Monitoring For Liver Fluke Infection This Autumn
The challenge of liver fluke over the last couple of winters has been lower than average in South West Scotland. The dry and sunny weather during spring and early summer 2020 will not have been favourable for the environmental stages of Fasciola hepatica, nor for multiplication of the intermediate host snail Galba truncatula. This slow start means that cercarial shedding from snails may be later than usual. This autumn will therefore be a good year to monitor first season grazing animals for evidence of liver fluke infection as disease risk may be less or later this year and treatment may not be required in all cases.
Knowledge of the farm’s liver fluke history and whether the land being grazed is high or low risk is also useful. It may be that lambs can be sold fat in September and October without treatment; saving time, money and avoiding the need to observe withdrawal periods.
Seroconversion occurs within 2 to 4 weeks of infection with F. hepatica metacercariae and serology gives one of the earliest indications of liver fluke infection. A red top tube is required for the antibody ELISA and the test can be carried out on blood samples collected for trace element monitoring around weaning time. Samples could also be collected if lambs are being gathered regularly for weighing or when investigating problems with ill thrift. Six samples per group is adequate.
Suckled calves and dairy calves in their first grazing season can also be used as sentinels with samples ideally collected a couple of weeks after housing. Depending on grazing strategies older dairy heifers may also be suitable candidates for serology. Bulk tank monitoring can be useful in low risk, closed dairy herds with monthly samples collected either side of housing to look for a rising titre.
If you wish to discuss sampling strategies further, please get in touch.
Posted by Veterinary Services on 03/08/2020