The main message for livestock farmers in relation to liver fluke this year is to “test, don’t guess’.
Sustainable Control of Parasites in Sheep (SCOPS) and Control of Cattle Parasites Sustainable (COWS) have labelled 2023 as a “very strange year” in terms of weather patterns and parasites.
On behalf of COWS, Prof Diana Williams of the University of Liverpool said:
“2023 has been a funny old year. A very dry cold spring was followed by a hot early summer and then July and August were extremely wet.
“Top that off with the mini heatwave in early September accompanied by heavy rain, and it is fair to say there will be an impact on levels and timing of the risks faced by grazing livestock this season.”
The National Animal Disease Information Service’s (NADIS) fluke forecast, which is based on local weather patterns, is generally predicting a low-to-medium risk, with the exception of high-risk hotspots in Scotland.
SCOPS and COWS said this is almost certainly due to how dry it was at the start of the year and, while recent months may have been ideal for the fluke and snail lifecycles, the total window for their development has been relatively short.
“Liver fluke and its intermediate host, the mud snail galba truncatula, require temperatures of more than 10o to remain active and continue development, so if we have a warm autumn and early winter the risk may still increase later in the year, particularly if the conditions also tempt farmers to keep their livestock out later,” Williams said,
“The serum antibody ELISA test, which is done on blood samples taken from 10 individuals is an extremely valuable tool in these circumstances.
“Using this test, we can monitor lambs or calves born in 2023 to look for evidence of exposure to liver fluke.
“Repeated at regular intervals, this not only means we can check for exposure but also when that exposure occurs, which reduces the risk of unnecessary or mistimed treatments.”
SCOPS independent sheep consultant, Lesley Stubbings, said: “Anecdotally, we’ve not seen much liver fluke across the country this year so far.”
In contrast, Stubbings highlighted the increase in cases of haemonchosis in sheep, which is caused by the highly pathogenic roundworm haemonchus contortus (also known as the barber’s pole worm).
“The conditions in the UK this summer and last summer have seemingly suited this worm, which is common in many tropical and sub-tropical regions of the world,” Stubbings said.
“Because clinical signs of anaemia, bottle jaw and weight loss can result from the blood-feeding behaviour of either liver fluke or haemonchus, this can be confusing.
“Differential diagnosis is all the more important and underlines the need to ‘Test, don’t guess’.”
Experts from both SCOPS and COWS have urged caution to any producers looking to use the ELISA test but thinking of trying to cut the cost by pooling blood samples rather than testing individuals.
“The sensitivity of a pooled test is much lower and may give a negative result even though one or more animals are positive,” Stubbings said.
“This means that tests need to be done more regularly (every 10-14 days) to try to ensure the exposure is not missed, which will probably cancel out any cost saving compared to individual blood testing every three to four weeks.”