent for the use of this method as a monitoring tool to determine the prevalence of liver fluke and liver fluke-transmitting snails in irrigation regions. Further, this method has the enormous potential to allow an assessment of the liver fluke transmission zones on farms and to inform the application of effective control strategies.

Development of a multiplex quantitative PCR assay for detection and quantification of DNA from Fasciola hepatica and the intermediate snail host, Austropeplea tomentosa, in water samples

Liver fluke (Fasciola hepatica) infection is an increasing threat to livestock production resulting in serious economic losses to the beef, dairy and sheep industries in Australia and globally. Triclabendazole (TCBZ) is the main drug used to control liver fluke infections in Australia and the widespread emergence of TCBZ resistance in cattle and sheep threatens liver fluke control. Alternative control measures to lower exposure of livestock to fluke infection would be useful to help preserve the usefulness of current chemical flukicides. Environmental DNA (eDNA) sampling methodology and associated molecular techniques are suited to rapidly assess the presence of pathogens on farms. In the present study, we developed a water sampling method in combination with a multiplex quantitative PCR assay to detect and quantify DNA of F. hepatica and Austropeplea tomentosa (A. tomentosa), a crucial intermediate snail host for liver fluke transmission in South-east Australia. The multiplex qPCR assay allows for the independent detection of F. hepatica and A. tomentosa DNA using specific primers and a probe targeting the ITS-2 region of the liver fluke or snail. The method allows the highly specific and sensitive (minimal DNA detection levels to 14-50 fg) detection of F. hepatica or A. tomentosa. The method allows the detection of both liver fluke and snail eDNA in water samples. The effective quantification of liver fluke and snail eDNA in water samples using this assay could potentially allow researchers to both identify and monitor F. hepatica transmission zones on farming properties in South-east Australia which will better inform control strategies, with potential application of the assay worldwide.