2018 is proving to be a difficult year for fluke forecasting!
The graph below shows that, for the Scotland West Met Office region, the number of days with 1mm or more of rain this summer is similar to 2015 which was an average risk year for liver fluke.
However the pattern of rainfall was different this year with June and July being dry – more like 2013 and 2014 which were low risk liver fluke years. Early summer will have been unfavourable for both Galba truncatula and the environmental stages of Fasciola hepatica, except in the very wettest areas of fields.
Scotland West number of wet days (≥1mm rain) June to September
Some things to consider are as follows:
- We have post mortemed numerous ill thriven lambs recently and none have had any evidence of liver fluke infection – just massive worm burdens
- During September we detected liver fluke eggs in a small number of lamb faecal samples as we do every year. This probably reflects infection picked up much earlier in the year
- We are still finding plenty of liver fluke eggs in samples submitted from older age groups indicating that pasture contamination has continued throughout the summer
- Submissions of lamb blood samples (from SW Scotland and NW England) for F. hepatica antibody testing have often been completely negative or returned only one or two positives suggesting low fluke challenge on these farms up until now
Overall the fluke risk seems likely to be low to average for Dumfries and Galloway. Based on previous years following drier summers there are fewer acute fluke deaths with diagnoses peaking in December, rather than late October.
Potential ways forward are as follows:
- Collect samples to check whether or not animals close to finishing need to be treated this autumn. The area they are grazing should also be taken into account
- The blood Fascioloa hepatica ELISA or faecal coproantigen ELISA tests are very useful in this regard. Antibodies can be detected in serum from 2 weeks after infection with liver fluke and coproantigen can be detected 6-8 weeks after infection
- Consider treating with closantel or nitroxynil instead of triclabendazole in lower risk situations, to help reduce the risk of inducing triclabendazole resistance
- Investigate deaths later in the year promptly, particularly on farms that used flukicides as early as September
- Always consider that farm and indeed field specific conditions can be very variable so advice for individual farms needs to be considered
For more detailed information on liver fluke Heather Stevenson has written a technical note providing up to date information for both vets and farmers. This note can be downloaded here.