Discussion
Sheep are very good hosts for F. hepatica and tend to shed a large number of eggs. This is not only an effect of the dilution factor but also because adult liver fluke produce about 200 times more eggs in sheep than in other species (i.e. up to 20,000 eggs per day). This makes the sheep a very good host for liver fluke. The sensitivity of the detection method for this species is therefore not very critical and was not included in this validation. The number of eggs in faeces of cattle and horses on the other hand can be very low. In horses with F. hepatica infection as few as three eggs in 10g have been reported.
The validation showed that at least one egg/g (1/2 egg/g for horses) can be detected with our technique provided that a faecal sample of 10g faeces is examined. However, using 4g of faeces for cattle (current protocol) the detection limit was only at 10 eggs/g. This indicates that the total number of eggs present in the sample is more critical for the sensitivity of the technique than the egg concentration. Egg recovery in larger samples is probably lowered but the detection limit is still better. The detection limit for the glass bead sieving technique described by Taira (1985) was four eggs/g using a sample of 1g of faeces only. It is possible that this detection limit could be improved if the glass bead technique could be adapted to the processing of larger sample sizes.
Recommendation
We recommend that the currently used sedimentation method for the detection trematode eggs be modified to change the sample size for cattle from 4g to 10g.
All three sieves (150 micron, 90 micron and 45 micron) should be used for sample preparation (no change of method). However, extreme care has to be taken to avoid overflow of sample material.
We also recommend that all laboratories conducting testing for the presence of liver fluke in WA be tested for their ability to detect liver fluke eggs in samples spiked with eggs at the detection limit of the assay every 6 months (QA control).
References
4246 Boray JC, Pearson IG. The anthelminic efficiency of tetrachlorodifluoroethane in sheep infested with Fasciola hepatica. Aust Vet J 1960; 36: 331–337.
2209 Breza M, Corba J. Comparison of coprological methods in fasciolosis of cattle. Helminthologia 1973; 14: 135–141.
1986 Happich FA, Boray JC. Quantitative diagnosis of chronic fasciolosis. Aust Vet J 1969; 45: 326–328.
4445 Taira N. Sieving technique with the glass beads layer for detection and quantification of Fasciola eggs in cattle faeces. JARQ 1985; 18: 290–297.
Important disclaimer
The Chief Executive Officer of the Department of Primary Industries and Regional Development and the State of Western Australia accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.
Copyright Western Australian Agriculture Authority, 2013 (now State of Western Australia (Department of Primary Industries and Regional Development)
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Issue No. 16